update x/tools

Significantly improve CPU and memory usage when not using SSA-powered linters.
Improve readability of go/packages errors.
Improve debugging capabilities and write doc about debugging.

.travis.yml

@@ -5,7 +5,8 @@ go:
   - 1.12.x
 
 before_script:
-  - go get github.com/valyala/quicktemplate
+  - go get github.com/valyala/quicktemplate # for tests
+  - go get github.com/pkg/errors # for tests
 
 script: make check_generated test
 

Makefile

@@ -30,7 +30,8 @@ test_linters:
 
 # Maintenance
 
-generate: docs/demo.svg README.md install.sh pkg/logutils/log_mock.go vendor
+generate: README.md install.sh pkg/logutils/log_mock.go vendor
+generate_svg: docs/demo.svg
 maintainer-clean: clean
 	rm -f docs/demo.svg README.md install.sh pkg/logutils/log_mock.go
 	rm -rf vendor

README.md

@@ -28,6 +28,7 @@ Sponsored by [GolangCI.com](https://golangci.com): SaaS service for running lint
 * [FAQ](#faq)
 * [Thanks](#thanks)
 * [Changelog](#changelog)
+* [Debug](#debug)
 * [Future Plans](#future-plans)
 * [Contact Information](#contact-information)
 
@@ -1140,6 +1141,20 @@ There is the most valuable changes log:
 1. Support GitHub Releases
 2. Installation via Homebrew and Docker
 
+## Debug
+
+You can see a verbose output of linter by using `-v` option.
+
+If you would like to see more detailed logs you can set environment variable `GL_DEBUG` to debug `golangci-lint`.
+It's value is a list of debug tags. For example, `GL_DEBUG=loader,gocritic golangci-lint run`.
+Existing debug tags:
+
+1. `gocritic` - debug `go-critic` linter;
+2. `env` - debug `go env` command;
+3. `loader` - debug packages loading (including `go/packages` internal debugging);
+4. `autogen_exclude` - debug a filter excluding autogenerated source code;
+5. `nolint` - debug a filter excluding issues by `//nolint` comments.
+
 ## Future Plans
 
 1. Upstream all changes of forked linters.

README.tmpl.md

@@ -28,6 +28,7 @@ Sponsored by [GolangCI.com](https://golangci.com): SaaS service for running lint
 * [FAQ](#faq)
 * [Thanks](#thanks)
 * [Changelog](#changelog)
+* [Debug](#debug)
 * [Future Plans](#future-plans)
 * [Contact Information](#contact-information)
 
@@ -668,6 +669,20 @@ There is the most valuable changes log:
 1. Support GitHub Releases
 2. Installation via Homebrew and Docker
 
+## Debug
+
+You can see a verbose output of linter by using `-v` option.
+
+If you would like to see more detailed logs you can set environment variable `GL_DEBUG` to debug `golangci-lint`.
+It's value is a list of debug tags. For example, `GL_DEBUG=loader,gocritic golangci-lint run`.
+Existing debug tags:
+
+1. `gocritic` - debug `go-critic` linter;
+2. `env` - debug `go env` command;
+3. `loader` - debug packages loading (including `go/packages` internal debugging);
+4. `autogen_exclude` - debug a filter excluding autogenerated source code;
+5. `nolint` - debug a filter excluding issues by `//nolint` comments.
+
 ## Future Plans
 
 1. Upstream all changes of forked linters.

go.mod

@@ -52,7 +52,6 @@ require (
 	github.com/timakin/bodyclose v0.0.0-00010101000000-000000000000
 	github.com/valyala/quicktemplate v1.1.1
 	golang.org/x/crypto v0.0.0-20190313024323-a1f597ede03a // indirect
-	golang.org/x/net v0.0.0-20190313220215-9f648a60d977 // indirect
 	golang.org/x/sys v0.0.0-20190312061237-fead79001313 // indirect
 	golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd
 	gopkg.in/airbrake/gobrake.v2 v2.0.9 // indirect
@@ -63,5 +62,8 @@ require (
 	mvdan.cc/unparam v0.0.0-20190124213536-fbb59629db34
 )
 
-// https://github.com/timakin/bodyclose/pull/17
+replace (
-replace github.com/timakin/bodyclose => github.com/golangci/bodyclose v0.0.0-20190713050349-65da19158fa2
+	// https://github.com/timakin/bodyclose/pull/17
+	github.com/timakin/bodyclose => github.com/golangci/bodyclose v0.0.0-20190713050349-65da19158fa2
+	golang.org/x/tools => github.com/golangci/tools v0.0.0-20190713050349-979bdb7f8cc8
+)

go.sum

@@ -81,6 +81,8 @@ github.com/golangci/prealloc v0.0.0-20180630174525-215b22d4de21 h1:leSNB7iYzLYSS
 github.com/golangci/prealloc v0.0.0-20180630174525-215b22d4de21/go.mod h1:tf5+bzsHdTM0bsB7+8mt0GUMvjCgwLpTapNZHU8AajI=
 github.com/golangci/revgrep v0.0.0-20180526074752-d9c87f5ffaf0 h1:HVfrLniijszjS1aiNg8JbBMO2+E1WIQ+j/gL4SQqGPg=
 github.com/golangci/revgrep v0.0.0-20180526074752-d9c87f5ffaf0/go.mod h1:qOQCunEYvmd/TLamH+7LlVccLvUH5kZNhbCgTHoBbp4=
+github.com/golangci/tools v0.0.0-20190713050349-979bdb7f8cc8 h1:rv5pCF5e6hFuSWEDuP3R+r8l0n/srMta+VWVEskASSQ=
+github.com/golangci/tools v0.0.0-20190713050349-979bdb7f8cc8/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 github.com/golangci/unconvert v0.0.0-20180507085042-28b1c447d1f4 h1:zwtduBRr5SSWhqsYNgcuWO2kFlpdOZbP0+yRjmvPGys=
 github.com/golangci/unconvert v0.0.0-20180507085042-28b1c447d1f4/go.mod h1:Izgrg8RkN3rCIMLGE9CyYmU9pY2Jer6DgANEnZ/L/cQ=
 github.com/google/go-cmp v0.2.0 h1:+dTQ8DZQJz0Mb/HjFlkptS1FeQ4cWSnN941F8aEG4SQ=
@@ -177,9 +179,8 @@ golang.org/x/net v0.0.0-20170915142106-8351a756f30f/go.mod h1:mL1N/T3taQHkDXs73r
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd h1:nTDtHvHSdCn1m6ITfMRqtOd/9+7a3s8RBNOZ3eYZzJA=
 golang.org/x/net v0.0.0-20180906233101-161cd47e91fd/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20180911220305-26e67e76b6c3/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
-golang.org/x/net v0.0.0-20190311183353-d8887717615a/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859 h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=
-golang.org/x/net v0.0.0-20190313220215-9f648a60d977 h1:actzWV6iWn3GLqN8dZjzsB+CLt+gaV2+wsxroxiQI8I=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
-golang.org/x/net v0.0.0-20190313220215-9f648a60d977/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f h1:wMNYb4v58l5UBM7MYRLPG6ZhfOqbKu7X5eyFl8ZhKvA=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
@@ -193,16 +194,7 @@ golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/text v0.0.0-20170915090833-1cbadb444a80/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
-golang.org/x/tools v0.0.0-20170915040203-e531a2a1c15f/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-golang.org/x/tools v0.0.0-20180221164845-07fd8470d635/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20181117154741-2ddaf7f79a09/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20190110163146-51295c7ec13a/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20190121143147-24cd39ecf745/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
-golang.org/x/tools v0.0.0-20190311215038-5c2858a9cfe5/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
-golang.org/x/tools v0.0.0-20190322203728-c1a832b0ad89/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
-golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd h1:7E3PabyysDSEjnaANKBgums/hyvMI/HoHQ50qZEzTrg=
-golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd/go.mod h1:RgjU9mgBXZiqYHBnxXauZ1Gv1EHHAz9KjViQ78xBX0Q=
 gopkg.in/airbrake/gobrake.v2 v2.0.9 h1:7z2uVWwn7oVeeugY1DtlPAy5H+KYgB1KeKTnqjNatLo=
 gopkg.in/airbrake/gobrake.v2 v2.0.9/go.mod h1:/h5ZAUhDkGaJfjzjKLSjv6zCL6O0LLBxU4K+aSYdM/U=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

pkg/golinters/goanalysis/linter.go

@@ -124,13 +124,13 @@ func (lnt Linter) Run(ctx context.Context, lintCtx *linter.Context) ([]result.Is
 	}
 
 	var issues []result.Issue
-	for _, diag := range diags {
+	for i := range diags {
-		i := result.Issue{
+		diag := &diags[i]
+		issues = append(issues, result.Issue{
 			FromLinter: lnt.Name(),
 			Text:       fmt.Sprintf("%s: %s", diag.AnalyzerName, diag.Message),
 			Pos:        diag.Position,
-		}
+		})
-		issues = append(issues, i)
 	}
 
 	return issues, nil

pkg/lint/load.go

@@ -148,39 +148,19 @@ func (cl ContextLoader) buildSSAProgram(pkgs []*packages.Package) *ssa.Program {
 }
 
 func (cl ContextLoader) findLoadMode(linters []*linter.Config) packages.LoadMode {
-	maxLoadMode := packages.LoadFiles
+	//TODO: specify them in linters: need more fine-grained control.
+	// e.g. NeedTypesSizes is needed only for go vet
+	loadMode := packages.NeedName | packages.NeedFiles | packages.NeedCompiledGoFiles
 	for _, lc := range linters {
-		curLoadMode := packages.LoadFiles
 		if lc.NeedsTypeInfo {
-			curLoadMode = packages.LoadSyntax
+			loadMode |= packages.NeedImports | packages.NeedTypes | packages.NeedTypesSizes | packages.NeedTypesInfo | packages.NeedSyntax
 		}
 		if lc.NeedsSSARepr {
-			curLoadMode = packages.LoadAllSyntax
+			loadMode |= packages.NeedDeps
-		}
-		if curLoadMode > maxLoadMode {
-			maxLoadMode = curLoadMode
 		}
 	}
 
-	return maxLoadMode
+	return loadMode
-}
-
-func stringifyLoadMode(mode packages.LoadMode) string {
-	switch mode {
-	case packages.LoadFiles:
-		return "load files"
-	case packages.LoadImports:
-		return "load imports"
-	case packages.LoadTypes:
-		return "load types"
-	case packages.LoadSyntax:
-		return "load types and syntax"
-	}
-	// it may be an alias, and may be not
-	if mode == packages.LoadAllSyntax {
-		return "load deps types and syntax"
-	}
-	return "unknown"
 }
 
 func (cl ContextLoader) buildArgs() []string {
@@ -231,6 +211,58 @@ func (cl ContextLoader) makeBuildFlags() ([]string, error) {
 	return buildFlags, nil
 }
 
+func stringifyLoadMode(mode packages.LoadMode) string {
+	m := map[packages.LoadMode]string{
+		packages.NeedCompiledGoFiles: "compiled_files",
+		packages.NeedDeps:            "deps",
+		packages.NeedExportsFile:     "exports_file",
+		packages.NeedFiles:           "files",
+		packages.NeedImports:         "imports",
+		packages.NeedName:            "name",
+		packages.NeedSyntax:          "syntax",
+		packages.NeedTypes:           "types",
+		packages.NeedTypesInfo:       "types_info",
+		packages.NeedTypesSizes:      "types_sizes",
+	}
+
+	var flags []string
+	for flag, flagStr := range m {
+		if mode&flag != 0 {
+			flags = append(flags, flagStr)
+		}
+	}
+
+	return fmt.Sprintf("%d (%s)", mode, strings.Join(flags, "|"))
+}
+
+func (cl ContextLoader) debugPrintLoadedPackages(pkgs []*packages.Package) {
+	cl.debugf("loaded %d pkgs", len(pkgs))
+	for i, pkg := range pkgs {
+		var syntaxFiles []string
+		for _, sf := range pkg.Syntax {
+			syntaxFiles = append(syntaxFiles, pkg.Fset.Position(sf.Pos()).Filename)
+		}
+		cl.debugf("Loaded pkg #%d: ID=%s GoFiles=%s CompiledGoFiles=%s Syntax=%s",
+			i, pkg.ID, pkg.GoFiles, pkg.CompiledGoFiles, syntaxFiles)
+	}
+}
+
+func (cl ContextLoader) parseLoadedPackagesErrors(pkgs []*packages.Package) error {
+	for _, pkg := range pkgs {
+		for _, err := range pkg.Errors {
+			if strings.Contains(err.Msg, "no Go files") {
+				return errors.Wrapf(exitcodes.ErrNoGoFiles, "package %s", pkg.PkgPath)
+			}
+			if strings.Contains(err.Msg, "cannot find package") {
+				// when analyzing not existing directory
+				return errors.Wrap(exitcodes.ErrFailure, err.Msg)
+			}
+		}
+	}
+
+	return nil
+}
+
 func (cl ContextLoader) loadPackages(ctx context.Context, loadMode packages.LoadMode) ([]*packages.Package, error) {
 	defer func(startedAt time.Time) {
 		cl.log.Infof("Go packages loading at mode %s took %s", stringifyLoadMode(loadMode), time.Since(startedAt))
@@ -248,6 +280,7 @@ func (cl ContextLoader) loadPackages(ctx context.Context, loadMode packages.Load
 		Tests:      cl.cfg.Run.AnalyzeTests,
 		Context:    ctx,
 		BuildFlags: buildFlags,
+		Logf:       cl.debugf,
 		//TODO: use fset, parsefile, overlay
 	}
 
@@ -257,26 +290,10 @@ func (cl ContextLoader) loadPackages(ctx context.Context, loadMode packages.Load
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to load program with go/packages")
 	}
-	cl.debugf("loaded %d pkgs", len(pkgs))
+	cl.debugPrintLoadedPackages(pkgs)
-	for i, pkg := range pkgs {
-		var syntaxFiles []string
-		for _, sf := range pkg.Syntax {
-			syntaxFiles = append(syntaxFiles, pkg.Fset.Position(sf.Pos()).Filename)
-		}
-		cl.debugf("Loaded pkg #%d: ID=%s GoFiles=%s CompiledGoFiles=%s Syntax=%s",
-			i, pkg.ID, pkg.GoFiles, pkg.CompiledGoFiles, syntaxFiles)
-	}
 
-	for _, pkg := range pkgs {
+	if err := cl.parseLoadedPackagesErrors(pkgs); err != nil {
-		for _, err := range pkg.Errors {
+		return nil, err
-			if strings.Contains(err.Msg, "no Go files") {
-				return nil, errors.Wrapf(exitcodes.ErrNoGoFiles, "package %s", pkg.PkgPath)
-			}
-			if strings.Contains(err.Msg, "cannot find package") {
-				// when analyzing not existing directory
-				return nil, errors.Wrap(exitcodes.ErrFailure, err.Msg)
-			}
-		}
 	}
 
 	return cl.filterPackages(pkgs), nil
@@ -341,12 +358,12 @@ func (cl ContextLoader) Load(ctx context.Context, linters []*linter.Config) (*li
 	}
 
 	var prog *loader.Program
-	if loadMode >= packages.LoadSyntax {
+	if loadMode&packages.NeedTypes != 0 {
 		prog = cl.makeFakeLoaderProgram(pkgs)
 	}
 
 	var ssaProg *ssa.Program
-	if loadMode == packages.LoadAllSyntax {
+	if loadMode&packages.NeedDeps != 0 {
 		ssaProg = cl.buildSSAProgram(pkgs)
 	}
 

vendor/golang.org/x/tools/go/analysis/analysis.go

@@ -128,11 +128,13 @@ type Pass struct {
 	// See comments for ExportObjectFact.
 	ExportPackageFact func(fact Fact)
 
-	// AllPackageFacts returns a new slice containing all package facts in unspecified order.
+	// AllPackageFacts returns a new slice containing all package facts of the analysis's FactTypes
+	// in unspecified order.
 	// WARNING: This is an experimental API and may change in the future.
 	AllPackageFacts func() []PackageFact
 
-	// AllObjectFacts returns a new slice containing all object facts in unspecified order.
+	// AllObjectFacts returns a new slice containing all object facts of the analysis's FactTypes
+	// in unspecified order.
 	// WARNING: This is an experimental API and may change in the future.
 	AllObjectFacts func() []ObjectFact
 
@@ -161,6 +163,15 @@ func (pass *Pass) Reportf(pos token.Pos, format string, args ...interface{}) {
 	pass.Report(Diagnostic{Pos: pos, Message: msg})
 }
 
+// reportNodef is a helper function that reports a Diagnostic using the
+// range denoted by the AST node.
+//
+// WARNING: This is an experimental API and may change in the future.
+func (pass *Pass) reportNodef(node ast.Node, format string, args ...interface{}) {
+	msg := fmt.Sprintf(format, args...)
+	pass.Report(Diagnostic{Pos: node.Pos(), End: node.End(), Message: msg})
+}
+
 func (pass *Pass) String() string {
 	return fmt.Sprintf("%s@%s", pass.Analyzer.Name, pass.Pkg.Path())
 }
@@ -202,14 +213,3 @@ func (pass *Pass) String() string {
 type Fact interface {
 	AFact() // dummy method to avoid type errors
 }
-
-// A Diagnostic is a message associated with a source location.
-//
-// An Analyzer may return a variety of diagnostics; the optional Category,
-// which should be a constant, may be used to classify them.
-// It is primarily intended to make it easy to look up documentation.
-type Diagnostic struct {
-	Pos      token.Pos
-	Category string // optional
-	Message  string
-}

vendor/golang.org/x/tools/go/analysis/diagnostic.go

@@ -0,0 +1,48 @@
+package analysis
+
+import "go/token"
+
+// A Diagnostic is a message associated with a source location or range.
+//
+// An Analyzer may return a variety of diagnostics; the optional Category,
+// which should be a constant, may be used to classify them.
+// It is primarily intended to make it easy to look up documentation.
+//
+// If End is provided, the diagnostic is specified to apply to the range between
+// Pos and End.
+type Diagnostic struct {
+	Pos      token.Pos
+	End      token.Pos // optional
+	Category string    // optional
+	Message  string
+
+	// SuggestedFixes contains suggested fixes for a diagnostic which can be used to perform
+	// edits to a file that address the diagnostic.
+	// TODO(matloob): Should multiple SuggestedFixes be allowed for a diagnostic?
+	// Diagnostics should not contain SuggestedFixes that overlap.
+	// Experimental: This API is experimental and may change in the future.
+	SuggestedFixes []SuggestedFix // optional
+}
+
+// A SuggestedFix is a code change associated with a Diagnostic that a user can choose
+// to apply to their code. Usually the SuggestedFix is meant to fix the issue flagged
+// by the diagnostic.
+// TextEdits for a SuggestedFix should not overlap. TextEdits for a SuggestedFix
+// should not contain edits for other packages.
+// Experimental: This API is experimental and may change in the future.
+type SuggestedFix struct {
+	// A description for this suggested fix to be shown to a user deciding
+	// whether to accept it.
+	Message   string
+	TextEdits []TextEdit
+}
+
+// A TextEdit represents the replacement of the code between Pos and End with the new text.
+// Each TextEdit should apply to a single file. End should not be earlier in the file than Pos.
+// Experimental: This API is experimental and may change in the future.
+type TextEdit struct {
+	// For a pure insertion, End can either be set to Pos or token.NoPos.
+	Pos     token.Pos
+	End     token.Pos
+	NewText []byte
+}

vendor/golang.org/x/tools/go/analysis/passes/cgocall/cgocall.go

@@ -107,7 +107,7 @@ func checkCgo(fset *token.FileSet, f *ast.File, info *types.Info, reportf func(t
 // cgo files of a package (those that import "C"). Such files are not
 // Go, so there may be gaps in type information around C.f references.
 //
-// This checker was initially written in vet to inpect raw cgo source
+// This checker was initially written in vet to inspect raw cgo source
 // files using partial type information. However, Analyzers in the new
 // analysis API are presented with the type-checked, "cooked" Go ASTs
 // resulting from cgo-processing files, so we must choose between
@@ -133,7 +133,7 @@ func checkCgo(fset *token.FileSet, f *ast.File, info *types.Info, reportf func(t
 //	func (T) f(int) string { ... }
 //
 // we synthesize a new ast.File, shown below, that dot-imports the
-// orginal "cooked" package using a special name ("·this·"), so that all
+// original "cooked" package using a special name ("·this·"), so that all
 // references to package members resolve correctly. (References to
 // unexported names cause an "unexported" error, which we ignore.)
 //

vendor/golang.org/x/tools/go/analysis/passes/composite/whitelist.go

@@ -24,6 +24,7 @@ var unkeyedLiteral = map[string]bool{
 	"image.Uniform":       true,
 
