feat(AIP-203): require field_behavior

docs/rules/0203/field-behavior-required.md

@@ -0,0 +1,70 @@
+---
+rule:
+  aip: 203
+  name: [core, '0203', field-behavior-required]
+  summary: Field behavior is required, and must have one of OUTPUT_ONLY,
+  REQUIRED, or OPTIONAL.
+permalink: /203/field-behavior-required
+redirect_from:
+  - /0203/field-behavior-required
+---
+
+# Field Behavior Required
+
+This rule enforces that each field in a message used in a request has a
+`google.api.field_behavior` annotation with valid values, as mandated by
+[AIP-203][].
+
+## Details
+
+This rule looks at all fields and ensures they have a
+`google.api.field_behavior` annotation. It also verifies that they have at least
+one of the options `OUTPUT_ONLY`, `REQUIRED`, or `OPTIONAL`: all fields must
+fall into one of these categories.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+message Book {
+  string name = 1;
+
+  // No field behavior
+  optional string title = 2;
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+message Book {
+  string name = 1;
+
+  string title = 2 [(google.api.field_behavior) = REQUIRED];
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the field.
+Remember to also include an [aip.dev/not-precedent][] comment explaining why.
+
+```proto
+message Book {
+  string name = 1;
+
+  // Required. The title of the book.
+  // (-- api-linter: core::0203::field-behavior-required=disabled
+  //     aip.dev/not-precedent: We need to do this because reasons. --)
+  optional string title = 2;
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-203]: https://aip.dev/203
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

docs/rules/0203/required-and-optional.md

@@ -35,7 +35,7 @@ message Book {
 **Correct** code for this rule:
 
 ```proto
-// Incorrect.
+// Correct.
 message Book {
   string name = 1;
 

rules/aip0203/aip0203.go

@@ -31,11 +31,11 @@ var standardFields = stringset.New("etag")
 func AddRules(r lint.RuleRegistry) error {
 	return r.Register(
 		203,
+		fieldBehaviorRequired,
 		inputOnly,
 		immutable,
 		optional,
 		optionalBehaviorConflict,
-		optionalBehaviorConsistency,
 		outputOnly,
 		required,
 		requiredAndOptional,

rules/aip0203/field_behavior_required.go

@@ -0,0 +1,75 @@
+// Copyright 2023 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 aip0203
+
+import (
+	"fmt"
+
+	"bitbucket.org/creachadair/stringset"
+	"github.com/googleapis/api-linter/lint"
+	"github.com/googleapis/api-linter/rules/internal/utils"
+	"github.com/jhump/protoreflect/desc"
+)
+
+var minimumRequiredFieldBehavior = stringset.New(
+	"OPTIONAL", "REQUIRED", "OUTPUT_ONLY", "IMMUTABLE",
+)
+
+var fieldBehaviorRequired = &lint.MethodRule{
+	Name: lint.NewRuleName(203, "field-behavior-required"),
+	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
+		// we only check requests, as OutputTypes are always
+		// OUTPUT_ONLY
+		it := m.GetInputType()
+		return checkFields(it)
+	},
+}
+
+func checkFields(m *desc.MessageDescriptor) []lint.Problem {
+	problems := []lint.Problem{}
+	for _, f := range m.GetFields() {
+		asMessage := f.GetMessageType()
+		if asMessage != nil {
+			problems = append(problems, checkFields(asMessage)...)
+		}
+		p := checkFieldBehavior(f)
+		if p != nil {
+			problems = append(problems, *p)
+		}
+	}
+	return problems
+}
+
+func checkFieldBehavior(f *desc.FieldDescriptor) *lint.Problem {
+	fieldBehavior := utils.GetFieldBehavior(f)
+	if len(fieldBehavior) == 0 {
+		return &lint.Problem{
+			Message: fmt.Sprintf("google.api.field_behavior annotation must be set, and have one of %v",
+				minimumRequiredFieldBehavior,
+			),
+			Descriptor: f,
+		}
+	}
+	// check for at least one valid annotation
+	if !minimumRequiredFieldBehavior.Intersects(fieldBehavior) {
+		return &lint.Problem{
+			Message: fmt.Sprintf(
+				"google.api.field_behavior must have at least one of the following behaviors set: %v",
+				minimumRequiredFieldBehavior,
+			),
+			Descriptor: f,
+		}
+	}
+	return nil
+}