chore: fixes some issues that happen with closure compiler. (#10392)

modules/@angular/compiler/src/compiler.ts

@@ -222,6 +222,6 @@ function _lastDefined<T>(args: T[]): T {
 
 function _mergeArrays(parts: any[][]): any[] {
   let result: any[] = [];
-  parts.forEach((part) => result.push(...part));
+  parts.forEach((part) => part && result.push(...part));
   return result;
 }

modules/@angular/core/src/metadata/ng_module.ts

@@ -146,15 +146,15 @@ export class NgModuleMetadata extends InjectableMetadata implements NgModuleMeta
 
   schemas: Array<SchemaMetadata|any[]>;
 
-  constructor(
-      {providers, declarations, imports, exports, entryComponents,
-       schemas}: NgModuleMetadataType = {}) {
+  constructor(options: NgModuleMetadataType = {}) {
+    // We cannot use destructuring of the constructor argument because `exports` is a
+    // protected symbol in CommonJS and closure tries to aggressively optimize it away.
     super();
-    this._providers = providers;
-    this.declarations = declarations;
-    this.imports = imports;
-    this.exports = exports;
-    this.entryComponents = entryComponents;
-    this.schemas = schemas;
+    this._providers = options.providers;
+    this.declarations = options.declarations;
+    this.imports = options.imports;
+    this.exports = options.exports;
+    this.entryComponents = options.entryComponents;
+    this.schemas = options.schemas;
   }
 }

tools/public_api_guard/core/index.d.ts

@@ -805,7 +805,7 @@ export declare class NgModuleMetadata extends InjectableMetadata implements NgMo
     imports: Array<Type | ModuleWithProviders | any[]>;
     providers: any[];
     schemas: Array<SchemaMetadata | any[]>;
-    constructor({providers, declarations, imports, exports, entryComponents, schemas}?: NgModuleMetadataType);
+    constructor(options?: NgModuleMetadataType);
 }
 
 /** @experimental */