 	"unicode.Range16": true,
+	"unicode.Range32": true,
 
 	// These three structs are used in generated test main files,
 	// but the generator can be trusted.

vendor/golang.org/x/tools/go/analysis/passes/ctrlflow/ctrlflow.go

@@ -102,10 +102,11 @@ func run(pass *analysis.Pass) (interface{}, error) {
 	inspect.Preorder(nodeFilter, func(n ast.Node) {
 		switch n := n.(type) {
 		case *ast.FuncDecl:
-			fn := pass.TypesInfo.Defs[n.Name].(*types.Func)
+			// Type information may be incomplete.
-			funcDecls[fn] = &declInfo{decl: n}
+			if fn, ok := pass.TypesInfo.Defs[n.Name].(*types.Func); ok {
-			decls = append(decls, fn)
+				funcDecls[fn] = &declInfo{decl: n}
-
+				decls = append(decls, fn)
+			}
 		case *ast.FuncLit:
 			funcLits[n] = new(litInfo)
 			lits = append(lits, n)

vendor/golang.org/x/tools/go/analysis/passes/printf/printf.go

@@ -67,15 +67,20 @@ of arguments with no format string.
 `
 
 // isWrapper is a fact indicating that a function is a print or printf wrapper.
-type isWrapper struct{ Printf bool }
+type isWrapper struct{ Kind funcKind }
 
 func (f *isWrapper) AFact() {}
 
 func (f *isWrapper) String() string {
-	if f.Printf {
+	switch f.Kind {
+	case kindPrintf:
 		return "printfWrapper"
-	} else {
+	case kindPrint:
 		return "printWrapper"
+	case kindErrorf:
+		return "errorfWrapper"
+	default:
+		return "unknownWrapper"
 	}
 }
 
@@ -112,7 +117,11 @@ func maybePrintfWrapper(info *types.Info, decl ast.Decl) *printfWrapper {
 	if !ok || fdecl.Body == nil {
 		return nil
 	}
-	fn := info.Defs[fdecl.Name].(*types.Func)
+	fn, ok := info.Defs[fdecl.Name].(*types.Func)
+	// Type information may be incomplete.
+	if !ok {
+		return nil
+	}
 
 	sig := fn.Type().(*types.Signature)
 	if !sig.Variadic() {
@@ -223,16 +232,20 @@ func match(info *types.Info, arg ast.Expr, param *types.Var) bool {
 	return ok && info.ObjectOf(id) == param
 }
 
+type funcKind int
+
 const (
-	kindPrintf = 1
+	kindUnknown funcKind = iota
-	kindPrint  = 2
+	kindPrintf           = iota
+	kindPrint
+	kindErrorf
 )
 
 // checkPrintfFwd checks that a printf-forwarding wrapper is forwarding correctly.
 // It diagnoses writing fmt.Printf(format, args) instead of fmt.Printf(format, args...).
-func checkPrintfFwd(pass *analysis.Pass, w *printfWrapper, call *ast.CallExpr, kind int) {
+func checkPrintfFwd(pass *analysis.Pass, w *printfWrapper, call *ast.CallExpr, kind funcKind) {
 	matched := kind == kindPrint ||
-		kind == kindPrintf && len(call.Args) >= 2 && match(pass.TypesInfo, call.Args[len(call.Args)-2], w.format)
+		kind != kindUnknown && len(call.Args) >= 2 && match(pass.TypesInfo, call.Args[len(call.Args)-2], w.format)
 	if !matched {
 		return
 	}
@@ -262,7 +275,7 @@ func checkPrintfFwd(pass *analysis.Pass, w *printfWrapper, call *ast.CallExpr, k
 	fn := w.obj
 	var fact isWrapper
 	if !pass.ImportObjectFact(fn, &fact) {
-		fact.Printf = kind == kindPrintf
+		fact.Kind = kind
 		pass.ExportObjectFact(fn, &fact)
 		for _, caller := range w.callers {
 			checkPrintfFwd(pass, caller.w, caller.call, kind)
@@ -414,42 +427,42 @@ func checkCall(pass *analysis.Pass) {
 		call := n.(*ast.CallExpr)
 		fn, kind := printfNameAndKind(pass, call)
 		switch kind {
-		case kindPrintf:
+		case kindPrintf, kindErrorf:
-			checkPrintf(pass, call, fn)
+			checkPrintf(pass, kind, call, fn)
 		case kindPrint:
 			checkPrint(pass, call, fn)
 		}
 	})
 }
 
-func printfNameAndKind(pass *analysis.Pass, call *ast.CallExpr) (fn *types.Func, kind int) {
+func printfNameAndKind(pass *analysis.Pass, call *ast.CallExpr) (fn *types.Func, kind funcKind) {
 	fn, _ = typeutil.Callee(pass.TypesInfo, call).(*types.Func)
 	if fn == nil {
 		return nil, 0
 	}
 
-	var fact isWrapper
-	if pass.ImportObjectFact(fn, &fact) {
-		if fact.Printf {
-			return fn, kindPrintf
-		} else {
-			return fn, kindPrint
-		}
-	}
-
 	_, ok := isPrint[fn.FullName()]
 	if !ok {
 		// Next look up just "printf", for use with -printf.funcs.
 		_, ok = isPrint[strings.ToLower(fn.Name())]
 	}
 	if ok {
-		if strings.HasSuffix(fn.Name(), "f") {
+		if fn.Name() == "Errorf" {
+			kind = kindErrorf
+		} else if strings.HasSuffix(fn.Name(), "f") {
 			kind = kindPrintf
 		} else {
 			kind = kindPrint
 		}
+		return fn, kind
 	}
-	return fn, kind
+
+	var fact isWrapper
+	if pass.ImportObjectFact(fn, &fact) {
+		return fn, fact.Kind
+	}
+
+	return fn, kindUnknown
 }
 
 // isFormatter reports whether t satisfies fmt.Formatter.
@@ -491,7 +504,7 @@ type formatState struct {
 }
 
 // checkPrintf checks a call to a formatted print routine such as Printf.
-func checkPrintf(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
+func checkPrintf(pass *analysis.Pass, kind funcKind, call *ast.CallExpr, fn *types.Func) {
 	format, idx := formatString(pass, call)
 	if idx < 0 {
 		if false {
@@ -511,6 +524,7 @@ func checkPrintf(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
 	argNum := firstArg
 	maxArgNum := firstArg
 	anyIndex := false
+	anyW := false
 	for i, w := 0, 0; i < len(format); i += w {
 		w = 1
 		if format[i] != '%' {
@@ -527,6 +541,17 @@ func checkPrintf(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
 		if state.hasIndex {
 			anyIndex = true
 		}
+		if state.verb == 'w' {
+			if kind != kindErrorf {
+				pass.Reportf(call.Pos(), "%s call has error-wrapping directive %%w", state.name)
+				return
+			}
+			if anyW {
+				pass.Reportf(call.Pos(), "%s call has more than one error-wrapping directive %%w", state.name)
+				return
+			}
+			anyW = true
+		}
 		if len(state.argNums) > 0 {
 			// Continue with the next sequential argument.
 			argNum = state.argNums[len(state.argNums)-1] + 1
@@ -697,6 +722,7 @@ const (
 	argFloat
 	argComplex
 	argPointer
+	argError
 	anyType printfArgType = ^0
 )
 
@@ -739,7 +765,7 @@ var printVerbs = []printVerb{
 	{'T', "-", anyType},
 	{'U', "-#", argRune | argInt},
 	{'v', allFlags, anyType},
-	{'w', noFlag, anyType},
+	{'w', allFlags, argError},
 	{'x', sharpNumFlag, argRune | argInt | argString | argPointer},
 	{'X', sharpNumFlag, argRune | argInt | argString | argPointer},
 }

vendor/golang.org/x/tools/go/analysis/passes/printf/types.go

@@ -37,6 +37,12 @@ func matchArgTypeInternal(pass *analysis.Pass, t printfArgType, typ types.Type,
 			return true // probably a type check problem
 		}
 	}
+
+	// %w accepts only errors.
+	if t == argError {
+		return types.ConvertibleTo(typ, errorType)
+	}
+
 	// If the type implements fmt.Formatter, we have nothing to check.
 	if isFormatter(typ) {
 		return true

vendor/golang.org/x/tools/go/analysis/passes/structtag/structtag.go

@@ -40,8 +40,12 @@ func run(pass *analysis.Pass) (interface{}, error) {
 		(*ast.StructType)(nil),
 	}
 	inspect.Preorder(nodeFilter, func(n ast.Node) {
-		styp := pass.TypesInfo.Types[n.(*ast.StructType)].Type.(*types.Struct)
+		styp, ok := pass.TypesInfo.Types[n.(*ast.StructType)].Type.(*types.Struct)
-		var seen map[[2]string]token.Pos
+		// Type information may be incomplete.
+		if !ok {
+			return
+		}
+		var seen namesSeen
 		for i := 0; i < styp.NumFields(); i++ {
 			field := styp.Field(i)
 			tag := styp.Tag(i)
@@ -51,11 +55,38 @@ func run(pass *analysis.Pass) (interface{}, error) {
 	return nil, nil
 }
 
+// namesSeen keeps track of encoding tags by their key, name, and nested level
+// from the initial struct. The level is taken into account because equal
+// encoding key names only conflict when at the same level; otherwise, the lower
+// level shadows the higher level.
+type namesSeen map[uniqueName]token.Pos
+
+type uniqueName struct {
+	key   string // "xml" or "json"
+	name  string // the encoding name
+	level int    // anonymous struct nesting level
+}
+
+func (s *namesSeen) Get(key, name string, level int) (token.Pos, bool) {
+	if *s == nil {
+		*s = make(map[uniqueName]token.Pos)
+	}
+	pos, ok := (*s)[uniqueName{key, name, level}]
+	return pos, ok
+}
+
+func (s *namesSeen) Set(key, name string, level int, pos token.Pos) {
+	if *s == nil {
+		*s = make(map[uniqueName]token.Pos)
+	}
+	(*s)[uniqueName{key, name, level}] = pos
+}
+
 var checkTagDups = []string{"json", "xml"}
 var checkTagSpaces = map[string]bool{"json": true, "xml": true, "asn1": true}
 
 // checkCanonicalFieldTag checks a single struct field tag.
-func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, seen *map[[2]string]token.Pos) {
+func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, seen *namesSeen) {
 	switch pass.Pkg.Path() {
 	case "encoding/json", "encoding/xml":
 		// These packages know how to use their own APIs.
@@ -64,7 +95,7 @@ func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, s
 	}
 
 	for _, key := range checkTagDups {
-		checkTagDuplicates(pass, tag, key, field, field, seen)
+		checkTagDuplicates(pass, tag, key, field, field, seen, 1)
 	}
 
 	if err := validateStructTag(tag); err != nil {
@@ -95,28 +126,29 @@ func checkCanonicalFieldTag(pass *analysis.Pass, field *types.Var, tag string, s
 // checkTagDuplicates checks a single struct field tag to see if any tags are
 // duplicated. nearest is the field that's closest to the field being checked,
 // while still being part of the top-level struct type.
-func checkTagDuplicates(pass *analysis.Pass, tag, key string, nearest, field *types.Var, seen *map[[2]string]token.Pos) {
+func checkTagDuplicates(pass *analysis.Pass, tag, key string, nearest, field *types.Var, seen *namesSeen, level int) {
 	val := reflect.StructTag(tag).Get(key)
 	if val == "-" {
 		// Ignored, even if the field is anonymous.
 		return
 	}
 	if val == "" || val[0] == ',' {
-		if field.Anonymous() {
+		if !field.Anonymous() {
-			typ, ok := field.Type().Underlying().(*types.Struct)
+			// Ignored if the field isn't anonymous.
-			if !ok {
+			return
-				return
+		}
-			}
+		typ, ok := field.Type().Underlying().(*types.Struct)
-			for i := 0; i < typ.NumFields(); i++ {
+		if !ok {
-				field := typ.Field(i)
+			return
-				if !field.Exported() {
+		}
-					continue
+		for i := 0; i < typ.NumFields(); i++ {
-				}
+			field := typ.Field(i)
-				tag := typ.Tag(i)
+			if !field.Exported() {
-				checkTagDuplicates(pass, tag, key, nearest, field, seen)
+				continue
-			}
+			}
+			tag := typ.Tag(i)
+			checkTagDuplicates(pass, tag, key, nearest, field, seen, level+1)
 		}
-		// Ignored if the field isn't anonymous.
 		return
 	}
 	if key == "xml" && field.Name() == "XMLName" {
@@ -139,10 +171,7 @@ func checkTagDuplicates(pass *analysis.Pass, tag, key string, nearest, field *ty
 		}
 		val = val[:i]
 	}
-	if *seen == nil {
+	if pos, ok := seen.Get(key, val, level); ok {
-		*seen = map[[2]string]token.Pos{}
-	}
-	if pos, ok := (*seen)[[2]string{key, val}]; ok {
 		alsoPos := pass.Fset.Position(pos)
 		alsoPos.Column = 0
 
@@ -161,7 +190,7 @@ func checkTagDuplicates(pass *analysis.Pass, tag, key string, nearest, field *ty
 
 		pass.Reportf(nearest.Pos(), "struct field %s repeats %s tag %q also at %s", field.Name(), key, val, alsoPos)
 	} else {
-		(*seen)[[2]string{key, val}] = field.Pos()
+		seen.Set(key, val, level, field.Pos())
 	}
 }
 

vendor/golang.org/x/tools/go/analysis/passes/tests/tests.go

@@ -20,7 +20,10 @@ const Doc = `check for common mistaken usages of tests and examples
 
 The tests checker walks Test, Benchmark and Example functions checking
 malformed names, wrong signatures and examples documenting non-existent
-identifiers.`
+identifiers.
+
+Please see the documentation for package testing in golang.org/pkg/testing
+for the conventions that are enforced for Tests, Benchmarks, and Examples.`
 
 var Analyzer = &analysis.Analyzer{
 	Name: "tests",

vendor/golang.org/x/tools/go/analysis/validate.go

@@ -10,7 +10,7 @@ import (
 // Checks include:
 // that the name is a valid identifier;
 // that analyzer names are unique;
-// that the Requires graph is acylic;
+// that the Requires graph is acyclic;
 // that analyzer fact types are unique;
 // that each fact type is a pointer.
 func Validate(analyzers []*Analyzer) error {

vendor/golang.org/x/tools/go/cfg/builder.go

@@ -149,7 +149,7 @@ func (b *builder) branchStmt(s *ast.BranchStmt) {
 		}
 
 	case token.FALLTHROUGH:
-		for t := b.targets; t != nil; t = t.tail {
+		for t := b.targets; t != nil && block == nil; t = t.tail {
 			block = t._fallthrough
 		}
 

vendor/golang.org/x/tools/go/internal/gcimporter/bimport.go

@@ -976,10 +976,11 @@ const (
 	aliasTag
 )
 
+var predeclOnce sync.Once
 var predecl []types.Type // initialized lazily
 
 func predeclared() []types.Type {
-	if predecl == nil {
+	predeclOnce.Do(func() {
 		// initialize lazily to be sure that all
 		// elements have been initialized before
 		predecl = []types.Type{ // basic types
@@ -1026,7 +1027,7 @@ func predeclared() []types.Type {
 			// used internally by gc; never used by this package or in .a files
 			anyType{},
 		}
-	}
+	})
 	return predecl
 }
 

vendor/golang.org/x/tools/go/internal/packagesdriver/sizes.go

@@ -82,15 +82,28 @@ func GetSizesGolist(ctx context.Context, buildFlags, env []string, dir string, u
 	args = append(args, buildFlags...)
 	args = append(args, "--", "unsafe")
 	stdout, err := InvokeGo(ctx, env, dir, usesExportData, args...)
+	var goarch, compiler string
 	if err != nil {
-		return nil, err
+		if strings.Contains(err.Error(), "cannot find main module") {
+			// User's running outside of a module. All bets are off. Get GOARCH and guess compiler is gc.
+			// TODO(matloob): Is this a problem in practice?
+			envout, enverr := InvokeGo(ctx, env, dir, usesExportData, "env", "GOARCH")
+			if enverr != nil {
+				return nil, err
+			}
+			goarch = strings.TrimSpace(envout.String())
+			compiler = "gc"
+		} else {
+			return nil, err
+		}
+	} else {
+		fields := strings.Fields(stdout.String())
+		if len(fields) < 2 {
+			return nil, fmt.Errorf("could not determine GOARCH and Go compiler")
+		}
+		goarch = fields[0]
+		compiler = fields[1]
 	}
-	fields := strings.Fields(stdout.String())
-	if len(fields) < 2 {
-		return nil, fmt.Errorf("could not determine GOARCH and Go compiler")
-	}
-	goarch := fields[0]
-	compiler := fields[1]
 	return types.SizesFor(compiler, goarch), nil
 }
 

vendor/golang.org/x/tools/go/loader/doc.go

@@ -7,7 +7,8 @@
 // of dependencies.  The ASTs and the derived facts are retained for
 // later use.
 //
-// THIS INTERFACE IS EXPERIMENTAL AND IS LIKELY TO CHANGE.
+// Deprecated: This is an older API and does not have support
+// for modules. Use golang.org/x/tools/go/packages instead.
 //
 // The package defines two primary types: Config, which specifies a
 // set of initial packages to load and various other options; and
@@ -201,5 +202,3 @@ package loader
 // the error.
 //
 // The result of using concurrency is about a 2.5x speedup for stdlib_test.
-
-// TODO(adonovan): overhaul the package documentation.

