feat: colored diff for fmt command

go.mod

@@ -15,6 +15,7 @@ require (
 	github.com/Djarvur/go-err113 v0.0.0-20210108212216-aea10b59be24
 	github.com/GaijinEntertainment/go-exhaustruct/v3 v3.3.1
 	github.com/OpenPeeDeeP/depguard/v2 v2.2.1
+	github.com/alecthomas/chroma/v2 v2.15.0
 	github.com/alecthomas/go-check-sumtype v0.3.1
 	github.com/alexkohler/nakedret/v2 v2.0.6
 	github.com/alexkohler/prealloc v1.0.0
@@ -148,6 +149,7 @@ require (
 	github.com/chavacava/garif v0.1.0 // indirect
 	github.com/dave/dst v0.27.3 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/dlclark/regexp2 v1.11.4 // indirect
 	github.com/ebitengine/purego v0.8.2 // indirect
 	github.com/ettle/strcase v0.2.0 // indirect
 	github.com/fatih/structtag v1.2.0 // indirect

pkg/commands/fmt.go

@@ -20,8 +20,9 @@ import (
 type fmtOptions struct {
 	config.LoaderOptions
 
-	diff  bool // Flag only.
-	stdin bool // Flag only.
+	diff        bool // Flag only.
+	diffColored bool // Flag only.
+	stdin       bool // Flag only.
 }
 
 type fmtCommand struct {
@@ -70,6 +71,7 @@ func newFmtCommand(logger logutils.Log, info BuildInfo) *fmtCommand {
 	setupFormattersFlagSet(c.viper, fs)
 
 	fs.BoolVarP(&c.opts.diff, "diff", "d", false, color.GreenString("Display diffs instead of rewriting files"))
+	fs.BoolVar(&c.opts.diffColored, "diff-colored", false, color.GreenString("Display diffs instead of rewriting files (with colors)"))
 	fs.BoolVar(&c.opts.stdin, "stdin", false, color.GreenString("Use standard input for piping source files"))
 
 	c.cmd = fmtCmd
@@ -102,7 +104,7 @@ func (c *fmtCommand) preRunE(_ *cobra.Command, _ []string) error {
 
 	matcher := processors.NewGeneratedFileMatcher(c.cfg.Formatters.Exclusions.Generated)
 
-	opts, err := goformat.NewRunnerOptions(c.cfg, c.opts.diff, c.opts.stdin)
+	opts, err := goformat.NewRunnerOptions(c.cfg, c.opts.diff, c.opts.diffColored, c.opts.stdin)
 	if err != nil {
 		return fmt.Errorf("build walk options: %w", err)
 	}

pkg/goformat/runner.go

@@ -12,6 +12,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/alecthomas/chroma/v2/quick"
 	rpdiff "github.com/rogpeppe/go-internal/diff"
 
 	"github.com/golangci/golangci-lint/v2/pkg/config"
@@ -128,9 +129,19 @@ func (c *Runner) process(path string, stdout io.Writer, in io.Reader) error {
 	if c.opts.diff {
 		newName := filepath.ToSlash(path)
 		oldName := newName + ".orig"
-		_, err = stdout.Write(rpdiff.Diff(oldName, input, newName, output))
-		if err != nil {
-			return err
+
+		patch := rpdiff.Diff(oldName, input, newName, output)
+
+		if c.opts.colors {
+			err = quick.Highlight(stdout, string(patch), "diff", "terminal", "native")
+			if err != nil {
+				return err
+			}
+		} else {
+			_, err = stdout.Write(patch)
+			if err != nil {
+				return err
+			}
 		}
 
 		c.exitCode = 1
@@ -168,10 +179,11 @@ type RunnerOptions struct {
 	patterns  []*regexp.Regexp
 	generated string
 	diff      bool
+	colors    bool
 	stdin     bool
 }
 
-func NewRunnerOptions(cfg *config.Config, diff, stdin bool) (RunnerOptions, error) {
+func NewRunnerOptions(cfg *config.Config, diff, diffColored, stdin bool) (RunnerOptions, error) {
 	basePath, err := fsutils.GetBasePath(context.Background(), cfg.Run.RelativePathMode, cfg.GetConfigDir())
 	if err != nil {
 		return RunnerOptions{}, fmt.Errorf("get base path: %w", err)
@@ -180,7 +192,8 @@ func NewRunnerOptions(cfg *config.Config, diff, stdin bool) (RunnerOptions, erro
 	opts := RunnerOptions{
 		basePath:  basePath,
 		generated: cfg.Formatters.Exclusions.Generated,
-		diff:      diff,
+		diff:      diff || diffColored,
+		colors:    diffColored,
 		stdin:     stdin,
 	}