Print first compilation error in warning about inability to run megacheck because of compilation errors

pkg/golinters/megacheck.go

@@ -2,10 +2,12 @@ package golinters
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strings"
 
 	megacheckAPI "github.com/golangci/go-tools/cmd/megacheck"
+	"github.com/golangci/golangci-lint/pkg/fsutils"
 	"github.com/golangci/golangci-lint/pkg/lint/linter"
 	"github.com/golangci/golangci-lint/pkg/result"
 )
@@ -50,14 +52,45 @@ func (m Megacheck) Desc() string {
 	return descs[m.Name()]
 }
 
+func prettifyCompilationError(err error) error {
+	i := TypeCheck{}.parseError(err)
+	if i == nil {
+		return err
+	}
+
+	shortFilename, pathErr := fsutils.ShortestRelPath(i.Pos.Filename, "")
+	if pathErr != nil {
+		return err
+	}
+
+	errText := shortFilename
+	if i.Line() != 0 {
+		errText += fmt.Sprintf(":%d", i.Line())
+	}
+	errText += fmt.Sprintf(": %s", i.Text)
+	return errors.New(errText)
+}
+
 func (m Megacheck) Run(ctx context.Context, lintCtx *linter.Context) ([]result.Issue, error) {
 	if len(lintCtx.NotCompilingPackages) != 0 {
 		var packages []string
+		var errors []error
 		for _, p := range lintCtx.NotCompilingPackages {
 			packages = append(packages, p.String())
+			errors = append(errors, p.Errors...)
 		}
-		lintCtx.Log.Warnf("Can't run megacheck because of compilation errors in packages "+
+
-			"%s: run `typecheck` linter to see errors", packages)
+		warnText := fmt.Sprintf("Can't run megacheck because of compilation errors in packages %s",
+			packages)
+		if len(errors) != 0 {
+			warnText += fmt.Sprintf(": %s", prettifyCompilationError(errors[0]))
+			if len(errors) > 1 {
+				const runCmd = "golangci-lint run --no-config --disable-all -E typecheck"
+				warnText += fmt.Sprintf(" and %d more errors: run `%s` to see all errors", len(errors)-1, runCmd)
+			}
+		}
+		lintCtx.Log.Warnf("%s", warnText)
+
 		// megacheck crashes if there are not compiling packages
 		return nil, nil
 	}

pkg/result/processors/diff.go

@@ -43,7 +43,7 @@ func (p Diff) Process(issues []result.Issue) ([]result.Issue, error) {
 	if p.patchFilePath != "" {
 		patch, err := ioutil.ReadFile(p.patchFilePath)
 		if err != nil {
-			return nil, fmt.Errorf("can't read from pathc file %s: %s", p.patchFilePath, err)
+			return nil, fmt.Errorf("can't read from patch file %s: %s", p.patchFilePath, err)
 		}
 		patchReader = bytes.NewReader(patch)
 	} else if p.patch != "" {