vendor/golang.org/x/tools/go/loader/loader.go

@@ -811,7 +811,15 @@ func (imp *importer) doImport(from *PackageInfo, to string) (*types.Package, err
 	// Import of incomplete package: this indicates a cycle.
 	fromPath := from.Pkg.Path()
 	if cycle := imp.findPath(path, fromPath); cycle != nil {
-		cycle = append([]string{fromPath}, cycle...)
+		// Normalize cycle: start from alphabetically largest node.
+		pos, start := -1, ""
+		for i, s := range cycle {
+			if pos < 0 || s > start {
+				pos, start = i, s
+			}
+		}
+		cycle = append(cycle, cycle[:pos]...)[pos:] // rotate cycle to start from largest
+		cycle = append(cycle, cycle[0])             // add start node to end to show cycliness
 		return nil, fmt.Errorf("import cycle: %s", strings.Join(cycle, " -> "))
 	}
 

vendor/golang.org/x/tools/go/packages/external.go

@@ -16,14 +16,29 @@ import (
 	"strings"
 )
 
-// Driver
+// The Driver Protocol
+//
+// The driver, given the inputs to a call to Load, returns metadata about the packages specified.
+// This allows for different build systems to support go/packages by telling go/packages how the
+// packages' source is organized.
+// The driver is a binary, either specified by the GOPACKAGESDRIVER environment variable or in
+// the path as gopackagesdriver. It's given the inputs to load in its argv. See the package
+// documentation in doc.go for the full description of the patterns that need to be supported.
+// A driver receives as a JSON-serialized driverRequest struct in standard input and will
+// produce a JSON-serialized driverResponse (see definition in packages.go) in its standard output.
+
+// driverRequest is used to provide the portion of Load's Config that is needed by a driver.
 type driverRequest struct {
-	Command    string            `json:"command"`
+	Mode LoadMode `json:"mode"`
-	Mode       LoadMode          `json:"mode"`
+	// Env specifies the environment the underlying build system should be run in.
-	Env        []string          `json:"env"`
+	Env []string `json:"env"`
-	BuildFlags []string          `json:"build_flags"`
+	// BuildFlags are flags that should be passed to the underlying build system.
-	Tests      bool              `json:"tests"`
+	BuildFlags []string `json:"build_flags"`
-	Overlay    map[string][]byte `json:"overlay"`
+	// Tests specifies whether the patterns should also return test packages.
+	Tests bool `json:"tests"`
+	// Overlay maps file paths (relative to the driver's working directory) to the byte contents
+	// of overlay files.
+	Overlay map[string][]byte `json:"overlay"`
 }
 
 // findExternalDriver returns the file path of a tool that supplies

vendor/golang.org/x/tools/go/packages/golist.go

@@ -13,6 +13,7 @@ import (
 	"log"
 	"os"
 	"os/exec"
+	"path"
 	"path/filepath"
 	"reflect"
 	"regexp"
@@ -71,6 +72,28 @@ func (r *responseDeduper) addRoot(id string) {
 	r.dr.Roots = append(r.dr.Roots, id)
 }
 
+// goInfo contains global information from the go tool.
+type goInfo struct {
+	rootDirs map[string]string
+	env      goEnv
+}
+
+type goEnv struct {
+	modulesOn bool
+}
+
+func determineEnv(cfg *Config) goEnv {
+	buf, err := invokeGo(cfg, "env", "GOMOD")
+	if err != nil {
+		return goEnv{}
+	}
+	gomod := bytes.TrimSpace(buf.Bytes())
+
+	env := goEnv{}
+	env.modulesOn = len(gomod) > 0
+	return env
+}
+
 // goListDriver uses the go list command to interpret the patterns and produce
 // the build system package structure.
 // See driver for more details.
@@ -86,6 +109,28 @@ func goListDriver(cfg *Config, patterns ...string) (*driverResponse, error) {
 		}()
 	}
 
+	// start fetching rootDirs
+	var info goInfo
+	var rootDirsReady, envReady = make(chan struct{}), make(chan struct{})
+	go func() {
+		info.rootDirs = determineRootDirs(cfg)
+		close(rootDirsReady)
+	}()
+	go func() {
+		info.env = determineEnv(cfg)
+		close(envReady)
+	}()
+	getGoInfo := func() *goInfo {
+		<-rootDirsReady
+		<-envReady
+		return &info
+	}
+
+	// always pass getGoInfo to golistDriver
+	golistDriver := func(cfg *Config, patterns ...string) (*driverResponse, error) {
+		return golistDriver(cfg, getGoInfo, patterns...)
+	}
+
 	// Determine files requested in contains patterns
 	var containFiles []string
 	var packagesNamed []string
@@ -147,7 +192,7 @@ extractQueries:
 	var containsCandidates []string
 
 	if len(containFiles) != 0 {
-		if err := runContainsQueries(cfg, golistDriver, response, containFiles); err != nil {
+		if err := runContainsQueries(cfg, golistDriver, response, containFiles, getGoInfo); err != nil {
 			return nil, err
 		}
 	}
@@ -158,7 +203,7 @@ extractQueries:
 		}
 	}
 
-	modifiedPkgs, needPkgs, err := processGolistOverlay(cfg, response.dr)
+	modifiedPkgs, needPkgs, err := processGolistOverlay(cfg, response, getGoInfo)
 	if err != nil {
 		return nil, err
 	}
@@ -166,13 +211,25 @@ extractQueries:
 		containsCandidates = append(containsCandidates, modifiedPkgs...)
 		containsCandidates = append(containsCandidates, needPkgs...)
 	}
-	if err := addNeededOverlayPackages(cfg, golistDriver, response, needPkgs); err != nil {
+	if err := addNeededOverlayPackages(cfg, golistDriver, response, needPkgs, getGoInfo); err != nil {
 		return nil, err
 	}
 	// Check candidate packages for containFiles.
 	if len(containFiles) > 0 {
 		for _, id := range containsCandidates {
-			pkg := response.seenPackages[id]
+			pkg, ok := response.seenPackages[id]
+			if !ok {
+				response.addPackage(&Package{
+					ID: id,
+					Errors: []Error{
+						{
+							Kind: ListError,
+							Msg:  fmt.Sprintf("package %s expected but not seen", id),
+						},
+					},
+				})
+				continue
+			}
 			for _, f := range containFiles {
 				for _, g := range pkg.GoFiles {
 					if sameFile(f, g) {
@@ -186,26 +243,33 @@ extractQueries:
 	return response.dr, nil
 }
 
-func addNeededOverlayPackages(cfg *Config, driver driver, response *responseDeduper, pkgs []string) error {
+func addNeededOverlayPackages(cfg *Config, driver driver, response *responseDeduper, pkgs []string, getGoInfo func() *goInfo) error {
 	if len(pkgs) == 0 {
 		return nil
 	}
-	dr, err := driver(cfg, pkgs...)
+	drivercfg := *cfg
+	if getGoInfo().env.modulesOn {
+		drivercfg.BuildFlags = append(drivercfg.BuildFlags, "-mod=readonly")
+	}
+	dr, err := driver(&drivercfg, pkgs...)
+
 	if err != nil {
 		return err
 	}
 	for _, pkg := range dr.Packages {
 		response.addPackage(pkg)
 	}
-	_, needPkgs, err := processGolistOverlay(cfg, response.dr)
+	_, needPkgs, err := processGolistOverlay(cfg, response, getGoInfo)
 	if err != nil {
 		return err
 	}
-	addNeededOverlayPackages(cfg, driver, response, needPkgs)
+	if err := addNeededOverlayPackages(cfg, driver, response, needPkgs, getGoInfo); err != nil {
+		return err
+	}
 	return nil
 }
 
-func runContainsQueries(cfg *Config, driver driver, response *responseDeduper, queries []string) error {
+func runContainsQueries(cfg *Config, driver driver, response *responseDeduper, queries []string, goInfo func() *goInfo) error {
 	for _, query := range queries {
 		// TODO(matloob): Do only one query per directory.
 		fdir := filepath.Dir(query)
@@ -216,8 +280,31 @@ func runContainsQueries(cfg *Config, driver driver, response *responseDeduper, q
 			return fmt.Errorf("could not determine absolute path of file= query path %q: %v", query, err)
 		}
 		dirResponse, err := driver(cfg, pattern)
-		if err != nil {
+		if err != nil || (len(dirResponse.Packages) == 1 && len(dirResponse.Packages[0].Errors) == 1) {
-			return err
+			// There was an error loading the package. Try to load the file as an ad-hoc package.
+			// Usually the error will appear in a returned package, but may not if we're in modules mode
+			// and the ad-hoc is located outside a module.
+			var queryErr error
+			dirResponse, queryErr = driver(cfg, query)
+			if queryErr != nil {
+				// Return the original error if the attempt to fall back failed.
+				return err
+			}
+			// Special case to handle issue #33482:
+			// If this is a file= query for ad-hoc packages where the file only exists on an overlay,
+			// and exists outside of a module, add the file in for the package.
+			if len(dirResponse.Packages) == 1 && len(dirResponse.Packages) == 1 &&
+				dirResponse.Packages[0].ID == "command-line-arguments" && len(dirResponse.Packages[0].GoFiles) == 0 {
+				filename := filepath.Join(pattern, filepath.Base(query)) // avoid recomputing abspath
+				// TODO(matloob): check if the file is outside of a root dir?
+				for path := range cfg.Overlay {
+					if path == filename {
+						dirResponse.Packages[0].Errors = nil
+						dirResponse.Packages[0].GoFiles = []string{path}
+						dirResponse.Packages[0].CompiledGoFiles = []string{path}
+					}
+				}
+			}
 		}
 		isRoot := make(map[string]bool, len(dirResponse.Roots))
 		for _, root := range dirResponse.Roots {
@@ -294,9 +381,7 @@ func runNamedQueries(cfg *Config, driver driver, response *responseDeduper, quer
 
 	startWalk := time.Now()
 	gopathwalk.Walk(roots, add, gopathwalk.Options{ModulesEnabled: modRoot != "", Debug: debug})
-	if debug {
+	cfg.Logf("%v for walk", time.Since(startWalk))
-		log.Printf("%v for walk", time.Since(startWalk))
-	}
 
 	// Weird special case: the top-level package in a module will be in
 	// whatever directory the user checked the repository out into. It's
@@ -547,7 +632,7 @@ func otherFiles(p *jsonPackage) [][]string {
 // golistDriver uses the "go list" command to expand the pattern
 // words and return metadata for the specified packages. dir may be
 // "" and env may be nil, as per os/exec.Command.
-func golistDriver(cfg *Config, words ...string) (*driverResponse, error) {
+func golistDriver(cfg *Config, rootsDirs func() *goInfo, words ...string) (*driverResponse, error) {
 	// go list uses the following identifiers in ImportPath and Imports:
 	//
 	// 	"p"			-- importable package or main (command)
@@ -588,6 +673,20 @@ func golistDriver(cfg *Config, words ...string) (*driverResponse, error) {
 			return nil, fmt.Errorf("package missing import path: %+v", p)
 		}
 
+		// Work around https://golang.org/issue/33157:
+		// go list -e, when given an absolute path, will find the package contained at
+		// that directory. But when no package exists there, it will return a fake package
+		// with an error and the ImportPath set to the absolute path provided to go list.
+		// Try toto convert that absolute path to what its package path would be if it's
+		// contained in a known module or GOPATH entry. This will allow the package to be
+		// properly "reclaimed" when overlays are processed.
+		if filepath.IsAbs(p.ImportPath) && p.Error != nil {
+			pkgPath, ok := getPkgPath(p.ImportPath, rootsDirs)
+			if ok {
+				p.ImportPath = pkgPath
+			}
+		}
+
 		if old, found := seen[p.ImportPath]; found {
 			if !reflect.DeepEqual(p, old) {
 				return nil, fmt.Errorf("internal error: go list gives conflicting information for package %v", p.ImportPath)
@@ -681,7 +780,7 @@ func golistDriver(cfg *Config, words ...string) (*driverResponse, error) {
 		if p.Error != nil {
 			pkg.Errors = append(pkg.Errors, Error{
 				Pos: p.Error.Pos,
-				Msg: p.Error.Err,
+				Msg: strings.TrimSpace(p.Error.Err), // Trim to work around golang.org/issue/32363.
 			})
 		}
 
@@ -691,6 +790,27 @@ func golistDriver(cfg *Config, words ...string) (*driverResponse, error) {
 	return &response, nil
 }
 
+// getPkgPath finds the package path of a directory if it's relative to a root directory.
+func getPkgPath(dir string, goInfo func() *goInfo) (string, bool) {
+	for rdir, rpath := range goInfo().rootDirs {
+		// TODO(matloob): This doesn't properly handle symlinks.
+		r, err := filepath.Rel(rdir, dir)
+		if err != nil {
+			continue
+		}
+		if rpath != "" {
+			// We choose only ore root even though the directory even it can belong in multiple modules
+			// or GOPATH entries. This is okay because we only need to work with absolute dirs when a
+			// file is missing from disk, for instance when gopls calls go/packages in an overlay.
+			// Once the file is saved, gopls, or the next invocation of the tool will get the correct
+			// result straight from golist.
+			// TODO(matloob): Implement module tiebreaking?
+			return path.Join(rpath, filepath.ToSlash(r)), true
+		}
+	}
+	return "", false
+}
+
 // absJoin absolutizes and flattens the lists of files.
 func absJoin(dir string, fileses ...[]string) (res []string) {
 	for _, files := range fileses {
@@ -711,7 +831,7 @@ func golistargs(cfg *Config, words []string) []string {
 		fmt.Sprintf("-compiled=%t", cfg.Mode&(NeedCompiledGoFiles|NeedSyntax|NeedTypesInfo|NeedTypesSizes) != 0),
 		fmt.Sprintf("-test=%t", cfg.Tests),
 		fmt.Sprintf("-export=%t", usesExportData(cfg)),
-		fmt.Sprintf("-deps=%t", cfg.Mode&NeedDeps != 0),
+		fmt.Sprintf("-deps=%t", cfg.Mode&NeedImports != 0),
 		// go list doesn't let you pass -test and -find together,
 		// probably because you'd just get the TestMain.
 		fmt.Sprintf("-find=%t", !cfg.Tests && cfg.Mode&findFlags == 0),
@@ -737,11 +857,9 @@ func invokeGo(cfg *Config, args ...string) (*bytes.Buffer, error) {
 	cmd.Dir = cfg.Dir
 	cmd.Stdout = stdout
 	cmd.Stderr = stderr
-	if debug {
+	defer func(start time.Time) {
-		defer func(start time.Time) {
+		cfg.Logf("%s for %v, stderr: <<%s>>\n", time.Since(start), cmdDebugStr(cmd, args...), stderr)
-			log.Printf("%s for %v, stderr: <<%s>>\n", time.Since(start), cmdDebugStr(cmd, args...), stderr)
+	}(time.Now())
-		}(time.Now())
-	}
 
 	if err := cmd.Run(); err != nil {
 		// Check for 'go' executable not being found.
@@ -761,6 +879,19 @@ func invokeGo(cfg *Config, args ...string) (*bytes.Buffer, error) {
 			return nil, goTooOldError{fmt.Errorf("unsupported version of go: %s: %s", exitErr, stderr)}
 		}
 
+		// Related to #24854
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "unexpected directory layout") {
+			return nil, fmt.Errorf("%s", stderr.String())
+		}
+
+		// Is there an error running the C compiler in cgo? This will be reported in the "Error" field
+		// and should be suppressed by go list -e.
+		//
+		// This condition is not perfect yet because the error message can include other error messages than runtime/cgo.
+		if len(stderr.String()) > 0 && strings.HasPrefix(stderr.String(), "# runtime/cgo\n") {
+			return stdout, nil
+		}
+
 		// This error only appears in stderr. See golang.org/cl/166398 for a fix in go list to show
 		// the error in the Err section of stdout in case -e option is provided.
 		// This fix is provided for backwards compatibility.
@@ -770,13 +901,49 @@ func invokeGo(cfg *Config, args ...string) (*bytes.Buffer, error) {
 			return bytes.NewBufferString(output), nil
 		}
 
+		// Similar to the previous error, but currently lacks a fix in Go.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "named files must all be in one directory") {
+			output := fmt.Sprintf(`{"ImportPath": "command-line-arguments","Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
+		// Backwards compatibility for Go 1.11 because 1.12 and 1.13 put the directory in the ImportPath.
+		// If the package doesn't exist, put the absolute path of the directory into the error message,
+		// as Go 1.13 list does.
+		const noSuchDirectory = "no such directory"
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), noSuchDirectory) {
+			errstr := stderr.String()
+			abspath := strings.TrimSpace(errstr[strings.Index(errstr, noSuchDirectory)+len(noSuchDirectory):])
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				abspath, strings.Trim(stderr.String(), "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
 		// Workaround for #29280: go list -e has incorrect behavior when an ad-hoc package doesn't exist.
+		// Note that the error message we look for in this case is different that the one looked for above.
 		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "no such file or directory") {
 			output := fmt.Sprintf(`{"ImportPath": "command-line-arguments","Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
 				strings.Trim(stderr.String(), "\n"))
 			return bytes.NewBufferString(output), nil
 		}
 
+		// Workaround for an instance of golang.org/issue/26755: go list -e  will return a non-zero exit
+		// status if there's a dependency on a package that doesn't exist. But it should return
+		// a zero exit status and set an error on that package.
+		if len(stderr.String()) > 0 && strings.Contains(stderr.String(), "no Go files in") {
+			// try to extract package name from string
+			stderrStr := stderr.String()
+			var importPath string
+			colon := strings.Index(stderrStr, ":")
+			if colon > 0 && strings.HasPrefix(stderrStr, "go build ") {
+				importPath = stderrStr[len("go build "):colon]
+			}
+			output := fmt.Sprintf(`{"ImportPath": %q,"Incomplete": true,"Error": {"Pos": "","Err": %q}}`,
+				importPath, strings.Trim(stderrStr, "\n"))
+			return bytes.NewBufferString(output), nil
+		}
+
 		// Export mode entails a build.
 		// If that build fails, errors appear on stderr
 		// (despite the -e flag) and the Export field is blank.

