feat(AIP-123): add singular and plural validation (#1143)

Matching AIP-123 in requiring singular and plural annotations,
and for singular matching the lowerCamelCase of type.

Wrote custom ToUpperCamelCase as existing one does not consider
underscores / dashes as invalid characters, which are considered
delimiters in the camel case conversion. Further investigation on replacing
it with #1150.

docs/rules/0123/resource-plural.md

@@ -0,0 +1,74 @@
+---
+rule:
+  aip: 123
+  name: [core, '0123', resource-plural]
+  summary: Resource plural is required
+permalink: /123/resource-plural
+redirect_from:
+  - /0123/resource-plural
+---
+
+# Resource type name
+
+This rule enforces that messages that have a `google.api.resource` annotation,
+have a properly formatted `plural`, as described in [AIP-123][].
+
+## Details
+
+This rule scans messages with a `google.api.resource` annotation, and
+verifies the `plural` field exists.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+message Book {
+  // no plural annotation
+  option (google.api.resource) = {
+    type: "library.googleapis.com/BookShelf"
+    pattern: "publishers/{publisher}/bookShelves/{book_shelf}"
+  };
+
+  string name = 1;
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/BookShelf"
+    pattern: "publishers/{publisher}/bookShelves/{book_shelf}"
+    plural: "bookShelves",
+  };
+
+  string name = 1;
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the message.
+
+```proto
+// (-- api-linter: core::0123::resource-plural=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Genre/Mystery/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+  };
+
+  string name = 1;
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-123]: http://aip.dev/123
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

docs/rules/0123/resource-singular.md

@@ -0,0 +1,76 @@
+---
+rule:
+  aip: 123
+  name: [core, '0123', resource-singular]
+  summary: Resource singular is required and must be lowerCamelCase of type
+permalink: /123/resource-singular
+redirect_from:
+  - /0123/resource-singular
+---
+
+# Resource type name
+
+This rule enforces that messages that have a `google.api.resource` annotation,
+have a properly formatted `singular`, as described in [AIP-123][].
+
+## Details
+
+This rule scans messages with a `google.api.resource` annotation, and validates
+the format of the `singular` field is the lower camel case of type.
+
+## Examples
+
+**Incorrect** code for this rule:
+
+```proto
+// Incorrect.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/BookShelf"
+    pattern: "publishers/{publisher}/bookShelves/{book_shelf}"
+    // does not match type.
+    singular: "shelf",
+  };
+
+  string name = 1;
+}
+```
+
+**Correct** code for this rule:
+
+```proto
+// Correct.
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/BookShelf"
+    pattern: "publishers/{publisher}/bookShelves/{book_shelf}"
+    singular: "bookShelf",
+  };
+
+  string name = 1;
+}
+```
+
+## Disabling
+
+If you need to violate this rule, use a leading comment above the message.
+
+```proto
+// (-- api-linter: core::0123::resource-singular=disabled
+//     aip.dev/not-precedent: We need to do this because reasons. --)
+message Book {
+  option (google.api.resource) = {
+    type: "library.googleapis.com/Genre/Mystery/Book"
+    pattern: "publishers/{publisher}/books/{book}"
+    singular: "shelf",
+  };
+
+  string name = 1;
+}
+```
+
+If you need to violate this rule for an entire file, place the comment at the
+top of the file.
+
+[aip-123]: http://aip.dev/123
+[aip.dev/not-precedent]: https://aip.dev/not-precedent

rules/aip0123/aip0123.go

@@ -35,7 +35,9 @@ func AddRules(r lint.RuleRegistry) error {
 		resourceAnnotation,
 		resourceNameField,
 		resourcePattern,
+		resourcePlural,
 		resourceReferenceType,
+		resourceSingular,
 		resourceTypeName,
 		resourceVariables,
 		resourceDefinitionVariables,

rules/aip0123/resource_plural.go

@@ -0,0 +1,52 @@
+// 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 aip0123
+
+import (
+	"fmt"
+
+	"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 resourcePlural = &lint.MessageRule{
+	Name:   lint.NewRuleName(123, "resource-plural"),
+	OnlyIf: hasResourceAnnotation,
+	LintMessage: func(m *desc.MessageDescriptor) []lint.Problem {
+		r := utils.GetResource(m)
+		l := locations.MessageResource(m)
+		p := r.GetPlural()
+		pLower := utils.ToLowerCamelCase(p)
+		if p == "" {
+			return []lint.Problem{{
+				Message:    "Resources should declare plural.",
+				Descriptor: m,
+				Location:   l,
+			}}
+		}
+		if pLower != p {
+			return []lint.Problem{{
+				Message: fmt.Sprintf(
+					"Resource plural should be lowerCamelCase: %q", pLower,
+				),
+				Descriptor: m,
+				Location:   l,
+			}}
+		}
+		return nil
+	},
+}

rules/aip0123/resource_plural_test.go

@@ -0,0 +1,73 @@
+// 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 aip0123
+
+import (
+	"testing"
+
+	"github.com/googleapis/api-linter/rules/internal/testutils"
+)
+
+func TestResourcePlural(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		Plural   string
+		problems testutils.Problems
+	}{
+		{
+			"Valid",
+			`plural: "bookShelves"`,
+			nil,
+		},
+		{
+			"InvalidMissing",
+			``,
+			testutils.Problems{{
+				Message: "Resources should declare plural",
+			}},
+		},
+		{
+			"InvalidUpperCamel",
+			`plural: "BookShelves"`,
+			testutils.Problems{{
+				Message: "Resource plural should be lowerCamelCase",
+			}},
+		},
+		{
+			"InvalidDash",
+			`plural: "Book-Shelves"`,
+			testutils.Problems{{
+				Message: "Resource plural should be lowerCamelCase",
+			}},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			f := testutils.ParseProto3Tmpl(t, `
+			import "google/api/resource.proto";
+			message Book {
+				option (google.api.resource) = {
+					type: "library.googleapis.com/BookShelf"
+					pattern: "publishers/{publisher}/bookShelves/{book_shelf}"
+					{{.Plural}}
+				};
+				string name = 1;
+			}
+			`, test)
+			m := f.GetMessageTypes()[0]
+			if diff := test.problems.SetDescriptor(m).Diff(resourcePlural.Lint(f)); diff != "" {
+				t.Error(diff)
+			}
+		})
+	}
+}

rules/aip0123/resource_singular.go

@@ -0,0 +1,54 @@
+// 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 aip0123
+
+import (
+	"fmt"
+
+	"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 resourceSingular = &lint.MessageRule{
+	Name:   lint.NewRuleName(123, "resource-singular"),
+	OnlyIf: hasResourceAnnotation,
+	LintMessage: func(m *desc.MessageDescriptor) []lint.Problem {
+		r := utils.GetResource(m)
+		l := locations.MessageResource(m)
+		s := r.GetSingular()
+		_, typeName, ok := utils.SplitResourceTypeName(r.GetType())
+		lowerTypeName := utils.ToLowerCamelCase(typeName)
+		if s == "" {
+			return []lint.Problem{{
+				Message:    fmt.Sprintf("Resources should declare singular: %q", lowerTypeName),
+				Descriptor: m,
+				Location:   l,
+			}}
+		}
+		if !ok || lowerTypeName != s {
+			return []lint.Problem{{
+				Message: fmt.Sprintf(
+					"Resource singular should be lower camel case of type: %q",
+					lowerTypeName,
+				),
+				Descriptor: m,
+				Location:   l,
+			}}
+		}
+		return nil
+	},
+}