fix: change flag parse error handling to return errors instead of exi…

…ting (#107)

* fix: change flag parse error handling to return errors instead of exiting

Having ExitOnError in combination with SetOutput to a buffer instead of
stdout/stderr means flags.Parse output is swallowed and kubeconform silently
exits directly with exit code 2 instead of returning the error.

Setting ContinueOnError instead returns the error, and writes usage help to
the buffer, so error handling code in main is reached.

* Add test for parsing incorrect flags

Co-authored-by: Yann Hamon <yann@mandragor.org>

acceptance.bats

@@ -11,6 +11,12 @@ resetCacheFolder() {
   [ "${lines[0]}" == 'Usage: bin/kubeconform [OPTION]... [FILE OR FOLDER]...' ]
 }
 
+@test "Fail and display help when using an incorrect flag" {
+  run bin/kubeconform -xyz
+  [ "$status" -eq 1 ]
+  [ "${lines[0]}" == 'flag provided but not defined: -xyz' ]
+}
+
 @test "Pass when parsing a valid Kubernetes config YAML file" {
   run bin/kubeconform -summary fixtures/valid.yaml
   [ "$status" -eq 0 ]

pkg/config/config.go

@@ -56,7 +56,7 @@ func splitCSV(csvStr string) map[string]struct{} {
 func FromFlags(progName string, args []string) (Config, string, error) {
 	var schemaLocationsParam, ignoreFilenamePatterns arrayParam
 	var skipKindsCSV, rejectKindsCSV string
-	flags := flag.NewFlagSet(progName, flag.ExitOnError)
+	flags := flag.NewFlagSet(progName, flag.ContinueOnError)
 	var buf bytes.Buffer
 	flags.SetOutput(&buf)