feat(compiler): add docs extraction for type aliases (#52118)

This commit adds support for extracting type alises. It currently
extracts the raw written type from the source without performing any
resolution, such as for resolving `typeof` queries, as current Angular
public APIs do not rely on this.

PR Close #52118

packages/compiler-cli/src/ngtsc/docs/src/entities.ts

@@ -62,6 +62,9 @@ export interface ConstantEntry extends DocEntry {
   type: string;
 }
 
+/** Documentation entity for a type alias. */
+export type TypeAliasEntry = ConstantEntry;
+
 /** Documentation entity for a TypeScript class. */
 export interface ClassEntry extends DocEntry {
   isAbstract: boolean;

packages/compiler-cli/src/ngtsc/docs/src/extractor.ts

@@ -17,6 +17,7 @@ import {extractClass, extractInterface} from './class_extractor';
 import {extractConstant, isSyntheticAngularConstant} from './constant_extractor';
 import {DocEntry} from './entities';
 import {isAngularPrivateName} from './filters';
+import {extractTypeAlias} from './type_alias_extractor';
 
 type DeclarationWithExportName = readonly[string, ts.Declaration];
 
@@ -72,6 +73,10 @@ export class DocsExtractor {
       return extractConstant(node, this.typeChecker);
     }
 
+    if (ts.isTypeAliasDeclaration(node)) {
+      return extractTypeAlias(node);
+    }
+
     if (ts.isEnumDeclaration(node)) {
       return extractEnum(node, this.typeChecker);
     }

packages/compiler-cli/src/ngtsc/docs/src/type_alias_extractor.ts

@@ -0,0 +1,27 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+import ts from 'typescript';
+
+import {EntryType} from './entities';
+import {extractJsDocDescription, extractJsDocTags, extractRawJsDoc} from './jsdoc_extractor';
+
+/** Extract the documentation entry for a type alias. */
+export function extractTypeAlias(declaration: ts.TypeAliasDeclaration) {
+  // TODO: this does not yet resolve type queries (`typeof`). We may want to
+  //     fix this eventually, but for now it does not appear that any type aliases in
+  //     Angular's public API rely on this.
+
+  return {
+    name: declaration.name.getText(),
+    type: declaration.type.getText(),
+    entryType: EntryType.TypeAlias,
+    rawComment: extractRawJsDoc(declaration),
+    description: extractJsDocDescription(declaration),
+    jsdocTags: extractJsDocTags(declaration),
+  };
+}

packages/compiler-cli/test/ngtsc/doc_extraction/type_alias_doc_extraction_spec.ts

@@ -0,0 +1,61 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {DocEntry} from '@angular/compiler-cli/src/ngtsc/docs';
+import {EntryType, TypeAliasEntry} from '@angular/compiler-cli/src/ngtsc/docs/src/entities';
+import {runInEachFileSystem} from '@angular/compiler-cli/src/ngtsc/file_system/testing';
+import {loadStandardTestFiles} from '@angular/compiler-cli/src/ngtsc/testing';
+
+import {NgtscTestEnvironment} from '../env';
+
+const testFiles = loadStandardTestFiles({fakeCore: true, fakeCommon: true});
+
+runInEachFileSystem(os => {
+  let env!: NgtscTestEnvironment;
+
+  describe('ngtsc type alias docs extraction', () => {
+    beforeEach(() => {
+      env = NgtscTestEnvironment.setup(testFiles);
+      env.tsconfig();
+    });
+
+    it('should extract type aliases based on primitives', () => {
+      env.write('index.ts', `
+        export type SuperNumber = number | string;
+      `);
+
+      const docs: DocEntry[] = env.driveDocsExtraction('index.ts');
+      expect(docs.length).toBe(1);
+
+      const typeAliasEntry = docs[0] as TypeAliasEntry;
+      expect(typeAliasEntry.name).toBe('SuperNumber');
+      expect(typeAliasEntry.entryType).toBe(EntryType.TypeAlias);
+      expect(typeAliasEntry.type).toBe('number | string');
+    });
+
+    it('should extract type aliases for objects', () => {
+      env.write('index.ts', `
+        export type UserProfile = {
+          name: string;
+          age: number;
+        };
+      `);
+
+      const docs: DocEntry[] = env.driveDocsExtraction('index.ts');
+      expect(docs.length).toBe(1);
+
+      const typeAliasEntry = docs[0] as TypeAliasEntry;
+      expect(typeAliasEntry.name).toBe('UserProfile');
+      expect(typeAliasEntry.entryType).toBe(EntryType.TypeAlias);
+      expect(typeAliasEntry.type).toBe(`{
+          name: string;
+          age: number;
+        }`);
+    });
+  });
+});