fix: prevent panic in unique validation with nil pointer elements (#1532)

## Fixes Or Enhances

This is an alternative approach to resolve the panic issue in the unique
validator.
Releated to: #1530

**Make sure that you've checked the boxes below before you submit PR:**
- [ ] Tests exist or have been written that cover this particular
change.

@go-playground/validator-maintainers

Author: nodivbyzero

baked_in.go

@@ -336,61 +336,110 @@ func isOneOfCI(fl FieldLevel) bool {
 func isUnique(fl FieldLevel) bool {
 	field := fl.Field()
 	param := fl.Param()
-	v := reflect.ValueOf(struct{}{})
+
+	// sentinel used as map key for nil values
+	var nilKey = struct{}{}
 
 	switch field.Kind() {
 	case reflect.Slice, reflect.Array:
-		elem := field.Type().Elem()
-		if elem.Kind() == reflect.Ptr {
-			elem = elem.Elem()
-		}
+		seen := make(map[interface{}]struct{})
 
-		if param == "" {
-			m := reflect.MakeMap(reflect.MapOf(elem, v.Type()))
+		for i := 0; i < field.Len(); i++ {
+			elem := field.Index(i)
+
+			// -------- unique (no param) --------
+			if param == "" {
+				var key interface{}
+
+				if elem.Kind() == reflect.Ptr {
+					if elem.IsNil() {
+						key = nilKey
+					} else {
+						key = elem.Elem().Interface() // <-- compare underlying value
+					}
+				} else {
+					key = elem.Interface()
+				}
 
-			for i := 0; i < field.Len(); i++ {
-				m.SetMapIndex(reflect.Indirect(field.Index(i)), v)
+				if _, ok := seen[key]; ok {
+					return false
+				}
+				seen[key] = struct{}{}
+				continue
 			}
-			return field.Len() == m.Len()
-		}
 
-		sf, ok := elem.FieldByName(param)
-		if !ok {
-			panic(fmt.Sprintf("Bad field name %s", param))
-		}
+			// -------- unique=Field --------
 
-		sfTyp := sf.Type
-		if sfTyp.Kind() == reflect.Ptr {
-			sfTyp = sfTyp.Elem()
-		}
+			if elem.Kind() == reflect.Ptr {
+				if elem.IsNil() {
+					if _, ok := seen[nilKey]; ok {
+						return false
+					}
+					seen[nilKey] = struct{}{}
+					continue
+				}
+				elem = elem.Elem()
+			}
 
-		m := reflect.MakeMap(reflect.MapOf(sfTyp, v.Type()))
-		var fieldlen int
-		for i := 0; i < field.Len(); i++ {
-			key := reflect.Indirect(reflect.Indirect(field.Index(i)).FieldByName(param))
-			if key.IsValid() {
-				fieldlen++
-				m.SetMapIndex(key, v)
+			if elem.Kind() != reflect.Struct {
+				panic(fmt.Sprintf("Bad field type %s", elem.Type()))
+			}
+
+			sf := elem.FieldByName(param)
+			if !sf.IsValid() {
+				panic(fmt.Sprintf("Bad field name %s", param))
+			}
+
+			var key interface{}
+
+			if sf.Kind() == reflect.Ptr {
+				if sf.IsNil() {
+					key = nilKey
+				} else {
+					key = sf.Elem().Interface()
+				}
+			} else {
+				key = sf.Interface()
 			}
+
+			if _, ok := seen[key]; ok {
+				return false
+			}
+			seen[key] = struct{}{}
 		}
-		return fieldlen == m.Len()
+
+		return true
+
 	case reflect.Map:
-		var m reflect.Value
-		if field.Type().Elem().Kind() == reflect.Ptr {
-			m = reflect.MakeMap(reflect.MapOf(field.Type().Elem().Elem(), v.Type()))
-		} else {
-			m = reflect.MakeMap(reflect.MapOf(field.Type().Elem(), v.Type()))
-		}
+		seen := make(map[interface{}]struct{})
 
 		for _, k := range field.MapKeys() {
-			m.SetMapIndex(reflect.Indirect(field.MapIndex(k)), v)
+			val := field.MapIndex(k)
+
+			var key interface{}
+
+			if val.Kind() == reflect.Ptr {
+				if val.IsNil() {
+					key = nilKey
+				} else {
+					key = val.Elem().Interface() // <-- compare underlying value
+				}
+			} else {
+				key = val.Interface()
+			}
+
+			if _, ok := seen[key]; ok {
+				return false
+			}
+			seen[key] = struct{}{}
 		}
 
