feat: Add rule for AIP-165 HTTP parent variable (#814)

docs/rules/0165/http-parent-variable.md

@@ -0,0 +1,80 @@
+---
+rule:
+  aip: 165
+  name: [core, '0165', http-parent-variable]
+  summary: Purge methods must map the parent field to the URI.
+permalink: /165/http-parent-variable
+redirect_from:
+  - /0165/http-parent-variable
+---
+
+# Purge methods: HTTP URI parent variable
+
+This rule enforces that all `Purge` RPCs map the `parent` field to the HTTP
+URI, as mandated in [AIP-165][].
+
+## Details
+
+This rule looks at any message beginning with `Purge`, and complains
+if the `parent` variable is not included in the URI. It _does_ check additional
+bindings if they are present.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+rpc PurgeBooks(PurgeBooksRequest) returns (google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/publishers/*/books:purge"  // The `parent` field should be extracted.
+    body: "*"
+  };
+  option (google.longrunning.operation_info) = {
+    response_type: "PurgeBooksResponse"
+    metadata_type: "PurgeBooksMetadata"
+  };
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+rpc PurgeBooks(PurgeBooksRequest) returns (google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/{parent=publishers/*}/books:purge"
+    body: "*"
+  };
+  option (google.longrunning.operation_info) = {
+    response_type: "PurgeBooksResponse"
+    metadata_type: "PurgeBooksMetadata"
+  };
+}
+```
+
+## 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: core::0165::http-parent-variable=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+rpc PurgeBooks(PurgeBooksRequest) returns (google.longrunning.Operation) {
+  option (google.api.http) = {
+    post: "/v1/publishers/*/books:purge"
+    body: "*""
+  };
+  option (google.longrunning.operation_info) = {
+    response_type: "PurgeBooksResponse"
+    metadata_type: "PurgeBooksMetadata"
+  };
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-165]: https://aip.dev/165
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip0165/aip0165.go

@@ -28,6 +28,7 @@ func AddRules(r lint.RuleRegistry) error {
 		165,
 		httpBody,
 		httpMethod,
+		httpParentVariable,
 		httpURISuffix,
 		requestFilterBehavior,
 		requestFilterField,

rules/aip0165/http_parent_variable.go

@@ -0,0 +1,43 @@
+// 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 aip0165
+
+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"
+)
+
+// Purge methods should have a parent variable in the URI unless the resource is top-level.
+var httpParentVariable = &lint.MethodRule{
+	Name: lint.NewRuleName(165, "http-parent-variable"),
+	OnlyIf: func(m *desc.MethodDescriptor) bool {
+		return isPurgeMethod(m) && m.GetInputType().FindFieldByName("parent") != nil
+	},
+	LintMethod: func(m *desc.MethodDescriptor) []lint.Problem {
+		for _, httpRule := range utils.GetHTTPRules(m) {
+			if _, ok := httpRule.GetVariables()["parent"]; !ok {
+				return []lint.Problem{{
+					Message:    "Purge methods should include the `parent` field in the URI.",
+					Descriptor: m,
+					Location:   locations.MethodHTTPRule(m),
+				}}
+			}
+		}
+
+		return nil
+	},
+}

rules/aip0165/http_parent_variable_test.go

@@ -0,0 +1,60 @@
+// Copyright 2019 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 aip0165
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestHTTPParentVariable(t *testing.T) {
+	tests := []struct {
+		testName   string
+		URI        string
+		MethodName string
+		Field      string
+		problems   testutils.Problems
+	}{
+		{"Valid", "/v1/{parent=publishers/*/books/*}", "PurgeBooks", "string parent = 1;", nil},
+		{"InvalidVarParent", "/v1/{book=publishers/*/books/*}", "PurgeBooks", "string parent = 1;", testutils.Problems{{Message: "`parent` field"}}},
+		{"NoVarParent", "/v1/publishers/*/books/*", "PurgeBooks", "string parent = 1;", testutils.Problems{{Message: "`parent` field"}}},
+		{"NoParent", "/v1/books/*", "PurgeBooks", "", nil},
+		{"Irrelevant", "/v1/{book=publishers/*/books/*}", "BuildBook", "string parent = 1;", nil},
+	}
+
+	for _, test := range tests {
+		t.Run(test.testName, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+				import "google/api/annotations.proto";
+				  service Library {
+					rpc {{.MethodName}}({{.MethodName}}Request) returns ({{.MethodName}}Response) {
+						option (google.api.http) = {
+							post: "{{.URI}}"
+						};
+					}
+				}
+				message {{.MethodName}}Request {
+					{{.Field}}
+				}
+				message {{.MethodName}}Response {}
+			`, test)
+			method := f.GetServices()[0].GetMethods()[0]
+			if diff := test.problems.SetDescriptor(method).Diff(httpParentVariable.Lint(f)); diff != "" {
+				t.Error(diff)
+			}
+		})
+	}
+}