add support for Go 1.25 ignore directives

Much like vendor and testdata directories, we still support
formatting directories or files within them as long as they are given
as explicit arguments.

Fixes #250.
Closes #329 as resolved.

Author: mvdan

README.md

@@ -23,6 +23,9 @@ The [added formatting rules](#Added-rules) are implemented in the `format` packa
 Similarly, the added rules do not apply to generated Go files unless they are
 given as explicit arguments.
 
+[`ignore` directives](https://go.dev/ref/mod#go-mod-file-ignore) in `go.mod` files are obeyed as well,
+unless directories or files within them are given as explicit arguments.
+
 Finally, note that the `-r` rewrite flag is removed in favor of `gofmt -r`,
 and the `-s` flag is hidden as it is always enabled.
 

gofmt.go

@@ -521,11 +521,8 @@ func gofmtMain(s *sequencer) {
 			case err != nil:
 				return err
 			case d.IsDir():
-				if !explicit {
-					switch filepath.Base(path) {
-					case "vendor", "testdata":
-						return filepath.SkipDir
-					}
+				if !explicit && shouldIgnore(path) {
+					return filepath.SkipDir
 				}
 				return nil // simply recurse into directories
 			case explicit:
@@ -547,6 +544,56 @@ func gofmtMain(s *sequencer) {
 	}
 }
 
+func shouldIgnore(path string) bool {
+	switch filepath.Base(path) {
+	case "vendor", "testdata":
+		return true
+	}
+	path, err := filepath.Abs(path)
+	if err != nil {
+		return false // unclear how this could happen; don't ignore in any case
+	}
+	mod := loadModule(path)
+	if mod == nil {
+		return false // no module file to declare ignore paths
+	}
+	relPath, err := filepath.Rel(mod.absDir, path)
+	if err != nil {
+		return false // unclear how this could happen; don't ignore in any case
+	}
+	relPath = normalizePath(relPath)
+	for _, ignore := range mod.file.Ignore {
+		if matchIgnore(ignore.Path, relPath) {
+			return true
+		}
+	}
+	return false
+}
+
+// normalizePath adds slashes to the front and end of the given path.
+func normalizePath(path string) string {
+	path = filepath.ToSlash(path) // ensure Windows support
+	if !strings.HasPrefix(path, "/") {
+		path = "/" + path
+	}
+	if !strings.HasSuffix(path, "/") {
+		path += "/"
+	}
+	return path
+}
+
+func matchIgnore(ignore, relPath string) bool {
+	ignore, rooted := strings.CutPrefix(ignore, "./")
+	ignore = normalizePath(ignore)
+	// Note that we only match the directory to be ignored itself,
+	// and not any directories underneath it.
+	// This way, using `gofumpt -w ignored` allows `ignored/subdir` to be formatted.
+	if rooted {
+		return relPath == ignore
+	}
+	return strings.HasSuffix(relPath, ignore)
+}
+
 // A nil entry means the directory is not part of a Go module,
 // or a go.mod file was found but it's invalid.
 // A non-nil entry means this directory, or a parent, is in a valid Go module.

testdata/script/ignore.txtar

@@ -31,15 +31,10 @@ testdata${/}foo${/}foo.go
 module${/}ignore${/}dir${/}ignore.go
 -- implicit-dot.stdout --
 ignore${/}dir${/}outsidemodule.go
-module${/}ignore${/}dir${/}ignore.go
-module${/}ignore${/}dir${/}subdir${/}ignore.go
 module${/}ignore${/}dirsuffix${/}nomatch.go
 module${/}ignore${/}nomatch.go
-module${/}ignoreroot${/}dir${/}ignore.go
-module${/}ignoreroot${/}dir${/}subdir${/}ignore.go
 module${/}ignoreroot${/}nomatch.go
 module${/}prefixignore${/}dir${/}nomatch.go
-module${/}subdir${/}ignore${/}dir${/}ignore.go
 module${/}subdir${/}ignoreroot${/}dir${/}notatroot.go
 -- explicit-dirs-unclean.stdout --
 ${WORK}${/}vendor${/}bar${/}bar.go