feat(compiler-cli): support metadata file aliases

packages/compiler-cli/src/compiler_host.ts

@@ -207,7 +207,11 @@ export class CompilerHost implements AotCompilerHost {
       return metadatas;
     }
     try {
-      const metadataOrMetadatas = JSON.parse(this.context.readFile(filePath));
+      let metadataOrMetadatas = JSON.parse(this.context.readFile(filePath));
+      while (metadataOrMetadatas.alias) {
+        filePath = path.join(path.dirname(filePath), metadataOrMetadatas.alias);
+        metadataOrMetadatas = JSON.parse(this.context.readFile(filePath));
+      }
       const metadatas: ModuleMetadata[] = metadataOrMetadatas ?
           (Array.isArray(metadataOrMetadatas) ? metadataOrMetadatas : [metadataOrMetadatas]) :
           [];

packages/compiler-cli/test/aot_host_spec.ts

@@ -202,6 +202,10 @@ describe('CompilerHost', () => {
       {__symbolic: 'module', version: 3, metadata: {}, exports: [{from: './lib/utils'}]}
     ]);
   });
+
+  it('should follow metadata aliases', () => {
+    expect(hostNestedGenDir.getMetadataFor('alias/file.d.ts')).toEqual([dummyMetadata]);
+  });
 });
 
 const dummyModule = 'export let foo: any[];';
@@ -237,6 +241,13 @@ const FILES: Entry = {
           'empty.metadata.json': '[]',
         }
       },
+      'alias': {
+        'file.d.ts': dummyModule,
+        'file.metadata.json': '{ "alias": "sub/index.metadata.json"}',
+        'sub': {
+          'index.metadata.json': JSON.stringify(dummyMetadata)
+        }
+      },
       'metadata_versions': {
         'v1.d.ts': `
           import {ReExport} from './lib/utils2';