cmd: `caddy fmt` return code is 1 if not formatted (#5297)

* cmd: Fix caddy fmt if input isn't formatted

* Fixes #5294
* return exit 1 with an error message

* cmd: Use formattingDifference for caddy fmt

* #5294
* expose caddyfile.formattingDifference

2 files changed, 7 insertions, 3 deletions

diff --git a/caddyconfig/caddyfile/adapter.go b/caddyconfig/caddyfile/adapter.go
index d5bb7c2..b924325 100644
--- a/caddyconfig/caddyfile/adapter.go
+++ b/caddyconfig/caddyfile/adapter.go
@@ -54,7 +54,7 @@ func (a Adapter) Adapt(body []byte, options map[string]any) ([]byte, []caddyconf
 
 	// lint check: see if input was properly formatted; sometimes messy files files parse
 	// successfully but result in logical errors (the Caddyfile is a bad format, I'm sorry)
-	if warning, different := formattingDifference(filename, body); different {
+	if warning, different := FormattingDifference(filename, body); different {
 		warnings = append(warnings, warning)
 	}
 
@@ -63,10 +63,10 @@ func (a Adapter) Adapt(body []byte, options map[string]any) ([]byte, []caddyconf
 	return result, warnings, err
 }
 
-// formattingDifference returns a warning and true if the formatted version
+// FormattingDifference returns a warning and true if the formatted version
 // is any different from the input; empty warning and false otherwise.
 // TODO: also perform this check on imported files
-func formattingDifference(filename string, body []byte) (caddyconfig.Warning, bool) {
+func FormattingDifference(filename string, body []byte) (caddyconfig.Warning, bool) {
 	// replace windows-style newlines to normalize comparison
 	normalizedBody := bytes.Replace(body, []byte("\r\n"), []byte("\n"), -1)
 
diff --git a/cmd/commandfuncs.go b/cmd/commandfuncs.go
index e3daae5..bc4c227 100644
--- a/cmd/commandfuncs.go
+++ b/cmd/commandfuncs.go
@@ -576,6 +576,10 @@ func cmdFmt(fl Flags) (int, error) {
 		fmt.Print(string(output))
 	}
 
+	if warning, diff := caddyfile.FormattingDifference(formatCmdConfigFile, input); diff {
+		return caddy.ExitCodeFailedStartup, fmt.Errorf("%s:%d: Caddyfile input is not formatted", warning.File, warning.Line)
+	}
+
 	return caddy.ExitCodeSuccess, nil
 }