feat: add notify based formatter

cmd/format/format.go

@@ -167,6 +167,7 @@ func Run(v *viper.Viper, statz *stats.Stats, cmd *cobra.Command, paths []string)
 	// start traversing
 	files := make([]*walk.File, BatchSize)
 
+LOOP:
 	for {
 		// read the next batch
 		readCtx, cancel := context.WithTimeout(ctx, 1*time.Second)
@@ -180,17 +181,21 @@ func Run(v *viper.Viper, statz *stats.Stats, cmd *cobra.Command, paths []string)
 			return fmt.Errorf("formatting failure: %w", err)
 		}
 
-		if errors.Is(err, io.EOF) {
+		switch {
+		case errors.Is(err, io.EOF):
 			// we have finished traversing
-			break
-		} else if err != nil {
+			break LOOP
+		case cfg.Watch && errors.Is(err, context.DeadlineExceeded):
+			// we timed out reading files, try again
+			continue
+		case err != nil:
 			// something went wrong
 			return fmt.Errorf("failed to read files: %w", err)
 		}
 	}
 
 	// finalize formatting
-	formatErr := formatter.Close(ctx)
+	formatErr := formatter.Close()
 
 	// close the walker, ensuring any pending file release hooks finish
 	if err = walker.Close(); err != nil {

config/config.go

@@ -29,6 +29,7 @@ type Config struct {
 	Walk                  string   `mapstructure:"walk"                    toml:"walk,omitempty"`
 	WorkingDirectory      string   `mapstructure:"working-dir"             toml:"-"`
 	Stdin                 bool     `mapstructure:"stdin"                   toml:"-"` // not allowed in config
+	Watch                 bool     `mapstructure:"watch"                   toml:"-"` // not allowed in config
 
 	FormatterConfigs map[string]*Formatter `mapstructure:"formatter" toml:"formatter,omitempty"`
 
@@ -98,6 +99,10 @@ func SetFlags(fs *pflag.FlagSet) {
 		"stdin", false,
 		"Format the context passed in via stdin.",
 	)
+	fs.Bool(
+		"watch", false,
+		"Watch the filesystem for changes and apply formatters when changes are detected. (env $TREEFMT_WATCH)",
+	)
 	fs.String(
 		"tree-root", "",
 		"The root directory from which treefmt will start walking the filesystem (defaults to the directory "+
@@ -157,6 +162,7 @@ func FromViper(v *viper.Viper) (*Config, error) {
 		"clear-cache": false,
 		"no-cache":    false,
 		"stdin":       false,
+		"watch":       false,
 		"working-dir": ".",
 	}
 
@@ -185,6 +191,11 @@ func FromViper(v *viper.Viper) (*Config, error) {
 		cfg.Walk = walk.Stdin.String()
 	}
 
+	// if the watch flag was passed, we force the watch walk type
+	if cfg.Watch {
+		cfg.Walk = walk.Watch.String()
+	}
+
 	// determine the tree root
 	if cfg.TreeRoot == "" {
 		// if none was specified, we first try with tree-root-file

format/composite.go

@@ -107,6 +107,8 @@ func (c *CompositeFormatter) Apply(ctx context.Context, files []*walk.File) erro
 		}
 	}
 
+	c.scheduler.apply(ctx)
+
 	return nil
 }
 
@@ -136,8 +138,8 @@ func (c *CompositeFormatter) signature() (signature, error) {
 
 // Close finalizes the processing of the CompositeFormatter, ensuring that any remaining batches are applied and
 // all formatters have completed their tasks. It returns an error if any formatting failures were detected.
-func (c *CompositeFormatter) Close(ctx context.Context) error {
-	return c.scheduler.close(ctx)
+func (c *CompositeFormatter) Close() error {
+	return c.scheduler.close()
 }
 
 func NewCompositeFormatter(

format/scheduler.go

@@ -203,14 +203,16 @@ func (s *scheduler) schedule(ctx context.Context, key batchKey, batch []*walk.Fi
 	})
 }
 
-func (s *scheduler) close(ctx context.Context) error {
+func (s *scheduler) apply(ctx context.Context) {
 	// schedule any partial batches that remain
 	for key, batch := range s.batches {
 		if len(batch) > 0 {
 			s.schedule(ctx, key, batch)
 		}
 	}
+}
 
