cmd/cue: fix help cmd incorrect behavior

cmd/cue/cmd/help.go

@@ -15,9 +15,14 @@
 package cmd
 
 import (
+	"os"
+	"strings"
+
 	"github.com/spf13/cobra"
 )
 
+var osExit = os.Exit
+
 // TODO: intersperse the examples at the end of the texts in the
 // body of text to make things more concrete for the user early on?
 // The current approach works will if users just print the text without
@@ -34,7 +39,7 @@ func newHelpCmd(c *Command) *cobra.Command {
 		Long: `Help provides help for any command in the application.
 Simply type ` + c.Name() + ` help [path to command] for full details.`,
 		Run: func(_ *cobra.Command, args []string) {
-			cmd, _, e := c.Root().Find(args)
+			cmd, rests, e := c.Root().Find(args)
 			if len(args) > 0 && args[0] == "cmd" {
 				// args is one of:
 				//
@@ -52,15 +57,15 @@ Simply type ` + c.Name() + ` help [path to command] for full details.`,
 				if err == nil {
 					addCustomCommands(c, cmd, commandSection, tools)
 					// For the sake of `cue help cmd mycmd`, find the command again.
-					cmd, _, e = c.Root().Find(args)
+					cmd, rests, e = c.Root().Find(args)
 				}
 			}
-			if cmd == nil || e != nil {
-				c.Printf("Unknown help topic %#q\n", args)
-				cobra.CheckErr(c.Root().Usage())
-			} else {
-				cobra.CheckErr(cmd.Help())
+			// If rests are not empty, args are invalid.
+			if cmd == nil || e != nil || len(rests) != 0 {
+				c.PrintErrf("Unknown help command: %#q\n", strings.Join(args, " "))
+				osExit(1)
 			}
+			cobra.CheckErr(cmd.Help())
 		},
 	}
 	return cmd

cmd/cue/cmd/root_test.go

@@ -59,4 +59,25 @@ func TestHelp(t *testing.T) {
 	if err := run("eval", "--help"); err != nil {
 		t.Error("help command failed unexpectedly")
 	}
+
+	// os.Exit(1) is expected
+	testOsExit(t, 1, []string{"help", "foo"}, run)
+
+	testOsExit(t, 1, []string{"help", "cmd", "foo"}, run)
+}
+
+// testOsExit tests that os.Exit is called with the given code when running f.
+func testOsExit(t *testing.T, code int, args []string, f func(args ...string) error) {
+	t.Helper()
+	oldExit := osExit
+	defer func() { osExit = oldExit }()
+	var status int
+	exit := func(code int) {
+		status = code
+	}
+	osExit = exit
+	f(args...)
+	if status != code {
+		t.Errorf("os.Exit(%d) not called", code)
+	}
 }