doc: improve documentation about debugging. (#3434)

docs/src/docs/contributing/debug.mdx

@@ -4,12 +4,21 @@ title: Debugging
 
 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:
+```bash
+golangci-lint run -v
+```
 
-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.
+If you would like to see more detailed logs you can use the environment variable `GL_DEBUG`.
+Its value is a list of debug tags.
+
+The existing debug tags are documented in the following file: https://github.com/golangci/golangci-lint/blob/master/pkg/logutils/logutils.go
+
+For example:
+
+```bash
+GL_DEBUG="loader,gocritic" golangci-lint run
+```
+
+```bash
+GL_DEBUG="loader,env" golangci-lint run
+```

pkg/logutils/logutils.go

@@ -13,12 +13,12 @@ import (
 const envDebug = "GL_DEBUG"
 
 const (
-	DebugKeyAutogenExclude     = "autogen_exclude"
+	DebugKeyAutogenExclude     = "autogen_exclude" // Debugs a filter excluding autogenerated source code.
 	DebugKeyBinSalt            = "bin_salt"
 	DebugKeyConfigReader       = "config_reader"
 	DebugKeyEmpty              = ""
 	DebugKeyEnabledLinters     = "enabled_linters"
-	DebugKeyEnv                = "env"
+	DebugKeyEnv                = "env" // Debugs `go env` command.
 	DebugKeyExcludeRules       = "exclude_rules"
 	DebugKeyExec               = "exec"
 	DebugKeyFilenameUnadjuster = "filename_unadjuster"
@@ -27,7 +27,7 @@ const (
 	DebugKeyLintersContext     = "linters_context"
 	DebugKeyLintersDB          = "lintersdb"
 	DebugKeyLintersOutput      = "linters_output"
-	DebugKeyLoader             = "loader"
+	DebugKeyLoader             = "loader" // Debugs packages loading (including `go/packages` internal debugging).
 	DebugKeyMaxFromLinter      = "max_from_linter"
 	DebugKeyMaxSameIssues      = "max_same_issues"
 	DebugKeyPkgCache           = "pkgcache"
@@ -55,10 +55,10 @@ const (
 )
 
 const (
-	DebugKeyGoCritic  = "gocritic"
-	DebugKeyMegacheck = "megacheck"
-	DebugKeyNolint    = "nolint"
-	DebugKeyRevive    = "revive"
+	DebugKeyGoCritic  = "gocritic"  // Debugs `go-critic` linter.
+	DebugKeyMegacheck = "megacheck" // Debugs `staticcheck` related linters.
+	DebugKeyNolint    = "nolint"    // Debugs a filter excluding issues by `//nolint` comments.
+	DebugKeyRevive    = "revive"    // Debugs `revice` linter.
 )
 
 func getEnabledDebugs() map[string]bool {