vendor/golang.org/x/tools/go/packages/golist_overlay.go

@@ -1,8 +1,12 @@
 package packages
 
 import (
+	"bytes"
+	"encoding/json"
+	"fmt"
 	"go/parser"
 	"go/token"
+	"path"
 	"path/filepath"
 	"strconv"
 	"strings"
@@ -12,74 +16,167 @@ import (
 // files that don't exist on disk to an overlay. The results can be
 // sometimes incorrect.
 // TODO(matloob): Handle unsupported cases, including the following:
-// - test files
-// - adding test and non-test files to test variants of packages
 // - determining the correct package to add given a new import path
-// - creating packages that don't exist
+func processGolistOverlay(cfg *Config, response *responseDeduper, rootDirs func() *goInfo) (modifiedPkgs, needPkgs []string, err error) {
-func processGolistOverlay(cfg *Config, response *driverResponse) (modifiedPkgs, needPkgs []string, err error) {
 	havePkgs := make(map[string]string) // importPath -> non-test package ID
 	needPkgsSet := make(map[string]bool)
 	modifiedPkgsSet := make(map[string]bool)
 
-	for _, pkg := range response.Packages {
+	for _, pkg := range response.dr.Packages {
 		// This is an approximation of import path to id. This can be
 		// wrong for tests, vendored packages, and a number of other cases.
 		havePkgs[pkg.PkgPath] = pkg.ID
 	}
 
-outer:
+	// If no new imports are added, it is safe to avoid loading any needPkgs.
-	for path, contents := range cfg.Overlay {
+	// Otherwise, it's hard to tell which package is actually being loaded
-		base := filepath.Base(path)
+	// (due to vendoring) and whether any modified package will show up
-		if strings.HasSuffix(path, "_test.go") {
+	// in the transitive set of dependencies (because new imports are added,
-			// Overlays don't support adding new test files yet.
+	// potentially modifying the transitive set of dependencies).
-			// TODO(matloob): support adding new test files.
+	var overlayAddsImports bool
+
+	for opath, contents := range cfg.Overlay {
+		base := filepath.Base(opath)
+		dir := filepath.Dir(opath)
+		var pkg *Package
+		var testVariantOf *Package // if opath is a test file, this is the package it is testing
+		var fileExists bool
+		isTest := strings.HasSuffix(opath, "_test.go")
+		pkgName, ok := extractPackageName(opath, contents)
+		if !ok {
+			// Don't bother adding a file that doesn't even have a parsable package statement
+			// to the overlay.
 			continue
 		}
-		dir := filepath.Dir(path)
+	nextPackage:
-		for _, pkg := range response.Packages {
+		for _, p := range response.dr.Packages {
-			var dirContains, fileExists bool
+			if pkgName != p.Name && p.ID != "command-line-arguments" {
-			for _, f := range pkg.GoFiles {
+				continue
-				if sameFile(filepath.Dir(f), dir) {
+			}
-					dirContains = true
+			for _, f := range p.GoFiles {
+				if !sameFile(filepath.Dir(f), dir) {
+					continue
 				}
+				if isTest && !hasTestFiles(p) {
+					// TODO(matloob): Are there packages other than the 'production' variant
+					// of a package that this can match? This shouldn't match the test main package
+					// because the file is generated in another directory.
+					testVariantOf = p
+					continue nextPackage
+				}
+				pkg = p
 				if filepath.Base(f) == base {
 					fileExists = true
 				}
 			}
-			// The overlay could have included an entirely new package.
+		}
-			isNewPackage := extractPackage(pkg, path, contents)
+		// The overlay could have included an entirely new package.
-			if dirContains || isNewPackage {
+		if pkg == nil {
-				if !fileExists {
+			// Try to find the module or gopath dir the file is contained in.
-					pkg.GoFiles = append(pkg.GoFiles, path) // TODO(matloob): should the file just be added to GoFiles?
+			// Then for modules, add the module opath to the beginning.
-					pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, path)
+			var pkgPath string
-					modifiedPkgsSet[pkg.ID] = true
+			for rdir, rpath := range rootDirs().rootDirs {
-				}
+				// TODO(matloob): This doesn't properly handle symlinks.
-				imports, err := extractImports(path, contents)
+				r, err := filepath.Rel(rdir, dir)
 				if err != nil {
-					// Let the parser or type checker report errors later.
+					continue
-					continue outer
 				}
-				for _, imp := range imports {
+				pkgPath = filepath.ToSlash(r)
-					_, found := pkg.Imports[imp]
+				if rpath != "" {
-					if !found {
+					pkgPath = path.Join(rpath, pkgPath)
-						needPkgsSet[imp] = true
-						// TODO(matloob): Handle cases when the following block isn't correct.
-						// These include imports of test variants, imports of vendored packages, etc.
-						id, ok := havePkgs[imp]
-						if !ok {
-							id = imp
-						}
-						pkg.Imports[imp] = &Package{ID: id}
-					}
 				}
-				continue outer
+				// We only create one new package even it can belong in multiple modules or GOPATH entries.
+				// This is okay because tools (such as the LSP) that use overlays will recompute the overlay
+				// once the file is saved, and golist will do the right thing.
+				// TODO(matloob): Implement module tiebreaking?
+				break
+			}
+			if pkgPath == "" {
+				continue
+			}
+			isXTest := strings.HasSuffix(pkgName, "_test")
+			if isXTest {
+				pkgPath += "_test"
+			}
+			id := pkgPath
+			if isTest && !isXTest {
+				id = fmt.Sprintf("%s [%s.test]", pkgPath, pkgPath)
+			}
+			// Try to reclaim a package with the same id if it exists in the response.
+			for _, p := range response.dr.Packages {
+				if reclaimPackage(p, id, opath, contents) {
+					pkg = p
+					break
+				}
+			}
+			// Otherwise, create a new package
+			if pkg == nil {
+				pkg = &Package{PkgPath: pkgPath, ID: id, Name: pkgName, Imports: make(map[string]*Package)}
+				response.addPackage(pkg)
+				havePkgs[pkg.PkgPath] = id
+				// Add the production package's sources for a test variant.
+				if isTest && !isXTest && testVariantOf != nil {
+					pkg.GoFiles = append(pkg.GoFiles, testVariantOf.GoFiles...)
+					pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, testVariantOf.CompiledGoFiles...)
+				}
+			}
+		}
+		if !fileExists {
+			pkg.GoFiles = append(pkg.GoFiles, opath)
+			// TODO(matloob): Adding the file to CompiledGoFiles can exhibit the wrong behavior
+			// if the file will be ignored due to its build tags.
+			pkg.CompiledGoFiles = append(pkg.CompiledGoFiles, opath)
+			modifiedPkgsSet[pkg.ID] = true
+		}
+		imports, err := extractImports(opath, contents)
+		if err != nil {
+			// Let the parser or type checker report errors later.
+			continue
+		}
+		for _, imp := range imports {
+			_, found := pkg.Imports[imp]
+			if !found {
+				overlayAddsImports = true
+				// TODO(matloob): Handle cases when the following block isn't correct.
+				// These include imports of test variants, imports of vendored packages, etc.
+				id, ok := havePkgs[imp]
+				if !ok {
+					id = imp
+				}
+				pkg.Imports[imp] = &Package{ID: id}
+			}
+		}
+		continue
+	}
+
+	// toPkgPath tries to guess the package path given the id.
+	// This isn't always correct -- it's certainly wrong for
+	// vendored packages' paths.
+	toPkgPath := func(id string) string {
+		// TODO(matloob): Handle vendor paths.
+		i := strings.IndexByte(id, ' ')
+		if i >= 0 {
+			return id[:i]
+		}
+		return id
+	}
+
+	// Do another pass now that new packages have been created to determine the
+	// set of missing packages.
+	for _, pkg := range response.dr.Packages {
+		for _, imp := range pkg.Imports {
+			pkgPath := toPkgPath(imp.ID)
+			if _, ok := havePkgs[pkgPath]; !ok {
+				needPkgsSet[pkgPath] = true
 			}
 		}
 	}
 
-	needPkgs = make([]string, 0, len(needPkgsSet))
+	if overlayAddsImports {
-	for pkg := range needPkgsSet {
+		needPkgs = make([]string, 0, len(needPkgsSet))
-		needPkgs = append(needPkgs, pkg)
+		for pkg := range needPkgsSet {
+			needPkgs = append(needPkgs, pkg)
+		}
 	}
 	modifiedPkgs = make([]string, 0, len(modifiedPkgsSet))
 	for pkg := range modifiedPkgsSet {
@@ -88,6 +185,55 @@ outer:
 	return modifiedPkgs, needPkgs, err
 }
 
+func hasTestFiles(p *Package) bool {
+	for _, f := range p.GoFiles {
+		if strings.HasSuffix(f, "_test.go") {
+			return true
+		}
+	}
+	return false
+}
+
+// determineRootDirs returns a mapping from directories code can be contained in to the
+// corresponding import path prefixes of those directories.
+// Its result is used to try to determine the import path for a package containing
+// an overlay file.
+func determineRootDirs(cfg *Config) map[string]string {
+	// Assume modules first:
+	out, err := invokeGo(cfg, "list", "-m", "-json", "all")
+	if err != nil {
+		return determineRootDirsGOPATH(cfg)
+	}
+	m := map[string]string{}
+	type jsonMod struct{ Path, Dir string }
+	for dec := json.NewDecoder(out); dec.More(); {
+		mod := new(jsonMod)
+		if err := dec.Decode(mod); err != nil {
+			return m // Give up and return an empty map. Package won't be found for overlay.
+		}
+		if mod.Dir != "" && mod.Path != "" {
+			// This is a valid module; add it to the map.
+			m[mod.Dir] = mod.Path
+		}
+	}
+	return m
+}
+
+func determineRootDirsGOPATH(cfg *Config) map[string]string {
+	m := map[string]string{}
+	out, err := invokeGo(cfg, "env", "GOPATH")
+	if err != nil {
+		// Could not determine root dir mapping. Everything is best-effort, so just return an empty map.
+		// When we try to find the import path for a directory, there will be no root-dir match and
+		// we'll give up.
+		return m
+	}
+	for _, p := range filepath.SplitList(string(bytes.TrimSpace(out.Bytes()))) {
+		m[filepath.Join(p, "src")] = ""
+	}
+	return m
+}
+
 func extractImports(filename string, contents []byte) ([]string, error) {
 	f, err := parser.ParseFile(token.NewFileSet(), filename, contents, parser.ImportsOnly) // TODO(matloob): reuse fileset?
 	if err != nil {
@@ -105,13 +251,16 @@ func extractImports(filename string, contents []byte) ([]string, error) {
 	return res, nil
 }
 
-// extractPackage attempts to extract a package defined in an overlay.
+// reclaimPackage attempts to reuse a package that failed to load in an overlay.
 //
 // If the package has errors and has no Name, GoFiles, or Imports,
 // then it's possible that it doesn't yet exist on disk.
-func extractPackage(pkg *Package, filename string, contents []byte) bool {
+func reclaimPackage(pkg *Package, id string, filename string, contents []byte) bool {
 	// TODO(rstambler): Check the message of the actual error?
 	// It differs between $GOPATH and module mode.
+	if pkg.ID != id {
+		return false
+	}
 	if len(pkg.Errors) != 1 {
 		return false
 	}
@@ -124,15 +273,21 @@ func extractPackage(pkg *Package, filename string, contents []byte) bool {
 	if len(pkg.Imports) > 0 {
 		return false
 	}
-	f, err := parser.ParseFile(token.NewFileSet(), filename, contents, parser.PackageClauseOnly) // TODO(matloob): reuse fileset?
+	pkgName, ok := extractPackageName(filename, contents)
-	if err != nil {
+	if !ok {
 		return false
 	}
-	// TODO(rstambler): This doesn't work for main packages.
+	pkg.Name = pkgName
-	if filepath.Base(pkg.PkgPath) != f.Name.Name {
-		return false
-	}
-	pkg.Name = f.Name.Name
 	pkg.Errors = nil
 	return true
 }
+
+func extractPackageName(filename string, contents []byte) (string, bool) {
+	// TODO(rstambler): Check the message of the actual error?
+	// It differs between $GOPATH and module mode.
+	f, err := parser.ParseFile(token.NewFileSet(), filename, contents, parser.PackageClauseOnly) // TODO(matloob): reuse fileset?
+	if err != nil {
+		return "", false
+	}
+	return f.Name.Name, true
+}

vendor/golang.org/x/tools/go/packages/packages.go

@@ -25,24 +25,16 @@ import (
 	"golang.org/x/tools/go/gcexportdata"
 )
 
-// A LoadMode specifies the amount of detail to return when loading.
+// A LoadMode controls the amount of detail to return when loading.
-// Higher-numbered modes cause Load to return more information,
+// The bits below can be combined to specify which fields should be
-// but may be slower. Load may return more information than requested.
+// filled in the result packages.
+// The zero value is a special case, equivalent to combining
+// the NeedName, NeedFiles, and NeedCompiledGoFiles bits.
+// ID and Errors (if present) will always be filled.
+// Load may return more information than requested.
 type LoadMode int
 
 const (
-	// The following constants are used to specify which fields of the Package
-	// should be filled when loading is done. As a special case to provide
-	// backwards compatibility, a LoadMode of 0 is equivalent to LoadFiles.
-	// For all other LoadModes, the bits below specify which fields will be filled
-	// in the result packages.
-	// WARNING: This part of the go/packages API is EXPERIMENTAL. It might
-	// be changed or removed up until April 15 2019. After that date it will
-	// be frozen.
-	// TODO(matloob): Remove this comment on April 15.
-
-	// ID and Errors (if present) will always be filled.
-
 	// NeedName adds Name and PkgPath.
 	NeedName LoadMode = 1 << iota
 
@@ -56,8 +48,8 @@ const (
 	// "placeholder" Packages with only the ID set.
 	NeedImports
 
-	// NeedDeps adds the fields requested by the LoadMode in the packages in Imports. If NeedImports
+	// NeedDeps adds the fields requested by the LoadMode in the packages in Imports.
-	// is not set NeedDeps has no effect.
+	// If NeedImports is not set, it will be added automatically.
 	NeedDeps
 
 	// NeedExportsFile adds ExportsFile.
@@ -69,7 +61,7 @@ const (
 	// NeedSyntax adds Syntax.
 	NeedSyntax
 
-	// NeedTypesInfo adds TypesInfo.
+	// NeedTypesInfo adds TypesInfo. If NeedImports is not set, it will be added automatically.
 	NeedTypesInfo
 
 	// NeedTypesSizes adds TypesSizes.
@@ -77,31 +69,25 @@ const (
 )
 
 const (
-	// LoadFiles finds the packages and computes their source file lists.
+	// Deprecated: LoadFiles exists for historical compatibility
-	// Package fields: ID, Name, Errors, GoFiles, CompiledGoFiles, and OtherFiles.
+	// and should not be used. Please directly specify the needed fields using the Need values.
 	LoadFiles = NeedName | NeedFiles | NeedCompiledGoFiles
 
-	// LoadImports adds import information for each package
+	// Deprecated: LoadImports exists for historical compatibility
-	// and its dependencies.
+	// and should not be used. Please directly specify the needed fields using the Need values.
-	// Package fields added: Imports.
+	LoadImports = LoadFiles | NeedImports
-	LoadImports = LoadFiles | NeedImports | NeedDeps
 
-	// LoadTypes adds type information for package-level
+	// Deprecated: LoadTypes exists for historical compatibility
-	// declarations in the packages matching the patterns.
+	// and should not be used. Please directly specify the needed fields using the Need values.
-	// Package fields added: Types, TypesSizes, Fset, and IllTyped.
-	// This mode uses type information provided by the build system when
-	// possible, and may fill in the ExportFile field.
 	LoadTypes = LoadImports | NeedTypes | NeedTypesSizes
 
-	// LoadSyntax adds typed syntax trees for the packages matching the patterns.
+	// Deprecated: LoadSyntax exists for historical compatibility
-	// Package fields added: Syntax, and TypesInfo, for direct pattern matches only.
+	// and should not be used. Please directly specify the needed fields using the Need values.
 	LoadSyntax = LoadTypes | NeedSyntax | NeedTypesInfo
 
-	// LoadAllSyntax adds typed syntax trees for the packages matching the patterns
+	// Deprecated: LoadAllSyntax exists for historical compatibility
-	// and all dependencies.
+	// and should not be used. Please directly specify the needed fields using the Need values.
-	// Package fields added: Types, Fset, IllTyped, Syntax, and TypesInfo,
+	LoadAllSyntax = LoadSyntax | NeedDeps
-	// for all packages in the import graph.
-	LoadAllSyntax = LoadSyntax
 )
 
 // A Config specifies details about how packages should be loaded.
@@ -117,6 +103,12 @@ type Config struct {
 	// If Context is nil, the load cannot be cancelled.
 	Context context.Context
 
+	// Logf is the logger for the config.
+	// If the user provides a logger, debug logging is enabled.
+	// If the GOPACKAGESDEBUG environment variable is set to true,
+	// but the logger is nil, default to log.Printf.
+	Logf func(format string, args ...interface{})
+
 	// Dir is the directory in which to run the build system's query tool
 	// that provides information about the packages.
 	// If Dir is empty, the tool is run in the current directory.
@@ -275,9 +267,9 @@ type Package struct {
 	Imports map[string]*Package
 
 	// Types provides type information for the package.
-	// Modes LoadTypes and above set this field for packages matching the
+	// The NeedTypes LoadMode bit sets this field for packages matching the
-	// patterns; type information for dependencies may be missing or incomplete.
+	// patterns; type information for dependencies may be missing or incomplete,
-	// Mode LoadAllSyntax sets this field for all packages, including dependencies.
+	// unless NeedDeps and NeedImports are also set.
 	Types *types.Package
 
 	// Fset provides position information for Types, TypesInfo, and Syntax.
@@ -290,8 +282,9 @@ type Package struct {
 
 	// Syntax is the package's syntax trees, for the files listed in CompiledGoFiles.
 	//
-	// Mode LoadSyntax sets this field for packages matching the patterns.
+	// The NeedSyntax LoadMode bit populates this field for packages matching the patterns.
-	// Mode LoadAllSyntax sets this field for all packages, including dependencies.
+	// If NeedDeps and NeedImports are also set, this field will also be populated
+	// for dependencies.
 	Syntax []*ast.File
 
