build: fix docs not displaying inherited members properly (#17145)

Recently due to the MDC prototypes, we have multiple layers of inheritance. Apparently
our current docs tooling sometimes does not display inherited members which are coming
from implicitly inherited class-like documents.

For example: see how the `MatTabLink` docs broke when the MDC prototype
landed: 492fdcc40

Author: devversion

tools/dgeni/processors/docs-private-filter.ts

@@ -9,6 +9,7 @@ import {getDocsPublicTag, isPublicDoc} from '../common/private-docs';
 export class DocsPrivateFilter implements Processor {
   name = 'docs-private-filter';
   $runBefore = ['categorizer'];
+  $runAfter = ['merge-inherited-properties'];
 
   $process(docs: DocCollection) {
     return docs.filter(doc => {

tools/dgeni/processors/merge-inherited-properties.ts

@@ -1,5 +1,6 @@
 import {DocCollection, Processor} from 'dgeni';
 import {ClassExportDoc} from 'dgeni-packages/typescript/api-doc-types/ClassExportDoc';
+import {ClassLikeExportDoc} from 'dgeni-packages/typescript/api-doc-types/ClassLikeExportDoc';
 import {MemberDoc} from 'dgeni-packages/typescript/api-doc-types/MemberDoc';
 
 /**
@@ -11,18 +12,30 @@ export class MergeInheritedProperties implements Processor {
   $runBefore = ['categorizer'];
 
   $process(docs: DocCollection) {
-    return docs
-      .filter(doc => doc.docType === 'class')
-      .forEach(doc => this._addInheritedProperties(doc));
+    return docs.filter(doc => doc.docType === 'class')
+        .forEach(doc => this._addInheritedProperties(doc));
   }
 
-  private _addInheritedProperties(doc: ClassExportDoc) {
-    doc.implementsClauses.filter(clause => clause.doc).forEach(clause => {
-      clause.doc!.members.forEach(member => this._addMemberDocIfNotPresent(doc, member));
-    });
+  /** Gets all class like export documents which the given doc inherits from. */
+  private _getBaseDocuments(doc: ClassLikeExportDoc): ClassLikeExportDoc[] {
+    const directBaseDocs = [
+      ...doc.implementsClauses.filter(clause => clause.doc).map(d => d.doc!),
+      ...doc.extendsClauses.filter(clause => clause.doc).map(d => d.doc!),
+    ];
 
-    doc.extendsClauses.filter(clause => clause.doc).forEach(clause => {
-      clause.doc!.members.forEach(member => this._addMemberDocIfNotPresent(doc, member));
+    return [
+      ...directBaseDocs,
+      // recursively collect base documents of direct base documents.
+      ...directBaseDocs.reduce(
+          (res: ClassLikeExportDoc[], d) => res.concat(this._getBaseDocuments(d)), []),
+    ];
+  }
+
+  private _addInheritedProperties(doc: ClassExportDoc) {
+    // Note that we need to get check all base documents. We cannot assume
+    // that directive base documents already have merged inherited members.
+    this._getBaseDocuments(doc).forEach(d => {
+      d.members.forEach(member => this._addMemberDocIfNotPresent(doc, member));
     });
   }