Add custom helptext when --json is used

internal/cli/pr.go

@@ -45,13 +45,26 @@ func prViewCmd() *cobra.Command {
 	var (
 		flagComments bool
 		flagWeb      bool
+		flagJSON     string
 	)
 
 	cmd := &cobra.Command{
 		Use:   "view <number>",
 		Short: "View a pull request",
 		Args:  cobra.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
+			if cmd.Flags().Changed("json") {
+				var hints []string
+				hints = append(hints, "forge --output json pr view <number>")
+				if strings.Contains(flagJSON, "comments") {
+					hints = append(hints, "forge pr view --comments <number>")
+				}
+				if strings.Contains(flagJSON, "reviews") {
+					hints = append(hints, "forge pr review list <number>")
+				}
+				return fmt.Errorf("--json is not supported; use --output json instead (field selection is not supported)\n\nTry: %s", strings.Join(hints, "\n     "))
+			}
+
 			number, err := strconv.Atoi(args[0])
 			if err != nil {
 				return fmt.Errorf("invalid PR number: %s", args[0])
@@ -96,6 +109,9 @@ func prViewCmd() *cobra.Command {
 
 	cmd.Flags().BoolVarP(&flagComments, "comments", "c", false, "Show comments")
 	cmd.Flags().BoolVarP(&flagWeb, "web", "w", false, "Open in browser")
+	cmd.Flags().StringVar(&flagJSON, "json", "", "Not supported; use --output json")
+	cmd.Flags().Lookup("json").NoOptDefVal = " "
+	_ = cmd.Flags().MarkHidden("json")
 	return cmd
 }
 

internal/cli/pr_test.go

@@ -142,3 +142,49 @@ func TestPRDiffRequiresArg(t *testing.T) {
 		t.Fatal("expected error for missing argument")
 	}
 }
+
+func TestPRViewJSONFlagNotSupported(t *testing.T) {
+	tests := []struct {
+		name string
+		args []string
+		want string
+	}{
+		{
+			name: "generic field",
+			args: []string{"pr", "view", "--json=title", "1"},
+			want: "--json is not supported; use --output json instead (field selection is not supported)\n\nTry: forge --output json pr view <number>",
+		},
+		{
+			name: "comments field",
+			args: []string{"pr", "view", "--json=comments", "1"},
+			want: "--json is not supported; use --output json instead (field selection is not supported)\n\nTry: forge --output json pr view <number>\n     forge pr view --comments <number>",
+		},
+		{
+			name: "reviews field",
+			args: []string{"pr", "view", "--json=reviews", "1"},
+			want: "--json is not supported; use --output json instead (field selection is not supported)\n\nTry: forge --output json pr view <number>\n     forge pr review list <number>",
+		},
+		{
+			name: "both fields",
+			args: []string{"pr", "view", "--json=reviews,comments", "1"},
+			want: "--json is not supported; use --output json instead (field selection is not supported)\n\nTry: forge --output json pr view <number>\n     forge pr view --comments <number>\n     forge pr review list <number>",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf bytes.Buffer
+			rootCmd.SetOut(&buf)
+			rootCmd.SetErr(&buf)
+			rootCmd.SetArgs(tt.args)
+
+			err := rootCmd.Execute()
+			if err == nil {
+				t.Fatal("expected error for --json flag")
+			}
+			if err.Error() != tt.want {
+				t.Errorf("unexpected error:\ngot:  %s\nwant: %s", err.Error(), tt.want)
+			}
+		})
+	}
+}