fly: print help for subcommands

still print it on stdout and still return 0 status code.

concourse/concourse#4134

Signed-off-by: Jamie Klassen <cklassen@pivotal.io>

fly/integration/help_test.go

@@ -43,4 +43,17 @@ var _ = Describe("Fly CLI", func() {
 			Expect(sess.Out).To(gbytes.Say("Available commands:"))
 		})
 	})
+
+	Context("when invoking a subcommand with -h flag", func() {
+		It("prints help for the given subcommand", func() {
+			flyCmd := exec.Command(flyPath, "completion", "-h")
+
+			sess, err := gexec.Start(flyCmd, GinkgoWriter, GinkgoWriter)
+			Expect(err).NotTo(HaveOccurred())
+
+			<-sess.Exited
+			Expect(sess.ExitCode()).To(Equal(0))
+			Expect(sess.Out).To(gbytes.Say("completion command options"))
+		})
+	})
 })

fly/main.go

@@ -68,7 +68,8 @@ func handleError(helpParser *flags.Parser, err error) {
 		} else if flagsErr, ok := err.(*flags.Error); ok && flagsErr.Type == flags.ErrCommandRequired {
 			showHelp(helpParser)
 		} else if flagsErr, ok := err.(*flags.Error); ok && flagsErr.Type == flags.ErrHelp {
-			showHelp(helpParser)
+			fmt.Println(err)
+			os.Exit(0)
 		} else {
 			fmt.Fprintf(ui.Stderr, "error: %s\n", err)
 		}