 	// TypesInfo provides type information about the package's syntax trees.
@@ -442,9 +435,20 @@ func newLoader(cfg *Config) *loader {
 	}
 	if cfg != nil {
 		ld.Config = *cfg
+		// If the user has provided a logger, use it.
+		ld.Config.Logf = cfg.Logf
+	}
+	if ld.Config.Logf == nil {
+		// If the GOPACKAGESDEBUG environment variable is set to true,
+		// but the user has not provided a logger, default to log.Printf.
+		if debug {
+			ld.Config.Logf = log.Printf
+		} else {
+			ld.Config.Logf = func(format string, args ...interface{}) {}
+		}
 	}
 	if ld.Config.Mode == 0 {
-		ld.Config.Mode = LoadFiles // Preserve zero behavior of Mode for backwards compatibility.
+		ld.Config.Mode = NeedName | NeedFiles | NeedCompiledGoFiles // Preserve zero behavior of Mode for backwards compatibility.
 	}
 	if ld.Config.Env == nil {
 		ld.Config.Env = os.Environ()
@@ -472,6 +476,8 @@ func newLoader(cfg *Config) *loader {
 			}
 		}
 	}
+
+	ld.addDependingLoadModes()
 	return ld
 }
 
@@ -492,8 +498,8 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 		}
 		lpkg := &loaderPackage{
 			Package:   pkg,
-			needtypes: (ld.Mode&(NeedTypes|NeedTypesInfo) != 0 && rootIndex < 0) || rootIndex >= 0,
+			needtypes: (ld.Mode&(NeedTypes|NeedTypesInfo) != 0 && ld.Mode&NeedDeps != 0 && rootIndex < 0) || rootIndex >= 0,
-			needsrc: (ld.Mode&(NeedSyntax|NeedTypesInfo) != 0 && rootIndex < 0) || rootIndex >= 0 ||
+			needsrc: (ld.Mode&(NeedSyntax|NeedTypesInfo) != 0 && ld.Mode&NeedDeps != 0 && rootIndex < 0) || rootIndex >= 0 ||
 				len(ld.Overlay) > 0 || // Overlays can invalidate export data. TODO(matloob): make this check fine-grained based on dependencies on overlaid files
 				pkg.ExportFile == "" && pkg.PkgPath != "unsafe",
 		}
@@ -540,28 +546,31 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 		lpkg.color = grey
 		stack = append(stack, lpkg) // push
 		stubs := lpkg.Imports       // the structure form has only stubs with the ID in the Imports
-		lpkg.Imports = make(map[string]*Package, len(stubs))
+		// If NeedImports isn't set, the imports fields will all be zeroed out.
-		for importPath, ipkg := range stubs {
+		if ld.Mode&NeedImports != 0 {
-			var importErr error
+			lpkg.Imports = make(map[string]*Package, len(stubs))
-			imp := ld.pkgs[ipkg.ID]
+			for importPath, ipkg := range stubs {
-			if imp == nil {
+				var importErr error
-				// (includes package "C" when DisableCgo)
+				imp := ld.pkgs[ipkg.ID]
-				importErr = fmt.Errorf("missing package: %q", ipkg.ID)
+				if imp == nil {
-			} else if imp.color == grey {
+					// (includes package "C" when DisableCgo)
-				importErr = fmt.Errorf("import cycle: %s", stack)
+					importErr = fmt.Errorf("missing package: %q", ipkg.ID)
-			}
+				} else if imp.color == grey {
-			if importErr != nil {
+					importErr = fmt.Errorf("import cycle: %s", stack)
-				if lpkg.importErrors == nil {
+				}
-					lpkg.importErrors = make(map[string]error)
+				if importErr != nil {
+					if lpkg.importErrors == nil {
+						lpkg.importErrors = make(map[string]error)
+					}
+					lpkg.importErrors[importPath] = importErr
+					continue
 				}
-				lpkg.importErrors[importPath] = importErr
-				continue
-			}
 
-			if visit(imp) {
+				if visit(imp) {
-				lpkg.needsrc = true
+					lpkg.needsrc = true
+				}
+				lpkg.Imports[importPath] = imp.Package
 			}
-			lpkg.Imports[importPath] = imp.Package
 		}
 		if lpkg.needsrc {
 			srcPkgs = append(srcPkgs, lpkg)
@@ -575,7 +584,7 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 		return lpkg.needsrc
 	}
 
-	if ld.Mode&(NeedImports|NeedDeps) == 0 {
+	if ld.Mode&NeedImports == 0 {
 		// We do this to drop the stub import packages that we are not even going to try to resolve.
 		for _, lpkg := range initial {
 			lpkg.Imports = nil
@@ -586,7 +595,7 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 			visit(lpkg)
 		}
 	}
-	if ld.Mode&NeedDeps != 0 { // TODO(matloob): This is only the case if NeedTypes is also set, right?
+	if ld.Mode&NeedImports != 0 && ld.Mode&NeedTypes != 0 {
 		for _, lpkg := range srcPkgs {
 			// Complete type information is required for the
 			// immediate dependencies of each source package.
@@ -611,7 +620,6 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 	}
 
 	result := make([]*Package, len(initial))
-	importPlaceholders := make(map[string]*Package)
 	for i, lpkg := range initial {
 		result[i] = lpkg.Package
 	}
@@ -648,17 +656,8 @@ func (ld *loader) refine(roots []string, list ...*Package) ([]*Package, error) {
 		if ld.Mode&NeedTypesSizes == 0 {
 			ld.pkgs[i].TypesSizes = nil
 		}
-		if ld.Mode&NeedDeps == 0 {
-			for j, pkg := range ld.pkgs[i].Imports {
-				ph, ok := importPlaceholders[pkg.ID]
-				if !ok {
-					ph = &Package{ID: pkg.ID}
-					importPlaceholders[pkg.ID] = ph
-				}
-				ld.pkgs[i].Imports[j] = ph
-			}
-		}
 	}
+
 	return result, nil
 }
 
@@ -679,7 +678,6 @@ func (ld *loader) loadRecursive(lpkg *loaderPackage) {
 			}(imp)
 		}
 		wg.Wait()
-
 		ld.loadPackage(lpkg)
 	})
 }
@@ -687,7 +685,7 @@ func (ld *loader) loadRecursive(lpkg *loaderPackage) {
 // loadPackage loads the specified package.
 // It must be called only once per Package,
 // after immediate dependencies are loaded.
-// Precondition: ld.Mode >= LoadTypes.
+// Precondition: ld.Mode & NeedTypes.
 func (ld *loader) loadPackage(lpkg *loaderPackage) {
 	if lpkg.PkgPath == "unsafe" {
 		// Fill in the blanks to avoid surprises.
@@ -806,7 +804,7 @@ func (ld *loader) loadPackage(lpkg *loaderPackage) {
 		if ipkg.Types != nil && ipkg.Types.Complete() {
 			return ipkg.Types, nil
 		}
-		log.Fatalf("internal error: nil Pkg importing %q from %q", path, lpkg)
+		log.Fatalf("internal error: package %q without types was imported from %q", path, lpkg)
 		panic("unreachable")
 	})
 
@@ -817,7 +815,7 @@ func (ld *loader) loadPackage(lpkg *loaderPackage) {
 		// Type-check bodies of functions only in non-initial packages.
 		// Example: for import graph A->B->C and initial packages {A,C},
 		// we can ignore function bodies in B.
-		IgnoreFuncBodies: (ld.Mode&(NeedDeps|NeedTypesInfo) == 0) && !lpkg.initial,
+		IgnoreFuncBodies: ld.Mode&NeedDeps == 0 && !lpkg.initial,
 
 		Error: appendError,
 		Sizes: ld.sizes,
@@ -1079,6 +1077,25 @@ func (ld *loader) loadFromExportData(lpkg *loaderPackage) (*types.Package, error
 	return tpkg, nil
 }
 
-func usesExportData(cfg *Config) bool {
+// addDependingLoadModes adds dependencies for choosed LoadMode in ld.Mode
-	return cfg.Mode&NeedExportsFile != 0 || cfg.Mode&NeedTypes != 0 && cfg.Mode&NeedTypesInfo == 0
+func (ld *loader) addDependingLoadModes() {
+	if ld.Mode&NeedTypesInfo != 0 && ld.Mode&NeedImports == 0 {
+		// If NeedTypesInfo, go/packages needs to do typechecking itself so it can
+		// associate type info with the AST. To do so, we need the export data
+		// for dependencies, which means we need to ask for the direct dependencies.
+		// NeedImports is used to ask for the direct dependencies.
+		ld.Mode |= NeedImports
+		ld.Logf("Added load mode dependency of NeedTypesInfo: NeedImports")
+	}
+
+	if ld.Mode&NeedDeps != 0 && ld.Mode&NeedImports == 0 {
+		// With NeedDeps we need to load at least direct dependencies.
+		// NeedImports is used to ask for the direct dependencies.
+		ld.Mode |= NeedImports
+		ld.Logf("Added load mode dependency of NeedDeps: NeedImports")
+	}
+}
+
+func usesExportData(cfg *Config) bool {
+	return cfg.Mode&NeedExportsFile != 0 || cfg.Mode&NeedTypes != 0 && cfg.Mode&NeedDeps == 0
 }

vendor/golang.org/x/tools/go/ssa/ssautil/load.go

@@ -101,7 +101,7 @@ func doPackages(initial []*packages.Package, mode ssa.BuilderMode, deps bool) (*
 //
 // The mode parameter controls diagnostics and checking during SSA construction.
 //
-// Deprecated: use golang.org/x/tools/go/packages and the Packages
+// Deprecated: Use golang.org/x/tools/go/packages and the Packages
 // function instead; see ssa.ExampleLoadPackages.
 //
 func CreateProgram(lprog *loader.Program, mode ssa.BuilderMode) *ssa.Program {

vendor/golang.org/x/tools/go/ssa/testmain.go

@@ -27,7 +27,8 @@ import (
 // (as defined by "go test") defined in the specified package,
 // and its TestMain function, if any.
 //
-// Deprecated: use x/tools/go/packages to access synthetic testmain packages.
+// Deprecated: Use golang.org/x/tools/go/packages to access synthetic
+// testmain packages.
 func FindTests(pkg *Package) (tests, benchmarks, examples []*Function, main *Function) {
 	prog := pkg.Prog
 
@@ -112,7 +113,8 @@ func isTest(name, prefix string) bool {
 // Subsequent calls to prog.AllPackages include the new package.
 // The package pkg must belong to the program prog.
 //
-// Deprecated: use x/tools/go/packages to access synthetic testmain packages.
+// Deprecated: Use golang.org/x/tools/go/packages to access synthetic
+// testmain packages.
 func (prog *Program) CreateTestMainPackage(pkg *Package) *Package {
 	if pkg.Prog != prog {
 		log.Fatal("Package does not belong to Program")

vendor/golang.org/x/tools/internal/gopathwalk/walk.go

@@ -59,15 +59,27 @@ func SrcDirsRoots(ctx *build.Context) []Root {
 // paths of the containing source directory and the package directory.
 // add will be called concurrently.
 func Walk(roots []Root, add func(root Root, dir string), opts Options) {
+	WalkSkip(roots, add, func(Root, string) bool { return false }, opts)
+}
+
+// WalkSkip walks Go source directories ($GOROOT, $GOPATH, etc) to find packages.
+// For each package found, add will be called (concurrently) with the absolute
+// paths of the containing source directory and the package directory.
+// For each directory that will be scanned, skip will be called (concurrently)
+// with the absolute paths of the containing source directory and the directory.
+// If skip returns false on a directory it will be processed.
+// add will be called concurrently.
+// skip will be called concurrently.
+func WalkSkip(roots []Root, add func(root Root, dir string), skip func(root Root, dir string) bool, opts Options) {
 	for _, root := range roots {
-		walkDir(root, add, opts)
+		walkDir(root, add, skip, opts)
 	}
 }
 
-func walkDir(root Root, add func(Root, string), opts Options) {
+func walkDir(root Root, add func(Root, string), skip func(root Root, dir string) bool, opts Options) {
 	if _, err := os.Stat(root.Path); os.IsNotExist(err) {
 		if opts.Debug {
-			log.Printf("skipping nonexistant directory: %v", root.Path)
+			log.Printf("skipping nonexistent directory: %v", root.Path)
 		}
 		return
 	}
@@ -77,6 +89,7 @@ func walkDir(root Root, add func(Root, string), opts Options) {
 	w := &walker{
 		root: root,
 		add:  add,
+		skip: skip,
 		opts: opts,
 	}
 	w.init()
@@ -91,9 +104,10 @@ func walkDir(root Root, add func(Root, string), opts Options) {
 
 // walker is the callback for fastwalk.Walk.
 type walker struct {
-	root Root               // The source directory to scan.
+	root Root                    // The source directory to scan.
-	add  func(Root, string) // The callback that will be invoked for every possible Go package dir.
+	add  func(Root, string)      // The callback that will be invoked for every possible Go package dir.
-	opts Options            // Options passed to Walk by the user.
+	skip func(Root, string) bool // The callback that will be invoked for every dir. dir is skipped if it returns true.
+	opts Options                 // Options passed to Walk by the user.
 
 	ignoredDirs []os.FileInfo // The ignored directories, loaded from .goimportsignore files.
 }
@@ -151,12 +165,16 @@ func (w *walker) getIgnoredDirs(path string) []string {
 	return ignoredDirs
 }
 
-func (w *walker) shouldSkipDir(fi os.FileInfo) bool {
+func (w *walker) shouldSkipDir(fi os.FileInfo, dir string) bool {
 	for _, ignoredDir := range w.ignoredDirs {
 		if os.SameFile(fi, ignoredDir) {
 			return true
 		}
 	}
+	if w.skip != nil {
+		// Check with the user specified callback.
+		return w.skip(w.root, dir)
+	}
 	return false
 }
 
@@ -184,7 +202,7 @@ func (w *walker) walk(path string, typ os.FileMode) error {
 			return filepath.SkipDir
 		}
 		fi, err := os.Lstat(path)
-		if err == nil && w.shouldSkipDir(fi) {
+		if err == nil && w.shouldSkipDir(fi, path) {
 			return filepath.SkipDir
 		}
 		return nil
@@ -224,7 +242,7 @@ func (w *walker) shouldTraverse(dir string, fi os.FileInfo) bool {
 	if !ts.IsDir() {
 		return false
 	}
-	if w.shouldSkipDir(ts) {
+	if w.shouldSkipDir(ts, dir) {
 		return false
 	}
 	// Check for symlink loops by statting each directory component

vendor/golang.org/x/tools/internal/imports/fix.go

@@ -13,7 +13,6 @@ import (
 	"go/parser"
 	"go/token"
 	"io/ioutil"
-	"log"
 	"os"
 	"os/exec"
 	"path"
@@ -68,10 +67,27 @@ func importGroup(env *ProcessEnv, importPath string) int {
 	return 0
 }
 
-// An importInfo represents a single import statement.
+type ImportFixType int
-type importInfo struct {
+
-	importPath string // import path, e.g. "crypto/rand".
+const (
-	name       string // import name, e.g. "crand", or "" if none.
+	AddImport ImportFixType = iota
+	DeleteImport
+	SetImportName
+)
+
+type ImportFix struct {
+	// StmtInfo represents the import statement this fix will add, remove, or change.
+	StmtInfo ImportInfo
+	// IdentName is the identifier that this fix will add or remove.
+	IdentName string
+	// FixType is the type of fix this is (AddImport, DeleteImport, SetImportName).
+	FixType ImportFixType
+}
+
+// An ImportInfo represents a single import statement.
+type ImportInfo struct {
+	ImportPath string // import path, e.g. "crypto/rand".
+	Name       string // import name, e.g. "crand", or "" if none.
 }
 
 // A packageInfo represents what's known about a package.
@@ -169,10 +185,10 @@ func collectReferences(f *ast.File) references {
 	return refs
 }
 
-// collectImports returns all the imports in f, keyed by their package name as
+// collectImports returns all the imports in f.
-// determined by pathToName. Unnamed imports (., _) and "C" are ignored.
+// Unnamed imports (., _) and "C" are ignored.
-func collectImports(f *ast.File) []*importInfo {
+func collectImports(f *ast.File) []*ImportInfo {
-	var imports []*importInfo
+	var imports []*ImportInfo
 	for _, imp := range f.Imports {
 		var name string
 		if imp.Name != nil {
@@ -182,9 +198,9 @@ func collectImports(f *ast.File) []*importInfo {
 			continue
 		}
 		path := strings.Trim(imp.Path.Value, `"`)
-		imports = append(imports, &importInfo{
+		imports = append(imports, &ImportInfo{
-			name:       name,
+			Name:       name,
-			importPath: path,
+			ImportPath: path,
 		})
 	}
 	return imports
@@ -192,9 +208,9 @@ func collectImports(f *ast.File) []*importInfo {
 
 // findMissingImport searches pass's candidates for an import that provides
 // pkg, containing all of syms.
-func (p *pass) findMissingImport(pkg string, syms map[string]bool) *importInfo {
+func (p *pass) findMissingImport(pkg string, syms map[string]bool) *ImportInfo {
 	for _, candidate := range p.candidates {
-		pkgInfo, ok := p.knownPackages[candidate.importPath]
+		pkgInfo, ok := p.knownPackages[candidate.ImportPath]
 		if !ok {
 			continue
 		}
@@ -234,27 +250,33 @@ type pass struct {
 	otherFiles           []*ast.File    // sibling files.
 
