watchpr: reject --max-wait with --once, test exit-code mapping

cmd/watchpr/main.go

@@ -47,12 +47,18 @@ var errTimedOut = errors.New("max-wait elapsed with no change")
 func main() {
 	// cobra prints the error itself (SilenceErrors stays off); we only need to
 	// turn any command error into a non-zero exit.
-	if err := newRootCmd().Execute(); err != nil {
-		if errors.Is(err, errTimedOut) {
-			os.Exit(exitTimedOut)
-		}
-		os.Exit(1)
+	os.Exit(exitCode(newRootCmd().Execute()))
+}
+
+// exitCode maps a command result to the process exit status.
+func exitCode(err error) int {
+	switch {
+	case err == nil:
+		return 0
+	case errors.Is(err, errTimedOut):
+		return exitTimedOut
 	}
+	return 1
 }
 
 // newRootCmd builds the watchpr command tree. It is separated from main so
@@ -86,6 +92,9 @@ func newRootCmd() *cobra.Command {
 			if err != nil {
 				return err
 			}
+			if once && maxWait > 0 {
+				return fmt.Errorf("--max-wait has no effect with --once")
+			}
 			refs := make([]agent.PRRef, 0, len(args))
 			for _, a := range args {
 				ref, err := agent.ParsePRRef(a)

cmd/watchpr/main_test.go

@@ -336,6 +336,36 @@ func TestExecuteBadMaxWaitErrors(t *testing.T) {
 	}
 }
 
+func TestExecuteOnceWithMaxWaitErrors(t *testing.T) {
+	cmd := newRootCmd()
+	cmd.SetArgs([]string{"--once", "--max-wait", "5m", "unkin/repo#1"})
+	cmd.SetOut(io.Discard)
+	cmd.SetErr(io.Discard)
+	err := cmd.Execute()
+	if err == nil || !strings.Contains(err.Error(), "--once") {
+		t.Fatalf("Execute() = %v, want a --once/--max-wait conflict error", err)
+	}
+	if got := exitCode(err); got != 1 {
+		t.Fatalf("exitCode = %d, want 1", got)
+	}
+}
+
+func TestExitCode(t *testing.T) {
+	for _, tc := range []struct {
+		err  error
+		want int
+	}{
+		{nil, 0},
+		{errTimedOut, exitTimedOut},
+		{fmt.Errorf("wrapped: %w", errTimedOut), exitTimedOut},
+		{errors.New("boom"), 1},
+	} {
+		if got := exitCode(tc.err); got != tc.want {
+			t.Errorf("exitCode(%v) = %d, want %d", tc.err, got, tc.want)
+		}
+	}
+}
+
 // Ticks pass through until the deadline fires; then the channel closes without
 // waiting for another tick.
 func TestUntilDeadline(t *testing.T) {