feat(AIP-134): update_mask must be OPTIONAL

docs/rules/0134/update-mask-optional-behavior.md

@@ -0,0 +1,72 @@
+---
+rule:
+  aip: 134
+  name: [core, '0134', update-mask-optional-behavior]
+  summary: Standard Update `update_mask` field must be `OPTIONAL`.
+permalink: /134/update-mask-optional-behavior
+redirect_from:
+  - /0134/update-mask-optional-behavior
+---
+
+# Update methods: Mask field expected behavior
+
+This rule enforces that the `update_mask` field of a Standard `Update` request
+uses `google.api.field_behavior = OPTIONAL`, as mandated in [AIP-134][].
+
+## Details
+
+This rule looks at any field named `update_mask` that's in a `Update*Request`
+and complains if it the field is not annotated with
+`google.api.field_behavior = OPTIONAL`.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+message UpdateBookRequest {
+  Book book = 1;
+
+  // Incorrect. Must be `OPTIONAL`.
+  google.protobuf.FieldMask update_mask = 2 [  
+    (google.api.field_behavior) = REQUIRED
+  ];
+}
+```
+
+
+**Correct** code for this rule:
+
+```proto
+message UpdateBookRequest {
+  Book book = 1;
+
+  // Correct.
+  google.protobuf.FieldMask update_mask = 2 [
+    (google.api.field_behavior) = OPTIONAL
+  ];
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the message.
+Remember to also include an [aip.dev/not-precedent][] comment explaining why.
+
+```proto
+message UpdateBookRequest {
+  Book book = 1;
+
+  // (-- api-linter: core::0134::update-mask-optional-behavior=disabled
+  //     aip.dev/not-precedent: We need to do this because reasons. --)
+  google.protobuf.FieldMask update_mask = 2 [  
+    (google.api.field_behavior) = REQUIRED
+  ];
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-134]: https://aip.dev/134
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

locations/field_locations.go

@@ -35,6 +35,12 @@ func FieldResourceReference(f *desc.FieldDescriptor) *dpb.SourceCodeInfo_Locatio
 	return pathLocation(f, 8, int(apb.E_ResourceReference.TypeDescriptor().Number())) // FieldDescriptor.options == 8
 }
 
+// FieldBehavior returns the precise location for a field's
+// field_behavior annotation.
+func FieldBehavior(f *desc.FieldDescriptor) *dpb.SourceCodeInfo_Location {
+	return pathLocation(f, 8, int(apb.E_FieldBehavior.TypeDescriptor().Number())) // FieldDescriptor.options == 8
+}
+
 // FieldType returns the precise location for a field's type.
 func FieldType(f *desc.FieldDescriptor) *dpb.SourceCodeInfo_Location {
 	if f.GetMessageType() != nil || f.GetEnumType() != nil {

rules/aip0134/aip0134.go

@@ -42,6 +42,7 @@ func AddRules(r lint.RuleRegistry) error {
 		responseLRO,
 		synonyms,
 		unknownFields,
+		updateMaskOptionalBehavior,
 	)
 }
 

rules/aip0134/update_mask_optional_behavior.go

@@ -0,0 +1,42 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0134
+
+import (
+	"github.com/googleapis/api-linter/lint"
+	"github.com/googleapis/api-linter/locations"
+	"github.com/googleapis/api-linter/rules/internal/utils"
+	"github.com/jhump/protoreflect/desc"
+)
+
+var updateMaskOptionalBehavior = &lint.FieldRule{
+	Name: lint.NewRuleName(134, "update-mask-optional-behavior"),
+	OnlyIf: func(f *desc.FieldDescriptor) bool {
+		return f.GetName() == "update_mask" && utils.IsUpdateRequestMessage(f.GetOwner())
+	},
+	LintField: func(f *desc.FieldDescriptor) []lint.Problem {
+		behaviors := utils.GetFieldBehavior(f)
+		if !behaviors.Contains("OPTIONAL") {
+			return []lint.Problem{
+				{
+					Message:    "Standard Update field `update_mask` must have `OPTIONAL` behavior",
+					Descriptor: f,
+					Location:   locations.FieldBehavior(f),
+				},
+			}
+		}
+		return nil
+	},
+}

rules/aip0134/update_mask_optional_behavior_test.go

@@ -0,0 +1,51 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package aip0134
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestUpdateMaskOptionalBehavior(t *testing.T) {
+	tests := []struct {
+		name     string
+		Behavior string
+		problems testutils.Problems
+	}{
+		{"Valid", "[(google.api.field_behavior) = OPTIONAL]", nil},
+		{"InvalidWrong", "[(google.api.field_behavior) = REQUIRED]", testutils.Problems{{Message: "must have `OPTIONAL`"}}},
+		{"InvalidMissing", "", testutils.Problems{{Message: "must have `OPTIONAL`"}}},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			file := testutils.ParseProto3Tmpl(t, `
+				import "google/api/field_behavior.proto";
+				import "google/protobuf/field_mask.proto";
+				message UpdateBookRequest {
+					Book book = 1;
+					google.protobuf.FieldMask update_mask = 2 {{.Behavior}};
+				}
+				message Book {}
+			`, test)
+			field := file.GetMessageTypes()[0].FindFieldByName("update_mask")
+			problems := updateMaskOptionalBehavior.Lint(file)
+			if diff := test.problems.SetDescriptor(field).Diff(problems); diff != "" {
+				t.Errorf(diff)
+			}
+		})
+	}
+}

rules/aip0203/resource_name_identifier.go

@@ -34,7 +34,7 @@ var resourceNameIdentifier = &lint.MessageRule{
 			return []lint.Problem{{
 				Message:    "resource name field must have field_behavior IDENTIFIER",
 				Descriptor: f,
-				Location:   locations.FieldOption(f, fpb.E_FieldBehavior),
+				Location:   locations.FieldBehavior(f),
 			}}
 		}