+func (s *scheduler) close() error {
 	// wait for processing to complete
 	if err := s.eg.Wait(); err != nil {
 		return fmt.Errorf("failed to wait for formatters: %w", err)

test/test.go

@@ -14,6 +14,43 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+//nolint:gochecknoglobals
+var ExamplesPaths = []string{
+	"elm/elm.json",
+	"elm/src/Main.elm",
+	"emoji 🕰️/README.md",
+	"go/go.mod",
+	"go/main.go",
+	"haskell/CHANGELOG.md",
+	"haskell/Foo.hs",
+	"haskell/Main.hs",
+	"haskell/Nested/Foo.hs",
+	"haskell/Setup.hs",
+	"haskell/haskell.cabal",
+	"haskell/treefmt.toml",
+	"haskell-frontend/CHANGELOG.md",
+	"haskell-frontend/Main.hs",
+	"haskell-frontend/Setup.hs",
+	"haskell-frontend/haskell-frontend.cabal",
+	"html/index.html",
+	"html/scripts/.gitkeep",
+	"javascript/source/hello.js",
+	"nix/sources.nix",
+	"nixpkgs.toml",
+	"python/main.py",
+	"python/requirements.txt",
+	"python/virtualenv_proxy.py",
+	"ruby/bundler.rb",
+	"rust/Cargo.toml",
+	"rust/src/main.rs",
+	"shell/foo.sh",
+	"terraform/main.tf",
+	"terraform/two.tf",
+	"touch.toml",
+	"treefmt.toml",
+	"yaml/test.yaml",
+}
+
 func WriteConfig(t *testing.T, path string, cfg *config.Config) {
 	t.Helper()
 

walk/filesystem_test.go

@@ -13,43 +13,6 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-//nolint:gochecknoglobals
-var examplesPaths = []string{
-	"elm/elm.json",
-	"elm/src/Main.elm",
-	"emoji 🕰️/README.md",
-	"go/go.mod",
-	"go/main.go",
-	"haskell/CHANGELOG.md",
-	"haskell/Foo.hs",
-	"haskell/Main.hs",
-	"haskell/Nested/Foo.hs",
-	"haskell/Setup.hs",
-	"haskell/haskell.cabal",
-	"haskell/treefmt.toml",
-	"haskell-frontend/CHANGELOG.md",
-	"haskell-frontend/Main.hs",
-	"haskell-frontend/Setup.hs",
-	"haskell-frontend/haskell-frontend.cabal",
-	"html/index.html",
-	"html/scripts/.gitkeep",
-	"javascript/source/hello.js",
-	"nix/sources.nix",
-	"nixpkgs.toml",
-	"python/main.py",
-	"python/requirements.txt",
-	"python/virtualenv_proxy.py",
-	"ruby/bundler.rb",
-	"rust/Cargo.toml",
-	"rust/src/main.rs",
-	"shell/foo.sh",
-	"terraform/main.tf",
-	"terraform/two.tf",
-	"touch.toml",
-	"treefmt.toml",
-	"yaml/test.yaml",
-}
-
 func TestFilesystemReader(t *testing.T) {
 	as := require.New(t)
 
@@ -67,7 +30,7 @@ func TestFilesystemReader(t *testing.T) {
 		n, err := r.Read(ctx, files)
 
 		for i := count; i < count+n; i++ {
-			as.Equal(examplesPaths[i], files[i-count].RelPath)
+			as.Equal(test.ExamplesPaths[i], files[i-count].RelPath)
 		}
 
 		count += n

walk/walk.go

@@ -22,6 +22,7 @@ const (
 	Stdin
 	Filesystem
 	Git
+	Watch
 
 	BatchSize = 1024
 )
@@ -215,6 +216,8 @@ func NewReader(
 		reader = NewFilesystemReader(root, path, statz, BatchSize)
 	case Git:
 		reader, err = NewGitReader(root, path, statz)
+	case Watch:
+		reader, err = NewWatchReader(root, path, statz, BatchSize)
 
 	default:
 		return nil, fmt.Errorf("unknown walk type: %v", walkType)