Fix Issue #2385

flag_mutex.go

@@ -17,32 +17,49 @@ type MutuallyExclusiveFlags struct {
 }
 
 func (grp MutuallyExclusiveFlags) check(_ *Command) error {
-	oneSet := false
 	e := &mutuallyExclusiveGroup{}
 
-	for _, grpf := range grp.Flags {
-		for _, f := range grpf {
-			if f.IsSet() {
-				if oneSet {
-					e.flag2Name = f.Names()[0]
-					return e
-				}
-				e.flag1Name = f.Names()[0]
-				oneSet = true
-				break
-			}
-			if oneSet {
-				break
-			}
+	// Check for the use of a mutually-exclusive flag, starting at
+	// the first group.
+	name, i, ok := grp.findSetFlag(0)
+	if ok {
+		e.flag1Name = name
+		i++
+
+		// Check for the use of a flag in a mutually exclusive
+		// relationship with the one we just found.
+		if name2, _, ok := grp.findSetFlag(i); ok {
+			e.flag2Name = name2
+			return e
 		}
 	}
 
-	if !oneSet && grp.Required {
+	if !ok && grp.Required {
 		return &mutuallyExclusiveGroupRequiredFlag{flags: &grp}
 	}
+
 	return nil
 }
 
+// findSetFlag is used in [MutuallyExclusiveFlags.check] to find
+// whether at least one flag inside a mutually exclusive flag group is
+// set. If so, return the flag name, position at which it's set, and
+// Boolean true (indicating that a flag was found.) Else, return all
+// zero values.
+func (grp MutuallyExclusiveFlags) findSetFlag(startIdx int) (string, int, bool) {
+	for i := startIdx; i < len(grp.Flags); i++ {
+		flags := grp.Flags[i]
+
+		for _, flg := range flags {
+			if flg.IsSet() {
+				return flg.Names()[0], i, true
+			}
+		}
+	}
+
+	return "", 0, false
+}
+
 func (grp MutuallyExclusiveFlags) propagateCategory() {
 	for _, grpf := range grp.Flags {
 		for _, f := range grpf {

flag_mutex_test.go

@@ -30,6 +30,9 @@ func newCommand() *Command {
 							Aliases: []string{"ai"},
 							Sources: EnvVars("T_VAR"),
 						},
+						&BoolFlag{
+							Name: "q",
+						},
 					},
 				},
 			},
@@ -73,6 +76,12 @@ func TestFlagMutuallyExclusiveFlags(t *testing.T) {
 			errStr:   "option i cannot be set along with option ai",
 			required: true,
 		},
+		{
+			name:     "required both set second member",
+			args:     []string{"--i", "11", "--q"},
+			errStr:   "option i cannot be set along with option q",
+			required: true,
+		},
 		{
 			name:     "set env var",
 			required: true,