 	// Intermediate state, generated by load.
-	existingImports map[string]*importInfo
+	existingImports map[string]*ImportInfo
 	allRefs         references
 	missingRefs     references
 
 	// Inputs to fix. These can be augmented between successive fix calls.
 	lastTry       bool                    // indicates that this is the last call and fix should clean up as best it can.
-	candidates    []*importInfo           // candidate imports in priority order.
+	candidates    []*ImportInfo           // candidate imports in priority order.
 	knownPackages map[string]*packageInfo // information about all known packages.
 }
 
 // loadPackageNames saves the package names for everything referenced by imports.
-func (p *pass) loadPackageNames(imports []*importInfo) error {
+func (p *pass) loadPackageNames(imports []*ImportInfo) error {
+	if p.env.Debug {
+		p.env.Logf("loading package names for %v packages", len(imports))
+		defer func() {
+			p.env.Logf("done loading package names for %v packages", len(imports))
+		}()
+	}
 	var unknown []string
 	for _, imp := range imports {
-		if _, ok := p.knownPackages[imp.importPath]; ok {
+		if _, ok := p.knownPackages[imp.ImportPath]; ok {
 			continue
 		}
-		unknown = append(unknown, imp.importPath)
+		unknown = append(unknown, imp.ImportPath)
 	}
 
-	names, err := p.env.getResolver().loadPackageNames(unknown, p.srcDir)
+	names, err := p.env.GetResolver().loadPackageNames(unknown, p.srcDir)
 	if err != nil {
 		return err
 	}
@@ -271,24 +293,24 @@ func (p *pass) loadPackageNames(imports []*importInfo) error {
 // importIdentifier returns the identifier that imp will introduce. It will
 // guess if the package name has not been loaded, e.g. because the source
 // is not available.
-func (p *pass) importIdentifier(imp *importInfo) string {
+func (p *pass) importIdentifier(imp *ImportInfo) string {
-	if imp.name != "" {
+	if imp.Name != "" {
-		return imp.name
+		return imp.Name
 	}
-	known := p.knownPackages[imp.importPath]
+	known := p.knownPackages[imp.ImportPath]
 	if known != nil && known.name != "" {
 		return known.name
 	}
-	return importPathToAssumedName(imp.importPath)
+	return importPathToAssumedName(imp.ImportPath)
 }
 
 // load reads in everything necessary to run a pass, and reports whether the
 // file already has all the imports it needs. It fills in p.missingRefs with the
 // file's missing symbols, if any, or removes unused imports if not.
-func (p *pass) load() bool {
+func (p *pass) load() ([]*ImportFix, bool) {
 	p.knownPackages = map[string]*packageInfo{}
 	p.missingRefs = references{}
-	p.existingImports = map[string]*importInfo{}
+	p.existingImports = map[string]*ImportInfo{}
 
 	// Load basic information about the file in question.
 	p.allRefs = collectReferences(p.f)
@@ -313,9 +335,9 @@ func (p *pass) load() bool {
 		err := p.loadPackageNames(append(imports, p.candidates...))
 		if err != nil {
 			if p.env.Debug {
-				log.Printf("loading package names: %v", err)
+				p.env.Logf("loading package names: %v", err)
 			}
-			return false
+			return nil, false
 		}
 	}
 	for _, imp := range imports {
@@ -334,18 +356,18 @@ func (p *pass) load() bool {
 		}
 	}
 	if len(p.missingRefs) != 0 {
-		return false
+		return nil, false
 	}
 
 	return p.fix()
 }
 
 // fix attempts to satisfy missing imports using p.candidates. If it finds
-// everything, or if p.lastTry is true, it adds the imports it found,
+// everything, or if p.lastTry is true, it updates fixes to add the imports it found,
-// removes anything unused, and returns true.
+// delete anything unused, and update import names, and returns true.
-func (p *pass) fix() bool {
+func (p *pass) fix() ([]*ImportFix, bool) {
 	// Find missing imports.
-	var selected []*importInfo
+	var selected []*ImportInfo
 	for left, rights := range p.missingRefs {
 		if imp := p.findMissingImport(left, rights); imp != nil {
 			selected = append(selected, imp)
@@ -353,10 +375,11 @@ func (p *pass) fix() bool {
 	}
 
 	if !p.lastTry && len(selected) != len(p.missingRefs) {
-		return false
+		return nil, false
 	}
 
 	// Found everything, or giving up. Add the new imports and remove any unused.
+	var fixes []*ImportFix
 	for _, imp := range p.existingImports {
 		// We deliberately ignore globals here, because we can't be sure
 		// they're in the same package. People do things like put multiple
@@ -364,28 +387,80 @@ func (p *pass) fix() bool {
 		// remove imports if they happen to have the same name as a var in
 		// a different package.
 		if _, ok := p.allRefs[p.importIdentifier(imp)]; !ok {
-			astutil.DeleteNamedImport(p.fset, p.f, imp.name, imp.importPath)
+			fixes = append(fixes, &ImportFix{
+				StmtInfo:  *imp,
+				IdentName: p.importIdentifier(imp),
+				FixType:   DeleteImport,
+			})
+			continue
+		}
+
+		// An existing import may need to update its import name to be correct.
+		if name := p.importSpecName(imp); name != imp.Name {
+			fixes = append(fixes, &ImportFix{
+				StmtInfo: ImportInfo{
+					Name:       name,
+					ImportPath: imp.ImportPath,
+				},
+				IdentName: p.importIdentifier(imp),
+				FixType:   SetImportName,
+			})
 		}
 	}
 
 	for _, imp := range selected {
-		astutil.AddNamedImport(p.fset, p.f, imp.name, imp.importPath)
+		fixes = append(fixes, &ImportFix{
+			StmtInfo: ImportInfo{
+				Name:       p.importSpecName(imp),
+				ImportPath: imp.ImportPath,
+			},
+			IdentName: p.importIdentifier(imp),
+			FixType:   AddImport,
+		})
 	}
 
-	if p.loadRealPackageNames {
+	return fixes, true
-		for _, imp := range p.f.Imports {
+}
-			if imp.Name != nil {
+
-				continue
+// importSpecName gets the import name of imp in the import spec.
-			}
+//
-			path := strings.Trim(imp.Path.Value, `""`)
+// When the import identifier matches the assumed import name, the import name does
-			ident := p.importIdentifier(&importInfo{importPath: path})
+// not appear in the import spec.
-			if ident != importPathToAssumedName(path) {
+func (p *pass) importSpecName(imp *ImportInfo) string {
-				imp.Name = &ast.Ident{Name: ident, NamePos: imp.Pos()}
+	// If we did not load the real package names, or the name is already set,
+	// we just return the existing name.
+	if !p.loadRealPackageNames || imp.Name != "" {
+		return imp.Name
+	}
+
+	ident := p.importIdentifier(imp)
+	if ident == importPathToAssumedName(imp.ImportPath) {
+		return "" // ident not needed since the assumed and real names are the same.
+	}
+	return ident
+}
+
+// apply will perform the fixes on f in order.
+func apply(fset *token.FileSet, f *ast.File, fixes []*ImportFix) {
+	for _, fix := range fixes {
+		switch fix.FixType {
+		case DeleteImport:
+			astutil.DeleteNamedImport(fset, f, fix.StmtInfo.Name, fix.StmtInfo.ImportPath)
+		case AddImport:
+			astutil.AddNamedImport(fset, f, fix.StmtInfo.Name, fix.StmtInfo.ImportPath)
+		case SetImportName:
+			// Find the matching import path and change the name.
+			for _, spec := range f.Imports {
+				path := strings.Trim(spec.Path.Value, `"`)
+				if path == fix.StmtInfo.ImportPath {
+					spec.Name = &ast.Ident{
+						Name:    fix.StmtInfo.Name,
+						NamePos: spec.Pos(),
+					}
+				}
 			}
 		}
 	}
-
-	return true
 }
 
 // assumeSiblingImportsValid assumes that siblings' use of packages is valid,
@@ -394,15 +469,15 @@ func (p *pass) assumeSiblingImportsValid() {
 	for _, f := range p.otherFiles {
 		refs := collectReferences(f)
 		imports := collectImports(f)
-		importsByName := map[string]*importInfo{}
+		importsByName := map[string]*ImportInfo{}
 		for _, imp := range imports {
 			importsByName[p.importIdentifier(imp)] = imp
 		}
 		for left, rights := range refs {
 			if imp, ok := importsByName[left]; ok {
-				if _, ok := stdlib[imp.importPath]; ok {
+				if _, ok := stdlib[imp.ImportPath]; ok {
 					// We have the stdlib in memory; no need to guess.
-					rights = stdlib[imp.importPath]
+					rights = stdlib[imp.ImportPath]
 				}
 				p.addCandidate(imp, &packageInfo{
 					// no name; we already know it.
@@ -415,9 +490,9 @@ func (p *pass) assumeSiblingImportsValid() {
 
 // addCandidate adds a candidate import to p, and merges in the information
 // in pkg.
-func (p *pass) addCandidate(imp *importInfo, pkg *packageInfo) {
+func (p *pass) addCandidate(imp *ImportInfo, pkg *packageInfo) {
 	p.candidates = append(p.candidates, imp)
-	if existing, ok := p.knownPackages[imp.importPath]; ok {
+	if existing, ok := p.knownPackages[imp.ImportPath]; ok {
 		if existing.name == "" {
 			existing.name = pkg.name
 		}
@@ -425,7 +500,7 @@ func (p *pass) addCandidate(imp *importInfo, pkg *packageInfo) {
 			existing.exports[export] = true
 		}
 	} else {
-		p.knownPackages[imp.importPath] = pkg
+		p.knownPackages[imp.ImportPath] = pkg
 	}
 }
 
@@ -437,13 +512,24 @@ func (p *pass) addCandidate(imp *importInfo, pkg *packageInfo) {
 var fixImports = fixImportsDefault
 
 func fixImportsDefault(fset *token.FileSet, f *ast.File, filename string, env *ProcessEnv) error {
-	abs, err := filepath.Abs(filename)
+	fixes, err := getFixes(fset, f, filename, env)
 	if err != nil {
 		return err
 	}
+	apply(fset, f, fixes)
+	return err
+}
+
+// getFixes gets the import fixes that need to be made to f in order to fix the imports.
+// It does not modify the ast.
+func getFixes(fset *token.FileSet, f *ast.File, filename string, env *ProcessEnv) ([]*ImportFix, error) {
+	abs, err := filepath.Abs(filename)
+	if err != nil {
+		return nil, err
+	}
 	srcDir := filepath.Dir(abs)
 	if env.Debug {
-		log.Printf("fixImports(filename=%q), abs=%q, srcDir=%q ...", filename, abs, srcDir)
+		env.Logf("fixImports(filename=%q), abs=%q, srcDir=%q ...", filename, abs, srcDir)
 	}
 
 	// First pass: looking only at f, and using the naive algorithm to
@@ -451,8 +537,8 @@ func fixImportsDefault(fset *token.FileSet, f *ast.File, filename string, env *P
 	// complete. We can't add any imports yet, because we don't know
 	// if missing references are actually package vars.
 	p := &pass{fset: fset, f: f, srcDir: srcDir}
-	if p.load() {
+	if fixes, done := p.load(); done {
-		return nil
+		return fixes, nil
 	}
 
 	otherFiles := parseOtherFiles(fset, srcDir, filename)
@@ -460,15 +546,15 @@ func fixImportsDefault(fset *token.FileSet, f *ast.File, filename string, env *P
 	// Second pass: add information from other files in the same package,
 	// like their package vars and imports.
 	p.otherFiles = otherFiles
-	if p.load() {
+	if fixes, done := p.load(); done {
-		return nil
+		return fixes, nil
 	}
 
 	// Now we can try adding imports from the stdlib.
 	p.assumeSiblingImportsValid()
 	addStdlibCandidates(p, p.missingRefs)
-	if p.fix() {
+	if fixes, done := p.fix(); done {
-		return nil
+		return fixes, nil
 	}
 
 	// Third pass: get real package names where we had previously used
@@ -477,25 +563,50 @@ func fixImportsDefault(fset *token.FileSet, f *ast.File, filename string, env *P
 	p = &pass{fset: fset, f: f, srcDir: srcDir, env: env}
 	p.loadRealPackageNames = true
 	p.otherFiles = otherFiles
-	if p.load() {
+	if fixes, done := p.load(); done {
-		return nil
+		return fixes, nil
 	}
 
 	addStdlibCandidates(p, p.missingRefs)
 	p.assumeSiblingImportsValid()
-	if p.fix() {
+	if fixes, done := p.fix(); done {
-		return nil
+		return fixes, nil
 	}
 
 	// Go look for candidates in $GOPATH, etc. We don't necessarily load
 	// the real exports of sibling imports, so keep assuming their contents.
 	if err := addExternalCandidates(p, p.missingRefs, filename); err != nil {
-		return err
+		return nil, err
 	}
 
 	p.lastTry = true
-	p.fix()
+	fixes, _ := p.fix()
-	return nil
+	return fixes, nil
+}
+
+// getAllCandidates gets all of the candidates to be imported, regardless of if they are needed.
+func getAllCandidates(filename string, env *ProcessEnv) ([]ImportFix, error) {
+	// TODO(suzmue): scan for additional candidates and filter out
+	// current package.
+
+	// Get the stdlib candidates and sort by import path.
+	var paths []string
+	for importPath := range stdlib {
+		paths = append(paths, importPath)
+	}
+	sort.Strings(paths)
+
+	var imports []ImportFix
+	for _, importPath := range paths {
+		imports = append(imports, ImportFix{
+			StmtInfo: ImportInfo{
+				ImportPath: importPath,
+			},
+			IdentName: path.Base(importPath),
+			FixType:   AddImport,
+		})
+	}
+	return imports, nil
 }
 
 // ProcessEnv contains environment variables and settings that affect the use of
@@ -506,13 +617,16 @@ type ProcessEnv struct {
 
 	// If non-empty, these will be used instead of the
 	// process-wide values.
-	GOPATH, GOROOT, GO111MODULE, GOPROXY, GOFLAGS string
+	GOPATH, GOROOT, GO111MODULE, GOPROXY, GOFLAGS, GOSUMDB string
-	WorkingDir                                    string
+	WorkingDir                                             string
 
 	// If true, use go/packages regardless of the environment.
 	ForceGoPackages bool
 
-	resolver resolver
+	// Logf is the default logger for the ProcessEnv.
+	Logf func(format string, args ...interface{})
+
+	resolver Resolver
 }
 
 func (e *ProcessEnv) env() []string {
@@ -527,25 +641,29 @@ func (e *ProcessEnv) env() []string {
 	add("GO111MODULE", e.GO111MODULE)
 	add("GOPROXY", e.GOPROXY)
 	add("GOFLAGS", e.GOFLAGS)
+	add("GOSUMDB", e.GOSUMDB)
 	if e.WorkingDir != "" {
 		add("PWD", e.WorkingDir)
 	}
 	return env
 }
 
-func (e *ProcessEnv) getResolver() resolver {
+func (e *ProcessEnv) GetResolver() Resolver {
 	if e.resolver != nil {
 		return e.resolver
 	}
 	if e.ForceGoPackages {
-		return &goPackagesResolver{env: e}
+		e.resolver = &goPackagesResolver{env: e}
+		return e.resolver
 	}
 
 	out, err := e.invokeGo("env", "GOMOD")
 	if err != nil || len(bytes.TrimSpace(out.Bytes())) == 0 {
-		return &gopathResolver{env: e}
+		e.resolver = &gopathResolver{env: e}
+		return e.resolver
 	}
-	return &moduleResolver{env: e}
+	e.resolver = &ModuleResolver{env: e}
+	return e.resolver
 }
 
 func (e *ProcessEnv) newPackagesConfig(mode packages.LoadMode) *packages.Config {
@@ -573,7 +691,7 @@ func (e *ProcessEnv) invokeGo(args ...string) (*bytes.Buffer, error) {
 	cmd.Dir = e.WorkingDir
 
 	if e.Debug {
-		defer func(start time.Time) { log.Printf("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())
+		defer func(start time.Time) { e.Logf("%s for %v", time.Since(start), cmdDebugStr(cmd)) }(time.Now())
 	}
 	if err := cmd.Run(); err != nil {
 		return nil, fmt.Errorf("running go: %v (stderr:\n%s)", err, stderr)
@@ -595,7 +713,7 @@ func cmdDebugStr(cmd *exec.Cmd) string {
 func addStdlibCandidates(pass *pass, refs references) {
 	add := func(pkg string) {
 		pass.addCandidate(
-			&importInfo{importPath: pkg},
+			&ImportInfo{ImportPath: pkg},
 			&packageInfo{name: path.Base(pkg), exports: stdlib[pkg]})
 	}
 	for left := range refs {
@@ -613,20 +731,27 @@ func addStdlibCandidates(pass *pass, refs references) {
 	}
 }
 
-// A resolver does the build-system-specific parts of goimports.
+// A Resolver does the build-system-specific parts of goimports.
-type resolver interface {
+type Resolver interface {
 	// loadPackageNames loads the package names in importPaths.
 	loadPackageNames(importPaths []string, srcDir string) (map[string]string, error)
 	// scan finds (at least) the packages satisfying refs. The returned slice is unordered.
 	scan(refs references) ([]*pkg, error)
+	// loadExports returns the set of exported symbols in the package at dir.
+	// It returns an error if the package name in dir does not match expectPackage.
+	// loadExports may be called concurrently.
+	loadExports(ctx context.Context, expectPackage string, pkg *pkg) (map[string]bool, error)
 }
 
-// gopathResolver implements resolver for GOPATH and module workspaces using go/packages.
+// gopackagesResolver implements resolver for GOPATH and module workspaces using go/packages.
 type goPackagesResolver struct {
 	env *ProcessEnv
 }
 
 func (r *goPackagesResolver) loadPackageNames(importPaths []string, srcDir string) (map[string]string, error) {
+	if len(importPaths) == 0 {
+		return nil, nil
+	}
 	cfg := r.env.newPackagesConfig(packages.LoadFiles)
 	pkgs, err := packages.Load(cfg, importPaths...)
 	if err != nil {
@@ -670,15 +795,35 @@ func (r *goPackagesResolver) scan(refs references) ([]*pkg, error) {
 	return scan, nil
 }
 
+func (r *goPackagesResolver) loadExports(ctx context.Context, expectPackage string, pkg *pkg) (map[string]bool, error) {
+	if pkg.goPackage == nil {
+		return nil, fmt.Errorf("goPackage not set")
+	}
+	exports := map[string]bool{}
+	fset := token.NewFileSet()
+	for _, fname := range pkg.goPackage.CompiledGoFiles {
+		f, err := parser.ParseFile(fset, fname, nil, 0)
+		if err != nil {
+			return nil, fmt.Errorf("parsing %s: %v", fname, err)
+		}
+		for name := range f.Scope.Objects {
+			if ast.IsExported(name) {
+				exports[name] = true
+			}
+		}
+	}
+	return exports, nil
+}
+
 func addExternalCandidates(pass *pass, refs references, filename string) error {
-	dirScan, err := pass.env.getResolver().scan(refs)
+	dirScan, err := pass.env.GetResolver().scan(refs)
 	if err != nil {
 		return err
 	}
 
 	// Search for imports matching potential package references.
 	type result struct {
-		imp *importInfo
+		imp *ImportInfo
 		pkg *packageInfo
 	}
 	results := make(chan result, len(refs))
@@ -698,7 +843,7 @@ func addExternalCandidates(pass *pass, refs references, filename string) error {
 		go func(pkgName string, symbols map[string]bool) {
 			defer wg.Done()
 
-			found, err := findImport(ctx, pass.env, dirScan, pkgName, symbols, filename)
+			found, err := findImport(ctx, pass, dirScan, pkgName, symbols, filename)
 
 			if err != nil {
 				firstErrOnce.Do(func() {
@@ -712,8 +857,8 @@ func addExternalCandidates(pass *pass, refs references, filename string) error {
 				return // No matching package.
 			}
 
-			imp := &importInfo{
+			imp := &ImportInfo{
-				importPath: found.importPathShort,
+				ImportPath: found.importPathShort,
 			}
 
 			pkg := &packageInfo{
@@ -780,7 +925,7 @@ func (r *gopathResolver) loadPackageNames(importPaths []string, srcDir string) (
 	return names, nil
 }
 
-// importPathToNameGoPath finds out the actual package name, as declared in its .go files.
+// importPathToName finds out the actual package name, as declared in its .go files.
 // If there's a problem, it returns "".
 func importPathToName(env *ProcessEnv, importPath, srcDir string) (packageName string) {
 	// Fast path for standard library without going to disk.
@@ -800,8 +945,8 @@ func importPathToName(env *ProcessEnv, importPath, srcDir string) (packageName s
 }
 
