cli: search for the tree root by default

Restore the treefmt 1.x behaviour where it would search for the tree
root by recursively searching for the treefmt.toml file up the
filesystem, starting from the current directory.

The `--tree-root-file` option will be useful to remove this bash wrapper: https://github.com/numtide/treefmt-nix/blob/2fba33a182602b9d49f0b2440513e5ee091d838b/module-options.nix#L116-L135

Fixes #308

cli/cli.go

@@ -13,10 +13,11 @@ type Format struct {
 	WorkingDirectory      kong.ChangeDirFlag `default:"." short:"C" help:"Run as if treefmt was started in the specified working directory instead of the current working directory."`
 	NoCache               bool               `help:"Ignore the evaluation cache entirely. Useful for CI."`
 	ClearCache            bool               `short:"c" help:"Reset the evaluation cache. Use in case the cache is not precise enough."`
-	ConfigFile            string             `type:"existingfile" default:"./treefmt.toml" help:"The config file to use."`
+	ConfigFile            string             `type:"path" help:"Load the config file from the given path (defaults to finding treefmt.toml up)."`
 	FailOnChange          bool               `help:"Exit with error if any changes were made. Useful for CI."`
 	Formatters            []string           `short:"f" help:"Specify formatters to apply. Defaults to all formatters."`
-	TreeRoot              string             `type:"existingdir" default:"." help:"The root directory from which treefmt will start walking the filesystem."`
+	TreeRoot              string             `type:"path" help:"The root directory from which treefmt will start walking the filesystem (defaults to the directory containing the config file)."`
+	TreeRootFile          string             `type:"path" help:"File to search for to find the project root (if --tree-root is not passed)."`
 	Walk                  walk.Type          `enum:"auto,git,filesystem" default:"auto" help:"The method used to traverse the files within --tree-root. Currently supports 'auto', 'git' or 'filesystem'."`
 	Verbosity             int                `name:"verbose" short:"v" type:"counter" default:"0" env:"LOG_LEVEL" help:"Set the verbosity of logs e.g. -vv."`
 	Version               bool               `name:"version" short:"V" help:"Print version."`

cli/format.go

@@ -69,6 +69,40 @@ func (f *Format) Run() (err error) {
 		}
 	}()
 
+	// find the config file unless specified
+	if Cli.ConfigFile == "" {
+		pwd, err := os.Getwd()
+		if err != nil {
+			return err
+		}
+		Cli.ConfigFile, _, err = findUp(pwd, "treefmt.toml")
+		if err != nil {
+			return err
+		}
+	}
+
+	// search for the project root unless specified
+	if Cli.TreeRoot == "" {
+		// use the location of the treefmt.toml file by default
+		dir := filepath.Dir(Cli.ConfigFile)
+
+		// search using the --tree-root-file if specified
+		if Cli.TreeRootFile != "" {
+			pwd, err := os.Getwd()
+			if err != nil {
+				return err
+			}
+			_, dir, err = findUp(pwd, Cli.TreeRootFile)
+			if err != nil {
+				return err
+			}
+		}
+
+		Cli.TreeRoot = dir
+	}
+
+	log.Debugf("config-file=%s tree-root=%s", Cli.ConfigFile, Cli.TreeRoot)
+
 	// read config
 	cfg, err := config.ReadFile(Cli.ConfigFile, Cli.Formatters)
 	if err != nil {
@@ -384,3 +418,56 @@ func applyFormatters(ctx context.Context) func() error {
 		return nil
 	}
 }
+
+func findUp(searchDir string, fileName string) (path string, dir string, err error) {
+	for _, dir := range eachDir(searchDir) {
+		path := filepath.Join(dir, fileName)
+		if fileExists(path) {
+			return path, dir, nil
+		}
+	}
+	return "", "", fmt.Errorf("could not find %s in %s", fileName, searchDir)
+}
+
+func eachDir(path string) (paths []string) {
+	path, err := filepath.Abs(path)
+	if err != nil {
+		return
+	}
+
+	paths = []string{path}
+
+	if path == "/" {
+		return
+	}
+
+	for i := len(path) - 1; i >= 0; i-- {
+		if path[i] == os.PathSeparator {
+			path = path[:i]
+			if path == "" {
+				path = "/"
+			}
+			paths = append(paths, path)
+		}
+	}
+
+	return
+}
+
+func fileExists(path string) bool {
+	// Some broken filesystems like SSHFS return file information on stat() but
+	// then cannot open the file. So we use os.Open.
+	f, err := os.Open(path)
+	if err != nil {
+		return false
+	}
+	defer f.Close()
+
+	// Next, check that the file is a regular file.
+	fi, err := f.Stat()
+	if err != nil {
+		return false
+	}
+
+	return fi.Mode().IsRegular()
+}