-		return field.Len() == m.Len()
+		return true
+
 	default:
 		if parent := fl.Parent(); parent.Kind() == reflect.Struct {
 			uniqueField := parent.FieldByName(param)
-			if uniqueField == reflect.ValueOf(nil) {
+			if !uniqueField.IsValid() {
 				panic(fmt.Sprintf("Bad field name provided %s", param))
 			}
 

validator_test.go

@@ -10931,6 +10931,114 @@ func TestUniqueValidationStructPtrSlice(t *testing.T) {
 	PanicMatches(t, func() { _ = validate.Var(testStructs, "unique=C") }, "Bad field name C")
 }
 
+func TestUniqueValidationNilPtrSlice(t *testing.T) {
+	validate := New()
+
+	type Inner struct {
+		Name string
+	}
+
+	t.Run("unique_field_single_nil_ptr", func(t *testing.T) {
+		// A single nil element should not panic and should pass (it's unique by itself)
+		s := struct {
+			F1 []*Inner `validate:"unique=Name"`
+		}{F1: []*Inner{nil}}
+		errs := validate.Struct(s)
+		if errs != nil {
+			t.Fatalf("single nil element should pass unique=Name validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_field_duplicate_nil_ptrs", func(t *testing.T) {
+		// Two nil elements should not panic and should fail (not unique)
+		s := struct {
+			F1 []*Inner `validate:"unique=Name"`
+		}{F1: []*Inner{nil, nil}}
+		errs := validate.Struct(s)
+		if errs == nil {
+			t.Fatal("duplicate nil elements should fail unique=Name validation")
+		}
+	})
+
+	t.Run("unique_field_nil_and_non_nil", func(t *testing.T) {
+		// One nil and one non-nil should pass (they are different)
+		s := struct {
+			F1 []*Inner `validate:"unique=Name"`
+		}{F1: []*Inner{nil, {Name: "abc"}}}
+		errs := validate.Struct(s)
+		if errs != nil {
+			t.Fatalf("nil and non-nil elements should pass unique=Name validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_no_param_single_nil_ptr", func(t *testing.T) {
+		// A single nil element without param should not panic
+		s := struct {
+			F1 []*Inner `validate:"unique"`
+		}{F1: []*Inner{nil}}
+		errs := validate.Struct(s)
+		if errs != nil {
+			t.Fatalf("single nil element should pass unique validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_no_param_duplicate_nil_ptrs", func(t *testing.T) {
+		// Two nil elements without param should fail
+		s := struct {
+			F1 []*Inner `validate:"unique"`
+		}{F1: []*Inner{nil, nil}}
+		errs := validate.Struct(s)
+		if errs == nil {
+			t.Fatal("duplicate nil elements should fail unique validation")
+		}
+	})
+
+	t.Run("unique_no_param_nil_and_non_nil", func(t *testing.T) {
+		// One nil and one non-nil should pass
+		s := struct {
+			F1 []*Inner `validate:"unique"`
+		}{F1: []*Inner{nil, {Name: "abc"}}}
+		errs := validate.Struct(s)
+		if errs != nil {
+			t.Fatalf("nil and non-nil elements should pass unique validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_map_nil_values", func(t *testing.T) {
+		// Map with nil pointer values should not panic
+		m := map[string]*string{"one": nil, "two": nil}
+		errs := validate.Var(m, "unique")
+		if errs == nil {
+			t.Fatal("duplicate nil map values should fail unique validation")
+		}
+	})
+
+	t.Run("unique_map_single_nil_value", func(t *testing.T) {
+		m := map[string]*string{"one": nil}
+		errs := validate.Var(m, "unique")
+		if errs != nil {
+			t.Fatalf("single nil map value should pass unique validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_map_nil_and_non_nil", func(t *testing.T) {
+		a := "hello"
+		m := map[string]*string{"one": nil, "two": &a}
+		errs := validate.Var(m, "unique")
+		if errs != nil {
+			t.Fatalf("nil and non-nil map values should pass unique validation, got: %v", errs)
+		}
+	})
+
+	t.Run("unique_slice_with_nil_and_zero_value_struct", func(t *testing.T) {
+		s := []*Inner{nil, {Name: ""}}
+		errs := validate.Var(s, "unique")
+		if errs != nil {
+			t.Fatalf("nil and zero value struct should pass unique validation, got: %v", errs)
+		}
+	})
+}
+
 func TestHTMLValidation(t *testing.T) {
 	tests := []struct {
 		param    string