 // packageDirToName is a faster version of build.Import if
-// the only thing desired is the package name. It uses build.FindOnly
+// the only thing desired is the package name. Given a directory,
-// to find the directory and then only parses one file in the package,
+// packageDirToName then only parses one file in the package,
 // trusting that the files in the directory are consistent.
 func packageDirToName(dir string) (packageName string, err error) {
 	d, err := os.Open(dir)
@@ -922,6 +1067,10 @@ func (r *gopathResolver) scan(_ references) ([]*pkg, error) {
 	return result, nil
 }
 
+func (r *gopathResolver) loadExports(ctx context.Context, expectPackage string, pkg *pkg) (map[string]bool, error) {
+	return loadExportsFromFiles(ctx, r.env, expectPackage, pkg.dir)
+}
+
 // VendorlessPath returns the devendorized version of the import path ipath.
 // For example, VendorlessPath("foo/bar/vendor/a/b") returns "a/b".
 func VendorlessPath(ipath string) string {
@@ -935,33 +1084,11 @@ func VendorlessPath(ipath string) string {
 	return ipath
 }
 
-// loadExports returns the set of exported symbols in the package at dir.
+func loadExportsFromFiles(ctx context.Context, env *ProcessEnv, expectPackage string, dir string) (map[string]bool, error) {
-// It returns nil on error or if the package name in dir does not match expectPackage.
-func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg *pkg) (map[string]bool, error) {
-	if env.Debug {
-		log.Printf("loading exports in dir %s (seeking package %s)", pkg.dir, expectPackage)
-	}
-	if pkg.goPackage != nil {
-		exports := map[string]bool{}
-		fset := token.NewFileSet()
-		for _, fname := range pkg.goPackage.CompiledGoFiles {
-			f, err := parser.ParseFile(fset, fname, nil, 0)
-			if err != nil {
-				return nil, fmt.Errorf("parsing %s: %v", fname, err)
-			}
-			for name := range f.Scope.Objects {
-				if ast.IsExported(name) {
-					exports[name] = true
-				}
-			}
-		}
-		return exports, nil
-	}
-
 	exports := make(map[string]bool)
 
 	// Look for non-test, buildable .go files which could provide exports.
-	all, err := ioutil.ReadDir(pkg.dir)
+	all, err := ioutil.ReadDir(dir)
 	if err != nil {
 		return nil, err
 	}
@@ -971,7 +1098,7 @@ func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg
 		if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
 			continue
 		}
-		match, err := env.buildContext().MatchFile(pkg.dir, fi.Name())
+		match, err := env.buildContext().MatchFile(dir, fi.Name())
 		if err != nil || !match {
 			continue
 		}
@@ -979,7 +1106,7 @@ func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg
 	}
 
 	if len(files) == 0 {
-		return nil, fmt.Errorf("dir %v contains no buildable, non-test .go files", pkg.dir)
+		return nil, fmt.Errorf("dir %v contains no buildable, non-test .go files", dir)
 	}
 
 	fset := token.NewFileSet()
@@ -990,7 +1117,7 @@ func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg
 		default:
 		}
 
-		fullFile := filepath.Join(pkg.dir, fi.Name())
+		fullFile := filepath.Join(dir, fi.Name())
 		f, err := parser.ParseFile(fset, fullFile, nil, 0)
 		if err != nil {
 			return nil, fmt.Errorf("parsing %s: %v", fullFile, err)
@@ -1002,7 +1129,7 @@ func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg
 			continue
 		}
 		if pkgName != expectPackage {
-			return nil, fmt.Errorf("scan of dir %v is not expected package %v (actually %v)", pkg.dir, expectPackage, pkgName)
+			return nil, fmt.Errorf("scan of dir %v is not expected package %v (actually %v)", dir, expectPackage, pkgName)
 		}
 		for name := range f.Scope.Objects {
 			if ast.IsExported(name) {
@@ -1017,14 +1144,14 @@ func loadExports(ctx context.Context, env *ProcessEnv, expectPackage string, pkg
 			exportList = append(exportList, k)
 		}
 		sort.Strings(exportList)
-		log.Printf("loaded exports in dir %v (package %v): %v", pkg.dir, expectPackage, strings.Join(exportList, ", "))
+		env.Logf("loaded exports in dir %v (package %v): %v", dir, expectPackage, strings.Join(exportList, ", "))
 	}
 	return exports, nil
 }
 
 // findImport searches for a package with the given symbols.
 // If no package is found, findImport returns ("", false, nil)
-func findImport(ctx context.Context, env *ProcessEnv, dirScan []*pkg, pkgName string, symbols map[string]bool, filename string) (*pkg, error) {
+func findImport(ctx context.Context, pass *pass, dirScan []*pkg, pkgName string, symbols map[string]bool, filename string) (*pkg, error) {
 	pkgDir, err := filepath.Abs(filename)
 	if err != nil {
 		return nil, err
@@ -1034,7 +1161,12 @@ func findImport(ctx context.Context, env *ProcessEnv, dirScan []*pkg, pkgName st
 	// Find candidate packages, looking only at their directory names first.
 	var candidates []pkgDistance
 	for _, pkg := range dirScan {
-		if pkg.dir != pkgDir && pkgIsCandidate(filename, pkgName, pkg) {
+		if pkg.dir == pkgDir && pass.f.Name.Name == pkgName {
+			// The candidate is in the same directory and has the
+			// same package name. Don't try to import ourselves.
+			continue
+		}
+		if pkgIsCandidate(filename, pkgName, pkg) {
 			candidates = append(candidates, pkgDistance{
 				pkg:      pkg,
 				distance: distance(pkgDir, pkg.dir),
@@ -1047,9 +1179,9 @@ func findImport(ctx context.Context, env *ProcessEnv, dirScan []*pkg, pkgName st
 	// ones.  Note that this sorts by the de-vendored name, so
 	// there's no "penalty" for vendoring.
 	sort.Sort(byDistanceOrImportPathShortLength(candidates))
-	if env.Debug {
+	if pass.env.Debug {
 		for i, c := range candidates {
-			log.Printf("%s candidate %d/%d: %v in %v", pkgName, i+1, len(candidates), c.pkg.importPathShort, c.pkg.dir)
+			pass.env.Logf("%s candidate %d/%d: %v in %v", pkgName, i+1, len(candidates), c.pkg.importPathShort, c.pkg.dir)
 		}
 	}
 
@@ -1086,10 +1218,13 @@ func findImport(ctx context.Context, env *ProcessEnv, dirScan []*pkg, pkgName st
 					wg.Done()
 				}()
 
-				exports, err := loadExports(ctx, env, pkgName, c.pkg)
+				if pass.env.Debug {
+					pass.env.Logf("loading exports in dir %s (seeking package %s)", c.pkg.dir, pkgName)
+				}
+				exports, err := pass.env.GetResolver().loadExports(ctx, pkgName, c.pkg)
 				if err != nil {
-					if env.Debug {
+					if pass.env.Debug {
-						log.Printf("loading exports in dir %s (seeking package %s): %v", c.pkg.dir, pkgName, err)
+						pass.env.Logf("loading exports in dir %s (seeking package %s): %v", c.pkg.dir, pkgName, err)
 					}
 					resc <- nil
 					return

vendor/golang.org/x/tools/internal/imports/imports.go

@@ -13,12 +13,14 @@ import (
 	"bytes"
 	"fmt"
 	"go/ast"
+	"go/build"
 	"go/format"
 	"go/parser"
 	"go/printer"
 	"go/token"
 	"io"
 	"io/ioutil"
+	"log"
 	"regexp"
 	"strconv"
 	"strings"
@@ -41,13 +43,10 @@ type Options struct {
 }
 
 // Process implements golang.org/x/tools/imports.Process with explicit context in env.
-func Process(filename string, src []byte, opt *Options) ([]byte, error) {
+func Process(filename string, src []byte, opt *Options) (formatted []byte, err error) {
-	if src == nil {
+	src, opt, err = initialize(filename, src, opt)
-		b, err := ioutil.ReadFile(filename)
+	if err != nil {
-		if err != nil {
+		return nil, err
-			return nil, err
-		}
-		src = b
 	}
 
 	fileSet := token.NewFileSet()
@@ -61,7 +60,93 @@ func Process(filename string, src []byte, opt *Options) ([]byte, error) {
 			return nil, err
 		}
 	}
+	return formatFile(fileSet, file, src, adjust, opt)
+}
 
+// FixImports returns a list of fixes to the imports that, when applied,
+// will leave the imports in the same state as Process.
+//
+// Note that filename's directory influences which imports can be chosen,
+// so it is important that filename be accurate.
+func FixImports(filename string, src []byte, opt *Options) (fixes []*ImportFix, err error) {
+	src, opt, err = initialize(filename, src, opt)
+	if err != nil {
+		return nil, err
+	}
+
+	fileSet := token.NewFileSet()
+	file, _, err := parse(fileSet, filename, src, opt)
+	if err != nil {
+		return nil, err
+	}
+
+	return getFixes(fileSet, file, filename, opt.Env)
+}
+
+// ApplyFix will apply all of the fixes to the file and format it.
+func ApplyFixes(fixes []*ImportFix, filename string, src []byte, opt *Options) (formatted []byte, err error) {
+	src, opt, err = initialize(filename, src, opt)
+	if err != nil {
+		return nil, err
+	}
+
+	fileSet := token.NewFileSet()
+	file, adjust, err := parse(fileSet, filename, src, opt)
+	if err != nil {
+		return nil, err
+	}
+
+	// Apply the fixes to the file.
+	apply(fileSet, file, fixes)
+
+	return formatFile(fileSet, file, src, adjust, opt)
+}
+
+// GetAllCandidates gets all of the standard library candidate packages to import in
+// sorted order on import path.
+func GetAllCandidates(filename string, opt *Options) (pkgs []ImportFix, err error) {
+	_, opt, err = initialize(filename, []byte{}, opt)
+	if err != nil {
+		return nil, err
+	}
+	return getAllCandidates(filename, opt.Env)
+}
+
+// initialize sets the values for opt and src.
+// If they are provided, they are not changed. Otherwise opt is set to the
+// default values and src is read from the file system.
+func initialize(filename string, src []byte, opt *Options) ([]byte, *Options, error) {
+	// Use defaults if opt is nil.
+	if opt == nil {
+		opt = &Options{Comments: true, TabIndent: true, TabWidth: 8}
+	}
+
+	// Set the env if the user has not provided it.
+	if opt.Env == nil {
+		opt.Env = &ProcessEnv{
+			GOPATH: build.Default.GOPATH,
+			GOROOT: build.Default.GOROOT,
+		}
+	}
+
+	// Set the logger if the user has not provided it.
+	if opt.Env.Logf == nil {
+		opt.Env.Logf = log.Printf
+	}
+
+	if src == nil {
+		b, err := ioutil.ReadFile(filename)
+		if err != nil {
+			return nil, nil, err
+		}
+		src = b
+	}
+
+	return src, opt, nil
+}
+
+func formatFile(fileSet *token.FileSet, file *ast.File, src []byte, adjust func(orig []byte, src []byte) []byte, opt *Options) ([]byte, error) {
+	mergeImports(opt.Env, fileSet, file)
 	sortImports(opt.Env, fileSet, file)
 	imps := astutil.Imports(fileSet, file)
 	var spacesBefore []string // import paths we need spaces before
@@ -89,7 +174,7 @@ func Process(filename string, src []byte, opt *Options) ([]byte, error) {
 	printConfig := &printer.Config{Mode: printerMode, Tabwidth: opt.TabWidth}
 
 	var buf bytes.Buffer
-	err = printConfig.Fprint(&buf, fileSet, file)
+	err := printConfig.Fprint(&buf, fileSet, file)
 	if err != nil {
 		return nil, err
 	}

vendor/golang.org/x/tools/internal/imports/mod.go

@@ -2,9 +2,10 @@ package imports
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
-	"log"
 	"os"
 	"path"
 	"path/filepath"
@@ -19,37 +20,41 @@ import (
 	"golang.org/x/tools/internal/module"
 )
 
-// moduleResolver implements resolver for modules using the go command as little
+// ModuleResolver implements resolver for modules using the go command as little
 // as feasible.
-type moduleResolver struct {
+type ModuleResolver struct {
-	env *ProcessEnv
+	env            *ProcessEnv
+	moduleCacheDir string
 
-	initialized   bool
+	Initialized   bool
-	main          *moduleJSON
+	Main          *ModuleJSON
-	modsByModPath []*moduleJSON // All modules, ordered by # of path components in module Path...
+	ModsByModPath []*ModuleJSON // All modules, ordered by # of path components in module Path...
-	modsByDir     []*moduleJSON // ...or Dir.
+	ModsByDir     []*ModuleJSON // ...or Dir.
+
+	// moduleCacheInfo stores information about the module cache.
+	moduleCacheInfo *moduleCacheInfo
 }
 
-type moduleJSON struct {
+type ModuleJSON struct {
 	Path     string           // module path
 	Version  string           // module version
 	Versions []string         // available module versions (with -versions)
-	Replace  *moduleJSON      // replaced by this module
+	Replace  *ModuleJSON      // replaced by this module
 	Time     *time.Time       // time version was created
-	Update   *moduleJSON      // available update, if any (with -u)
+	Update   *ModuleJSON      // available update, if any (with -u)
 	Main     bool             // is this the main module?
 	Indirect bool             // is this module only an indirect dependency of main module?
 	Dir      string           // directory holding files for this module, if any
 	GoMod    string           // path to go.mod file for this module, if any
-	Error    *moduleErrorJSON // error loading module
+	Error    *ModuleErrorJSON // error loading module
 }
 
-type moduleErrorJSON struct {
+type ModuleErrorJSON struct {
 	Err string // the error itself
 }
 
-func (r *moduleResolver) init() error {
+func (r *ModuleResolver) init() error {
-	if r.initialized {
+	if r.Initialized {
 		return nil
 	}
 	stdout, err := r.env.invokeGo("list", "-m", "-json", "...")
@@ -57,54 +62,71 @@ func (r *moduleResolver) init() error {
 		return err
 	}
 	for dec := json.NewDecoder(stdout); dec.More(); {
-		mod := &moduleJSON{}
+		mod := &ModuleJSON{}
 		if err := dec.Decode(mod); err != nil {
 			return err
 		}
 		if mod.Dir == "" {
 			if r.env.Debug {
-				log.Printf("module %v has not been downloaded and will be ignored", mod.Path)
+				r.env.Logf("module %v has not been downloaded and will be ignored", mod.Path)
 			}
 			// Can't do anything with a module that's not downloaded.
 			continue
 		}
-		r.modsByModPath = append(r.modsByModPath, mod)
+		r.ModsByModPath = append(r.ModsByModPath, mod)
-		r.modsByDir = append(r.modsByDir, mod)
+		r.ModsByDir = append(r.ModsByDir, mod)
 		if mod.Main {
-			r.main = mod
+			r.Main = mod
 		}
 	}
 
-	sort.Slice(r.modsByModPath, func(i, j int) bool {
+	sort.Slice(r.ModsByModPath, func(i, j int) bool {
 		count := func(x int) int {
-			return strings.Count(r.modsByModPath[x].Path, "/")
+			return strings.Count(r.ModsByModPath[x].Path, "/")
 		}
 		return count(j) < count(i) // descending order
 	})
-	sort.Slice(r.modsByDir, func(i, j int) bool {
+	sort.Slice(r.ModsByDir, func(i, j int) bool {
 		count := func(x int) int {
-			return strings.Count(r.modsByDir[x].Dir, "/")
+			return strings.Count(r.ModsByDir[x].Dir, "/")
 		}
 		return count(j) < count(i) // descending order
 	})
 
-	r.initialized = true
+	if r.moduleCacheInfo == nil {
+		r.moduleCacheInfo = &moduleCacheInfo{
+			modCacheDirInfo: make(map[string]*directoryPackageInfo),
+		}
+	}
+
+	r.Initialized = true
 	return nil
 }
 
 // findPackage returns the module and directory that contains the package at
 // the given import path, or returns nil, "" if no module is in scope.
-func (r *moduleResolver) findPackage(importPath string) (*moduleJSON, string) {
+func (r *ModuleResolver) findPackage(importPath string) (*ModuleJSON, string) {
-	for _, m := range r.modsByModPath {
+	for _, m := range r.ModsByModPath {
 		if !strings.HasPrefix(importPath, m.Path) {
 			continue
 		}
 		pathInModule := importPath[len(m.Path):]
 		pkgDir := filepath.Join(m.Dir, pathInModule)
-		if dirIsNestedModule(pkgDir, m) {
+		if r.dirIsNestedModule(pkgDir, m) {
 			continue
 		}
 
+		if info, ok := r.moduleCacheInfo.Load(pkgDir); ok {
+			if packageScanned, err := info.reachedStatus(directoryScanned); packageScanned {
+				if err != nil {
+					// There was some error with scanning this directory.
+					// It does not contain a valid package.
+					continue
+				}
+				return m, pkgDir
+			}
+		}
+
 		pkgFiles, err := ioutil.ReadDir(pkgDir)
 		if err != nil {
 			continue
@@ -124,7 +146,7 @@ func (r *moduleResolver) findPackage(importPath string) (*moduleJSON, string) {
 
 // findModuleByDir returns the module that contains dir, or nil if no such
 // module is in scope.
-func (r *moduleResolver) findModuleByDir(dir string) *moduleJSON {
+func (r *ModuleResolver) findModuleByDir(dir string) *ModuleJSON {
 	// This is quite tricky and may not be correct. dir could be:
 	// - a package in the main module.
 	// - a replace target underneath the main module's directory.
@@ -135,12 +157,12 @@ func (r *moduleResolver) findModuleByDir(dir string) *moduleJSON {
 	// - in /vendor/ in -mod=vendor mode.
 	//    - nested module? Dunno.
 	// Rumor has it that replace targets cannot contain other replace targets.
-	for _, m := range r.modsByDir {
+	for _, m := range r.ModsByDir {
 		if !strings.HasPrefix(dir, m.Dir) {
 			continue
 		}
 
-		if dirIsNestedModule(dir, m) {
+		if r.dirIsNestedModule(dir, m) {
 			continue
 		}
 
@@ -151,18 +173,28 @@ func (r *moduleResolver) findModuleByDir(dir string) *moduleJSON {
 
 // dirIsNestedModule reports if dir is contained in a nested module underneath
 // mod, not actually in mod.
-func dirIsNestedModule(dir string, mod *moduleJSON) bool {
+func (r *ModuleResolver) dirIsNestedModule(dir string, mod *ModuleJSON) bool {
 	if !strings.HasPrefix(dir, mod.Dir) {
 		return false
 	}
-	mf := findModFile(dir)
+	if r.dirInModuleCache(dir) {
+		// Nested modules in the module cache are pruned,
+		// so it cannot be a nested module.
+		return false
+	}
+	mf := r.findModFile(dir)
 	if mf == "" {
 		return false
 	}
 	return filepath.Dir(mf) != mod.Dir
 }
 
