feat: support fail on change (#16)

Closes #8

Signed-off-by: Brian McGee <brian@bmcgee.ie>

Reviewed-on: #16
Reviewed-by: Jonas Chevalier <zimbatm@noreply.git.numtide.com>
Co-authored-by: Brian McGee <brian@bmcgee.ie>
Co-committed-by: Brian McGee <brian@bmcgee.ie>

internal/cli/cli.go

@@ -10,6 +10,7 @@ type Options struct {
 	AllowMissingFormatter bool     `default:"false" help:"Do not exit with error if a configured formatter is missing"`
 	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"`
+	FailOnChange          bool     `help:"Exit with error if any changes were made. Useful for CI"`
 	Formatters            []string `help:"Specify formatters to apply. Defaults to all formatters"`
 	TreeRoot              string   `type:"existingdir" default:"."`
 	Verbosity             int      `name:"verbose" short:"v" type:"counter" default:"0" env:"LOG_LEVEL" help:"Set the verbosity of logs e.g. -vv"`

internal/cli/format.go

@@ -18,6 +18,8 @@ import (
 
 type Format struct{}
 
+var ErrFailOnChange = errors.New("unexpected changes detected, --fail-on-change is enabled")
+
 func (f *Format) Run() error {
 	start := time.Now()
 
@@ -155,6 +157,10 @@ func (f *Format) Run() error {
 		}
 		changes += count
 
+		if Cli.FailOnChange && changes != 0 {
+			return ErrFailOnChange
+		}
+
 		fmt.Printf("%v files changed in %v", changes, time.Now().Sub(start))
 		return nil
 	})

internal/cli/format_test.go

@@ -179,6 +179,27 @@ func TestCache(t *testing.T) {
 	as.Contains(string(out), "0 files changed")
 }
 
+func TestFailOnChange(t *testing.T) {
+	as := require.New(t)
+
+	tempDir := test.TempExamples(t)
+	configPath := tempDir + "/echo.toml"
+
+	// test without any excludes
+	config := format.Config{
+		Formatters: map[string]*format.Formatter{
+			"echo": {
+				Command:  "echo",
+				Includes: []string{"*"},
+			},
+		},
+	}
+
+	test.WriteConfig(t, configPath, config)
+	_, err := cmd(t, "--fail-on-change", "--config-file", configPath, "--tree-root", tempDir)
+	as.ErrorIs(err, ErrFailOnChange)
+}
+
 func TestBustCacheOnFormatterChange(t *testing.T) {
 	as := require.New(t)