feat(compiler): do not parse xtb messages not needed by angular (#14111)

fixes #14046

PR Close #14111

modules/@angular/compiler/src/i18n/serializers/xtb.ts

@@ -29,10 +29,19 @@ export class Xtb extends Serializer {
     // xml nodes to i18n nodes
     const i18nNodesByMsgId: {[msgId: string]: i18n.Node[]} = {};
     const converter = new XmlToI18n();
+
+    // Because we should be able to load xtb files that rely on features not supported by angular,
+    // we need to delay the conversion of html to i18n nodes so that non angular messages are not
+    // converted
     Object.keys(mlNodesByMsgId).forEach(msgId => {
-      const {i18nNodes, errors: e} = converter.convert(mlNodesByMsgId[msgId]);
-      errors.push(...e);
-      i18nNodesByMsgId[msgId] = i18nNodes;
+      const valueFn = function() {
+        const {i18nNodes, errors} = converter.convert(mlNodesByMsgId[msgId]);
+        if (errors.length) {
+          throw new Error(`xtb parse errors:\n${errors.join('\n')}`);
+        }
+        return i18nNodes;
+      };
+      createLazyProperty(i18nNodesByMsgId, msgId, valueFn);
     });
 
     if (errors.length) {
@@ -49,6 +58,19 @@ export class Xtb extends Serializer {
   }
 }
 
+function createLazyProperty(messages: any, id: string, valueFn: () => any) {
+  Object.defineProperty(messages, id, {
+    configurable: true,
+    enumerable: true,
+    get: function() {
+      const value = valueFn();
+      Object.defineProperty(messages, id, {enumerable: true, value});
+      return value;
+    },
+    set: _ => { throw new Error('Could not overwrite an XTB translation'); },
+  });
+}
+
 // Extract messages as xml nodes from the xtb file
 class XtbParser implements ml.Visitor {
   private _bundleDepth: number;

modules/@angular/compiler/test/i18n/serializers/xtb_spec.ts

@@ -9,8 +9,10 @@
 import {escapeRegExp} from '@angular/core/src/facade/lang';
 
 import {serializeNodes} from '../../../src/i18n/digest';
+import * as i18n from '../../../src/i18n/i18n_ast';
 import {Xtb} from '../../../src/i18n/serializers/xtb';
 
+
 export function main(): void {
   describe('XTB serializer', () => {
     const serializer = new Xtb();
@@ -100,6 +102,25 @@ export function main(): void {
     });
 
     describe('errors', () => {
+      it('should be able to parse non-angular xtb files without error', () => {
+        const XTB = `<?xml version="1.0" encoding="UTF-8" ?>
+<translationbundle>
+  <translation id="angular">is great</translation>
+  <translation id="non angular">is <invalid>less</invalid> great</translation>
+</translationbundle>`;
+
+        // Invalid messages should not cause the parser to throw
+        let i18nNodesByMsgId: {[id: string]: i18n.Node[]};
+        expect(() => { i18nNodesByMsgId = serializer.load(XTB, 'url'); }).not.toThrow();
+
+        expect(Object.keys(i18nNodesByMsgId).length).toEqual(2);
+        expect(serializeNodes(i18nNodesByMsgId['angular']).join('')).toEqual('is great');
+        // Messages that contain unsupported feature should throw on access
+        expect(() => {
+          const read = i18nNodesByMsgId['non angular'];
+        }).toThrowError(/xtb parse errors/);
+      });
+
       it('should throw on nested <translationbundle>', () => {
         const XTB =
             '<translationbundle><translationbundle></translationbundle></translationbundle>';