-func findModFile(dir string) string {
+func (r *ModuleResolver) findModFile(dir string) string {
+	if r.dirInModuleCache(dir) {
+		matches := modCacheRegexp.FindStringSubmatch(dir)
+		index := strings.Index(dir, matches[1]+"@"+matches[2])
+		return filepath.Join(dir[:index], matches[1]+"@"+matches[2], "go.mod")
+	}
 	for {
 		f := filepath.Join(dir, "go.mod")
 		info, err := os.Stat(f)
@@ -177,7 +209,14 @@ func findModFile(dir string) string {
 	}
 }
 
-func (r *moduleResolver) loadPackageNames(importPaths []string, srcDir string) (map[string]string, error) {
+func (r *ModuleResolver) dirInModuleCache(dir string) bool {
+	if r.moduleCacheDir == "" {
+		return false
+	}
+	return strings.HasPrefix(dir, r.moduleCacheDir)
+}
+
+func (r *ModuleResolver) loadPackageNames(importPaths []string, srcDir string) (map[string]string, error) {
 	if err := r.init(); err != nil {
 		return nil, err
 	}
@@ -196,7 +235,7 @@ func (r *moduleResolver) loadPackageNames(importPaths []string, srcDir string) (
 	return names, nil
 }
 
-func (r *moduleResolver) scan(_ references) ([]*pkg, error) {
+func (r *ModuleResolver) scan(_ references) ([]*pkg, error) {
 	if err := r.init(); err != nil {
 		return nil, err
 	}
@@ -205,15 +244,16 @@ func (r *moduleResolver) scan(_ references) ([]*pkg, error) {
 	roots := []gopathwalk.Root{
 		{filepath.Join(r.env.GOROOT, "/src"), gopathwalk.RootGOROOT},
 	}
-	if r.main != nil {
+	if r.Main != nil {
-		roots = append(roots, gopathwalk.Root{r.main.Dir, gopathwalk.RootCurrentModule})
+		roots = append(roots, gopathwalk.Root{r.Main.Dir, gopathwalk.RootCurrentModule})
 	}
-	for _, p := range filepath.SplitList(r.env.GOPATH) {
+	if r.moduleCacheDir == "" {
-		roots = append(roots, gopathwalk.Root{filepath.Join(p, "/pkg/mod"), gopathwalk.RootModuleCache})
+		r.moduleCacheDir = filepath.Join(filepath.SplitList(r.env.GOPATH)[0], "/pkg/mod")
 	}
+	roots = append(roots, gopathwalk.Root{r.moduleCacheDir, gopathwalk.RootModuleCache})
 
 	// Walk replace targets, just in case they're not in any of the above.
-	for _, mod := range r.modsByModPath {
+	for _, mod := range r.ModsByModPath {
 		if mod.Replace != nil {
 			roots = append(roots, gopathwalk.Root{mod.Dir, gopathwalk.RootOther})
 		}
@@ -223,90 +263,181 @@ func (r *moduleResolver) scan(_ references) ([]*pkg, error) {
 	dupCheck := make(map[string]bool)
 	var mu sync.Mutex
 
-	gopathwalk.Walk(roots, func(root gopathwalk.Root, dir string) {
+	// Packages in the module cache are immutable. If we have
+	// already seen this package on a previous scan of the module
+	// cache, return that result.
+	skip := func(root gopathwalk.Root, dir string) bool {
 		mu.Lock()
 		defer mu.Unlock()
+		// If we have already processed this directory on this walk, skip it.
+		if _, dup := dupCheck[dir]; dup {
+			return true
+		}
 
+		// If we have saved this directory information, skip it.
+		info, ok := r.moduleCacheInfo.Load(dir)
+		if !ok {
+			return false
+		}
+		// This directory can be skipped as long as we have already scanned it.
+		// Packages with errors will continue to have errors, so there is no need
+		// to rescan them.
+		packageScanned, _ := info.reachedStatus(directoryScanned)
+		return packageScanned
+	}
+
+	add := func(root gopathwalk.Root, dir string) {
+		mu.Lock()
+		defer mu.Unlock()
 		if _, dup := dupCheck[dir]; dup {
 			return
 		}
 
-		dupCheck[dir] = true
+		info, err := r.scanDirForPackage(root, dir)
-
+		if err != nil {
-		subdir := ""
-		if dir != root.Path {
-			subdir = dir[len(root.Path)+len("/"):]
-		}
-		importPath := filepath.ToSlash(subdir)
-		if strings.HasPrefix(importPath, "vendor/") {
-			// Ignore vendor dirs. If -mod=vendor is on, then things
-			// should mostly just work, but when it's not vendor/
-			// is a mess. There's no easy way to tell if it's on.
-			// We can still find things in the mod cache and
-			// map them into /vendor when -mod=vendor is on.
 			return
 		}
-		switch root.Type {
+		if root.Type == gopathwalk.RootModuleCache {
-		case gopathwalk.RootCurrentModule:
+			// Save this package information in the cache and return.
-			importPath = path.Join(r.main.Path, filepath.ToSlash(subdir))
+			// Packages from the module cache are added after Walk.
-		case gopathwalk.RootModuleCache:
+			r.moduleCacheInfo.Store(dir, info)
-			matches := modCacheRegexp.FindStringSubmatch(subdir)
+			return
-			modPath, err := module.DecodePath(filepath.ToSlash(matches[1]))
-			if err != nil {
-				if r.env.Debug {
-					log.Printf("decoding module cache path %q: %v", subdir, err)
-				}
-				return
-			}
-			importPath = path.Join(modPath, filepath.ToSlash(matches[3]))
-		case gopathwalk.RootGOROOT:
-			importPath = subdir
 		}
 
-		// Check if the directory is underneath a module that's in scope.
+		// Skip this package if there was an error loading package info.
-		if mod := r.findModuleByDir(dir); mod != nil {
+		if info.err != nil {
-			// It is. If dir is the target of a replace directive,
+			return
-			// our guessed import path is wrong. Use the real one.
-			if mod.Dir == dir {
-				importPath = mod.Path
-			} else {
-				dirInMod := dir[len(mod.Dir)+len("/"):]
-				importPath = path.Join(mod.Path, filepath.ToSlash(dirInMod))
-			}
-		} else {
-			// The package is in an unknown module. Check that it's
-			// not obviously impossible to import.
-			var modFile string
-			switch root.Type {
-			case gopathwalk.RootModuleCache:
-				matches := modCacheRegexp.FindStringSubmatch(subdir)
-				modFile = filepath.Join(matches[1], "@", matches[2], "go.mod")
-			default:
-				modFile = findModFile(dir)
-			}
-
-			modBytes, err := ioutil.ReadFile(modFile)
-			if err == nil && !strings.HasPrefix(importPath, modulePath(modBytes)) {
-				// The module's declared path does not match
-				// its expected path. It probably needs a
-				// replace directive we don't have.
-				return
-			}
-		}
-		// We may have discovered a package that has a different version
-		// in scope already. Canonicalize to that one if possible.
-		if _, canonicalDir := r.findPackage(importPath); canonicalDir != "" {
-			dir = canonicalDir
 		}
 
-		result = append(result, &pkg{
+		// The rest of this function canonicalizes the packages using the results
-			importPathShort: VendorlessPath(importPath),
+		// of initializing the resolver from 'go list -m'.
-			dir:             dir,
+		res, err := r.canonicalize(info.nonCanonicalImportPath, info.dir, info.needsReplace)
-		})
+		if err != nil {
-	}, gopathwalk.Options{Debug: r.env.Debug, ModulesEnabled: true})
+			return
+		}
+
+		result = append(result, res)
+	}
+
+	gopathwalk.WalkSkip(roots, add, skip, gopathwalk.Options{Debug: r.env.Debug, ModulesEnabled: true})
+
+	// Add the packages from the modules in the mod cache that were skipped.
+	for _, dir := range r.moduleCacheInfo.Keys() {
+		info, ok := r.moduleCacheInfo.Load(dir)
+		if !ok {
+			continue
+		}
+
+		// Skip this directory if we were not able to get the package information successfully.
+		if scanned, err := info.reachedStatus(directoryScanned); !scanned || err != nil {
+			continue
+		}
+
+		res, err := r.canonicalize(info.nonCanonicalImportPath, info.dir, info.needsReplace)
+		if err != nil {
+			continue
+		}
+		result = append(result, res)
+	}
+
 	return result, nil
 }
 
+// canonicalize gets the result of canonicalizing the packages using the results
+// of initializing the resolver from 'go list -m'.
+func (r *ModuleResolver) canonicalize(importPath, dir string, needsReplace bool) (res *pkg, err error) {
+	// Check if the directory is underneath a module that's in scope.
+	if mod := r.findModuleByDir(dir); mod != nil {
+		// It is. If dir is the target of a replace directive,
+		// our guessed import path is wrong. Use the real one.
+		if mod.Dir == dir {
+			importPath = mod.Path
+		} else {
+			dirInMod := dir[len(mod.Dir)+len("/"):]
+			importPath = path.Join(mod.Path, filepath.ToSlash(dirInMod))
+		}
+	} else if needsReplace {
+		return nil, fmt.Errorf("needed this package to be in scope: %s", dir)
+	}
+
+	// We may have discovered a package that has a different version
+	// in scope already. Canonicalize to that one if possible.
+	if _, canonicalDir := r.findPackage(importPath); canonicalDir != "" {
+		dir = canonicalDir
+	}
+	return &pkg{
+		importPathShort: VendorlessPath(importPath),
+		dir:             dir,
+	}, nil
+}
+
+func (r *ModuleResolver) loadExports(ctx context.Context, expectPackage string, pkg *pkg) (map[string]bool, error) {
+	if err := r.init(); err != nil {
+		return nil, err
+	}
+	return loadExportsFromFiles(ctx, r.env, expectPackage, pkg.dir)
+}
+
+func (r *ModuleResolver) scanDirForPackage(root gopathwalk.Root, dir string) (directoryPackageInfo, error) {
+	subdir := ""
+	if dir != root.Path {
+		subdir = dir[len(root.Path)+len("/"):]
+	}
+	importPath := filepath.ToSlash(subdir)
+	if strings.HasPrefix(importPath, "vendor/") {
+		// Ignore vendor dirs. If -mod=vendor is on, then things
+		// should mostly just work, but when it's not vendor/
+		// is a mess. There's no easy way to tell if it's on.
+		// We can still find things in the mod cache and
+		// map them into /vendor when -mod=vendor is on.
+		return directoryPackageInfo{}, fmt.Errorf("vendor directory")
+	}
+	switch root.Type {
+	case gopathwalk.RootCurrentModule:
+		importPath = path.Join(r.Main.Path, filepath.ToSlash(subdir))
+	case gopathwalk.RootModuleCache:
+		matches := modCacheRegexp.FindStringSubmatch(subdir)
+		if len(matches) == 0 {
+			return directoryPackageInfo{
+				status: directoryScanned,
+				err:    fmt.Errorf("invalid module cache path: %v", subdir),
+			}, nil
+		}
+		modPath, err := module.DecodePath(filepath.ToSlash(matches[1]))
+		if err != nil {
+			if r.env.Debug {
+				r.env.Logf("decoding module cache path %q: %v", subdir, err)
+			}
+			return directoryPackageInfo{
+				status: directoryScanned,
+				err:    fmt.Errorf("decoding module cache path %q: %v", subdir, err),
+			}, nil
+		}
+		importPath = path.Join(modPath, filepath.ToSlash(matches[3]))
+	case gopathwalk.RootGOROOT:
+		importPath = subdir
+	}
+
+	// Check that this package is not obviously impossible to import.
+	modFile := r.findModFile(dir)
+
+	var needsReplace bool
+	modBytes, err := ioutil.ReadFile(modFile)
+	if err == nil && !strings.HasPrefix(importPath, modulePath(modBytes)) {
+		// The module's declared path does not match
+		// its expected path. It probably needs a
+		// replace directive we don't have.
+		needsReplace = true
+	}
+
+	return directoryPackageInfo{
+		status:                 directoryScanned,
+		dir:                    dir,
+		nonCanonicalImportPath: importPath,
+		needsReplace:           needsReplace,
+	}, nil
+}
+
 // modCacheRegexp splits a path in a module cache into module, module version, and package.
 var modCacheRegexp = regexp.MustCompile(`(.*)@([^/\\]*)(.*)`)
 

vendor/golang.org/x/tools/internal/imports/mod_cache.go

@@ -0,0 +1,121 @@
+package imports
+
+import (
+	"sync"
+)
+
+// ModuleResolver implements Resolver for modules using the go command as little
+// as feasible.
+//
+// To find packages to import, the resolver needs to know about all of the
+// the packages that could be imported. This includes packages that are
+// already in modules that are in (1) the current module, (2) replace targets,
+// and (3) packages in the module cache. Packages in (1) and (2) may change over
+// time, as the client may edit the current module and locally replaced modules.
+// The module cache (which includes all of the packages in (3)) can only
+// ever be added to.
+//
+// The resolver can thus save state about packages in the module cache
+// and guarantee that this will not change over time. To obtain information
+// about new modules added to the module cache, the module cache should be
+// rescanned.
+//
+// It is OK to serve information about modules that have been deleted,
+// as they do still exist.
+// TODO(suzmue): can we share information with the caller about
+// what module needs to be downloaded to import this package?
+
+type directoryPackageStatus int
+
+const (
+	_ directoryPackageStatus = iota
+	directoryScanned
+)
+
+type directoryPackageInfo struct {
+	// status indicates the extent to which this struct has been filled in.
+	status directoryPackageStatus
+	// err is non-nil when there was an error trying to reach status.
+	err error
+
+	// Set when status > directoryScanned.
+
+	// dir is the absolute directory of this package.
+	dir string
+	// nonCanonicalImportPath is the expected import path for this package.
+	// This may not be an import path that can be used to import this package.
+	nonCanonicalImportPath string
+	// needsReplace is true if the nonCanonicalImportPath does not match the
+	// the modules declared path, making it impossible to import without a
+	// replace directive.
+	needsReplace bool
+}
+
+// reachedStatus returns true when info has a status at least target and any error associated with
+// an attempt to reach target.
+func (info *directoryPackageInfo) reachedStatus(target directoryPackageStatus) (bool, error) {
+	if info.err == nil {
+		return info.status >= target, nil
+	}
+	if info.status == target {
+		return true, info.err
+	}
+	return true, nil
+}
+
+// moduleCacheInfo is a concurrency safe map for storing information about
+// the directories in the module cache.
+//
+// The information in this cache is built incrementally. Entries are initialized in scan.
+// No new keys should be added in any other functions, as all directories containing
+// packages are identified in scan.
+//
+// Other functions, including loadExports and findPackage, may update entries in this cache
+// as they discover new things about the directory.
+//
+// We do not need to protect the data in the cache for multiple writes, because it only stores
+// module cache directories, which do not change. If two competing stores take place, there will be
+// one store that wins. Although this could result in a loss of information it will not be incorrect
+// and may just result in recomputing the same result later.
+//
+// TODO(suzmue): consider other concurrency strategies and data structures (RWLocks, sync.Map, etc)
+type moduleCacheInfo struct {
+	mu sync.Mutex
+	// modCacheDirInfo stores information about packages in
+	// module cache directories. Keyed by absolute directory.
+	modCacheDirInfo map[string]*directoryPackageInfo
+}
+
+// Store stores the package info for dir.
+func (d *moduleCacheInfo) Store(dir string, info directoryPackageInfo) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.modCacheDirInfo[dir] = &directoryPackageInfo{
+		status:                 info.status,
+		err:                    info.err,
+		dir:                    info.dir,
+		nonCanonicalImportPath: info.nonCanonicalImportPath,
+		needsReplace:           info.needsReplace,
+	}
+}
+
+// Load returns a copy of the directoryPackageInfo for absolute directory dir.
+func (d *moduleCacheInfo) Load(dir string) (directoryPackageInfo, bool) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	info, ok := d.modCacheDirInfo[dir]
+	if !ok {
+		return directoryPackageInfo{}, false
+	}
+	return *info, true
+}
+
+// Keys returns the keys currently present in d.
+func (d *moduleCacheInfo) Keys() (keys []string) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	for key := range d.modCacheDirInfo {
+		keys = append(keys, key)
+	}
+	return keys
+}

vendor/golang.org/x/tools/internal/imports/sortimports.go

@@ -58,6 +58,53 @@ func sortImports(env *ProcessEnv, fset *token.FileSet, f *ast.File) {
 	}
 }
 
+// mergeImports merges all the import declarations into the first one.
+// Taken from golang.org/x/tools/ast/astutil.
+func mergeImports(env *ProcessEnv, fset *token.FileSet, f *ast.File) {
+	if len(f.Decls) <= 1 {
+		return
+	}
+
+	// Merge all the import declarations into the first one.
+	var first *ast.GenDecl
+	for i := 0; i < len(f.Decls); i++ {
+		decl := f.Decls[i]
+		gen, ok := decl.(*ast.GenDecl)
+		if !ok || gen.Tok != token.IMPORT || declImports(gen, "C") {
+			continue
+		}
+		if first == nil {
+			first = gen
+			continue // Don't touch the first one.
+		}
+		// We now know there is more than one package in this import
+		// declaration. Ensure that it ends up parenthesized.
+		first.Lparen = first.Pos()
+		// Move the imports of the other import declaration to the first one.
+		for _, spec := range gen.Specs {
+			spec.(*ast.ImportSpec).Path.ValuePos = first.Pos()
+			first.Specs = append(first.Specs, spec)
+		}
+		f.Decls = append(f.Decls[:i], f.Decls[i+1:]...)
+		i--
+	}
+}
+
+// declImports reports whether gen contains an import of path.
+// Taken from golang.org/x/tools/ast/astutil.
+func declImports(gen *ast.GenDecl, path string) bool {
+	if gen.Tok != token.IMPORT {
+		return false
+	}
+	for _, spec := range gen.Specs {
+		impspec := spec.(*ast.ImportSpec)
+		if importPath(impspec) == path {
+			return true
+		}
+	}
+	return false
+}
+
 func importPath(s ast.Spec) string {
 	t, err := strconv.Unquote(s.(*ast.ImportSpec).Path.Value)
 	if err == nil {

vendor/modules.txt

@@ -196,7 +196,7 @@ golang.org/x/sys/windows
 golang.org/x/text/width
 golang.org/x/text/transform
 golang.org/x/text/unicode/norm
-# golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd
+# golang.org/x/tools v0.0.0-20190521203540-521d6ed310dd => github.com/golangci/tools v0.0.0-20190713050349-979bdb7f8cc8
 golang.org/x/tools/go/analysis
 golang.org/x/tools/go/analysis/passes/asmdecl
 golang.org/x/tools/go/analysis/passes/assign