feat: enforce all required fields in method signatures (#894)

* feat: enforce all required fields in method signatures

docs/rules/4232/required-fields.md

@@ -0,0 +1,72 @@
+---
+rule:
+  aip: 4232
+  name: [client-libraries, '4232', required-fields]
+  summary: Method Signatures must contain all fields annotated as required.
+permalink: /4232/required-fields
+---
+
+# Method Signature: Required fields
+
+This rule enforces that all `google.api.method_signature` annotations contain
+all top-level request message fields that are annotated with `REQUIRED`, as 
+mandated in [AIP-4232][].
+
+## Details
+
+This rule looks at any RPC methods with a `google.api.method_signature`
+annotation, and complains if any request field annotated with `REQUIRED` is
+missing.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+rpc BatchDeleteBooks(BatchDeleteBooksRequest) returns (google.protobuf.Empty) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*}/books:batchDelete"
+    body: "*"
+  };
+  // The field "names" is annotated with REQUIRED and is missing from the
+  // method_signature.
+  option (google.api.method_signature) = "parent";
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+rpc BatchDeleteBooks(BatchDeleteBooksRequest) returns (google.protobuf.Empty) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*}/books:batchDelete"
+    body: "*"
+  };
+  option (google.api.method_signature) = "parent,names";
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the method.
+Remember to also include an [aip.dev/not-precedent][] comment explaining why.
+
+```proto
+// (-- api-linter: client-libraries::4232::required-fields=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+rpc BatchDeleteBooks(BatchDeleteBooksRequest) returns (google.protobuf.Empty) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*}/books:batchDelete"
+    body: "*"
+  };
+  option (google.api.method_signature) = "parent";
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-4232]: https://aip.dev/4232
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip4232/aip4232.go

@@ -27,6 +27,7 @@ func AddRules(r lint.RuleRegistry) error {
 	return r.Register(
 		4232,
 		repeatedFields,
+		requiredFields,
 	)
 }
 

rules/aip4232/required_fields.go

@@ -0,0 +1,56 @@
+// Copyright 2021 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 aip4232
+
+import (
+	"fmt"
+	"strings"
+
+	"bitbucket.org/creachadair/stringset"
+	"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"
+)
+
+// All fields annotated as REQUIRED must be in every method_signature.
+var requiredFields = &lint.MethodRule{
+	Name:   lint.NewRuleName(4232, "required-fields"),
+	OnlyIf: hasMethodSignatures,
+	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
+		var problems []lint.Problem
+		sigs := utils.GetMethodSignatures(m)
+		in := m.GetInputType()
+
+		requiredFields := []string{}
+		for _, f := range in.GetFields() {
+			if utils.GetFieldBehavior(f).Contains("REQUIRED") {
+				requiredFields = append(requiredFields, f.GetName())
+			}
+		}
+		for i, sig := range sigs {
+			sigset := stringset.New(sig...)
+			if !sigset.Contains(requiredFields...) {
+				problems = append(problems, lint.Problem{
+					Message:    fmt.Sprintf("Method signature %q missing at least one of the required fields: %q", strings.Join(sig, ","), strings.Join(requiredFields, ",")),
+					Descriptor: m,
+					Location:   locations.MethodSignature(m, i),
+				})
+			}
+		}
+
+		return problems
+	},
+}

rules/aip4232/required_fields_test.go

@@ -0,0 +1,58 @@
+// Copyright 2021 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 aip4232
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestRequiredFields(t *testing.T) {
+	tests := []struct {
+		testName      string
+		Signature     string
+		FieldBehavior string
+		problems      testutils.Problems
+	}{
+		{"Valid", "name,paperback_only", "REQUIRED", nil},
+		{"ValidNotRequired", "paperback_only", "OPTIONAL", nil},
+		{"Invalid", "paperback_only", "REQUIRED", testutils.Problems{{Message: "missing at least one"}}},
+	}
+
+	for _, test := range tests {
+		t.Run(test.testName, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+				import "google/api/client.proto";
+				import "google/api/field_behavior.proto";
+				service Library {
+					rpc ArchiveBook(ArchiveBookRequest) returns (ArchiveBookResponse) {
+						option (google.api.method_signature) = "{{.Signature}}";
+					}
+				}
+				message ArchiveBookRequest {
+					string name = 1 [(google.api.field_behavior) = {{.FieldBehavior}}];
+
+					bool paperback_only = 2;
+				}
+				message ArchiveBookResponse {}
+			`, test)
+			method := f.GetServices()[0].GetMethods()[0]
+			if diff := test.problems.SetDescriptor(method).Diff(requiredFields.Lint(f)); diff != "" {
+				t.Error(diff)
+			}
+		})
+	}
+}