#2396: Add cobra unique args validator

args.go

@@ -65,6 +65,19 @@ func OnlyValidArgs(cmd *Command, args []string) error {
 	return nil
 }
 
+// NoDuplicateArgs returns an error if there are any duplicate positional args.
+func NoDuplicateArgs(cmd *Command, args []string) error {
+	seen := make(map[string]struct{}, len(args))
+	for _, arg := range args {
+		if _, ok := seen[arg]; ok {
+			return fmt.Errorf("duplicate argument %q for %q", arg, cmd.CommandPath())
+		}
+		seen[arg] = struct{}{}
+	}
+
+	return nil
+}
+
 // ArbitraryArgs never returns an error.
 func ArbitraryArgs(cmd *Command, args []string) error {
 	return nil

args_test.go

@@ -107,6 +107,17 @@ func rangeArgsWithInvalidCount(err error, t *testing.T) {
 	}
 }
 
+func noDuplicateArgsWithDuplicate(err error, t *testing.T, arg string) {
+	if err == nil {
+		t.Fatal("Expected an error")
+	}
+	got := err.Error()
+	expected := `duplicate argument "` + arg + `" for "c"`
+	if got != expected {
+		t.Errorf("Expected: %q, got: %q", expected, got)
+	}
+}
+
 // NoArgs
 
 func TestNoArgs(t *testing.T) {
@@ -153,6 +164,32 @@ func TestOnlyValidArgs_WithInvalidArgs(t *testing.T) {
 	validOnlyWithInvalidArgs(err, t)
 }
 
+// NoDuplicateArgs
+
+func TestNoDuplicateArgs(t *testing.T) {
+	c := getCommand(NoDuplicateArgs, false)
+	output, err := executeCommand(c, "one", "two")
+	expectSuccess(output, err, t)
+}
+
+func TestNoDuplicateArgs_WithDuplicateArgs(t *testing.T) {
+	c := getCommand(NoDuplicateArgs, false)
+	_, err := executeCommand(c, "one", "one")
+	noDuplicateArgsWithDuplicate(err, t, "one")
+}
+
+func TestNoDuplicateArgs_WithValid_WithDuplicateArgs(t *testing.T) {
+	c := getCommand(NoDuplicateArgs, true)
+	_, err := executeCommand(c, "one", "one")
+	noDuplicateArgsWithDuplicate(err, t, "one")
+}
+
+func TestNoDuplicateArgs_WithValidOnly_WithInvalidArgs(t *testing.T) {
+	c := getCommand(MatchAll(OnlyValidArgs, NoDuplicateArgs), true)
+	_, err := executeCommand(c, "a", "a")
+	validOnlyWithInvalidArgs(err, t)
+}
+
 // ArbitraryArgs
 
 func TestArbitraryArgs(t *testing.T) {

site/content/user_guide.md

@@ -447,6 +447,7 @@ The following validators are built in:
   - `RangeArgs(min, max)` - report an error if the number of args is not between `min` and `max`.
 - Content of the arguments:
   - `OnlyValidArgs` - report an error if there are any positional args not specified in the `ValidArgs` field of `Command`, which can optionally be set to a list of valid values for positional args.
+  - `NoDuplicateArgs` - report an error if any positional argument value is provided more than once.
 
 If `Args` is undefined or `nil`, it defaults to `ArbitraryArgs`.