Fix: check MutuallyExclusiveFlags across parent command chain

command_run.go

@@ -237,14 +237,18 @@ func (cmd *Command) run(ctx context.Context, osArgs []string) (_ context.Context
 		}()
 	}
 
-	for _, grp := range cmd.MutuallyExclusiveFlags {
-		if err := grp.check(cmd); err != nil {
-			if cmd.OnUsageError != nil {
-				err = cmd.OnUsageError(ctx, cmd, err, cmd.parent != nil)
-			} else {
-				_ = ShowSubcommandHelp(cmd)
+	// Walk the parent chain to check mutually exclusive flag groups
+	// defined on ancestor commands, since persistent flags are inherited.
+	for pCmd := cmd; pCmd != nil; pCmd = pCmd.parent {
+		for _, grp := range pCmd.MutuallyExclusiveFlags {
+			if err := grp.check(cmd); err != nil {
+				if cmd.OnUsageError != nil {
+					err = cmd.OnUsageError(ctx, cmd, err, cmd.parent != nil)
+				} else {
+					_ = ShowSubcommandHelp(cmd)
+				}
+				return ctx, err
 			}
-			return ctx, err
 		}
 	}
 

command_test.go

@@ -5445,39 +5445,100 @@ func TestCommand_ParallelRun(t *testing.T) {
 	}
 }
 
-func TestCommand_ExclusiveFlagsPersistentPropagation(t *testing.T) {
-	var subCmdAlphaValue string
+func TestCommand_ExclusiveFlagsPersistent(t *testing.T) {
+	exclusiveGroup := func(flags ...string) []MutuallyExclusiveFlags {
+		grp := MutuallyExclusiveFlags{}
+		for _, name := range flags {
+			grp.Flags = append(grp.Flags, []Flag{&StringFlag{Name: name}})
+		}
+		return []MutuallyExclusiveFlags{grp}
+	}
 
-	cmd := &Command{
-		Name: "root",
-		MutuallyExclusiveFlags: []MutuallyExclusiveFlags{
-			{
-				Flags: [][]Flag{
-					{
-						&StringFlag{
-							Name: "alpha",
-						},
-					},
-					{
-						&StringFlag{
-							Name: "beta",
-						},
-					},
-				},
+	noop := func(_ context.Context, _ *Command) error { return nil }
+
+	newBaseCmd := func() *Command {
+		return &Command{
+			Name:                   "root",
+			MutuallyExclusiveFlags: exclusiveGroup("alpha", "beta"),
+			Commands:               []*Command{{Name: "sub", Action: noop}},
+		}
+	}
+
+	tests := []struct {
+		name    string
+		setup   func() *Command
+		args    []string
+		wantErr string
+	}{
+		{
+			name:  "single flag propagated to subcommand",
+			setup: newBaseCmd,
+			args:  []string{"root", "sub", "--alpha", "hello"},
+		},
+		{
+			name:    "both exclusive flags on subcommand errors",
+			setup:   newBaseCmd,
+			args:    []string{"root", "sub", "--alpha", "hello", "--beta", "world"},
+			wantErr: "cannot be set along with",
+		},
+		{
+			name:  "neither flag set without required is ok",
+			setup: newBaseCmd,
+			args:  []string{"root", "sub"},
+		},
+		{
+			name: "exclusive flags checked on grandchild",
+			setup: func() *Command {
+				cmd := newBaseCmd()
+				sub := cmd.Commands[0]
+				sub.Name = "mid"
+				sub.Action = nil
+				sub.Commands = []*Command{{Name: "leaf", Action: noop}}
+				return cmd
+			},
+			args:    []string{"root", "mid", "leaf", "--alpha", "hello", "--beta", "world"},
+			wantErr: "cannot be set along with",
+		},
+		{
+			name: "subcommand own group checked alongside parent group",
+			setup: func() *Command {
+				cmd := newBaseCmd()
+				cmd.Commands[0].MutuallyExclusiveFlags = exclusiveGroup("gamma", "delta")
+				return cmd
 			},
+			args:    []string{"root", "sub", "--gamma", "hello", "--delta", "world"},
+			wantErr: "cannot be set along with",
 		},
-		Commands: []*Command{
-			{
-				Name: "sub",
-				Action: func(_ context.Context, cmd *Command) error {
-					subCmdAlphaValue = cmd.String("alpha")
-					return nil
-				},
+		{
+			name: "parent group violation detected when subcommand has own group",
+			setup: func() *Command {
+				cmd := newBaseCmd()
+				cmd.Commands[0].MutuallyExclusiveFlags = exclusiveGroup("gamma", "delta")
+				return cmd
+			},
+			args:    []string{"root", "sub", "--alpha", "hello", "--beta", "world"},
+			wantErr: "cannot be set along with",
+		},
+		{
+			name: "parent and subcommand groups both pass independently",
+			setup: func() *Command {
+				cmd := newBaseCmd()
+				cmd.Commands[0].MutuallyExclusiveFlags = exclusiveGroup("gamma", "delta")
+				return cmd
 			},
+			args: []string{"root", "sub", "--alpha", "hello", "--gamma", "world"},
 		},
 	}
 
-	err := cmd.Run(buildTestContext(t), []string{"root", "sub", "--alpha", "hello"})
-	require.NoError(t, err)
-	assert.Equal(t, "hello", subCmdAlphaValue)
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := tt.setup().Run(buildTestContext(t), tt.args)
+			if tt.wantErr != "" {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), tt.wantErr)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
 }