feat: ability to exit zero with no releases match selector (#618)

- Change exit code from 2 to 3 when helmfiles have no releases that match a selector
- Introduces new flag `--allow-no-matching-release` to exit 0 when no releases match a selector.

Resolves: #597

cmd/cmd.go

@@ -27,7 +27,7 @@ func VisitAllDesiredStates(c *cli.Context, converge func(*state.HelmState, helme
 
 	err = a.VisitDesiredStates(fileOrDir, a.Selectors, convergeWithHelmBinary)
 
-	return toCliError(err)
+	return toCliError(c, err)
 }
 
 func InitAppEntry(c *cli.Context, reverse bool) (*app.App, string, error) {
@@ -76,14 +76,18 @@ func FindAndIterateOverDesiredStatesUsingFlagsWithReverse(c *cli.Context, revers
 
 	err = a.VisitDesiredStatesWithReleasesFiltered(fileOrDir, convergeWithHelmBinary)
 
-	return toCliError(err)
+	return toCliError(c, err)
 }
 
-func toCliError(err error) error {
+func toCliError(c *cli.Context, err error) error {
 	if err != nil {
 		switch e := err.(type) {
 		case *app.NoMatchingHelmfileError:
-			return cli.NewExitError(e.Error(), 2)
+			noMatchingExitCode := 3
+			if c.GlobalBool("allow-no-matching-release") {
+				noMatchingExitCode = 0
+			}
+			return cli.NewExitError(e.Error(), noMatchingExitCode)
 		case *app.Error:
 			return cli.NewExitError(e.Error(), e.Code())
 		default:

main.go

@@ -82,6 +82,10 @@ func main() {
 	--selector tier=frontend,tier!=proxy --selector tier=backend. Will match all frontend, non-proxy releases AND all backend releases.
 	The name of a release can be used as a label. --selector name=myrelease`,
 		},
+		cli.BoolFlag{
+			Name:  "allow-no-matching-release",
+			Usage: `Do not exit with an error code if the provided selector has no matching releases.`,
+		},
 		cli.BoolFlag{
 			Name:  "interactive, i",
 			Usage: "Request confirmation before attempting to modify clusters",