feat(@angular-devkit/build-angular): expose legacy-migrate message format

We recently added a new message format called `legacy-extract` that is used to migrate between
legacy and canonical message IDs (see angular/angular#41026).

These changes expose the new format in `extract-i18n`.

Author: crisbeto

packages/angular_devkit/build_angular/src/extract-i18n/index.ts

@@ -13,6 +13,7 @@ import {
 import { BuildResult, runWebpack } from '@angular-devkit/build-webpack';
 import { JsonObject } from '@angular-devkit/core';
 import type { ɵParsedMessage as LocalizeMessage } from '@angular/localize';
+import type { Diagnostics } from '@angular/localize/src/tools/src/diagnostics';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as webpack from 'webpack';
@@ -38,6 +39,7 @@ function getI18nOutfile(format: string | undefined) {
     case 'xliff2':
       return 'messages.xlf';
     case 'json':
+    case 'legacy-migrate':
       return 'messages.json';
     case 'arb':
       return 'messages.arb';
@@ -46,7 +48,7 @@ function getI18nOutfile(format: string | undefined) {
   }
 }
 
-async function getSerializer(format: Format, sourceLocale: string, basePath: string, useLegacyIds: boolean) {
+async function getSerializer(format: Format, sourceLocale: string, basePath: string, useLegacyIds: boolean, diagnostics: Diagnostics) {
   switch (format) {
     case Format.Xmb:
       const { XmbTranslationSerializer } =
@@ -73,8 +75,12 @@ async function getSerializer(format: Format, sourceLocale: string, basePath: str
       const { SimpleJsonTranslationSerializer } =
         await import('@angular/localize/src/tools/src/extract/translation_files/json_translation_serializer');
 
-      // tslint:disable-next-line: no-any
       return new SimpleJsonTranslationSerializer(sourceLocale);
+    case Format.LegacyMigrate:
+      const { LegacyMessageIdMigrationSerializer } =
+        await import('@angular/localize/src/tools/src/extract/translation_files/legacy_message_id_migration_serializer');
+
+      return new LegacyMessageIdMigrationSerializer(diagnostics);
     case Format.Arb:
       const { ArbTranslationSerializer } =
         await import('@angular/localize/src/tools/src/extract/translation_files/arb_translation_serializer');
@@ -114,6 +120,9 @@ function normalizeFormatOption(options: ExtractI18nBuilderOptions) {
     case Format.Arb:
       format = Format.Arb;
       break;
+    case Format.LegacyMigrate:
+      format = Format.LegacyMigrate;
+      break;
     case undefined:
       format = Format.Xlf;
       break;
@@ -311,6 +320,7 @@ export async function execute(
     i18n.sourceLocale,
     basePath,
     useLegacyIds,
+    diagnostics,
   );
   const content = serializer.serialize(ivyMessages);
 

packages/angular_devkit/build_angular/src/extract-i18n/schema.json

@@ -21,7 +21,8 @@
         "xlf2",
         "xliff2",
         "json",
-        "arb"
+        "arb",
+        "legacy-migrate"
       ]
     },
     "i18nFormat": {
@@ -37,7 +38,8 @@
         "xlf2",
         "xliff2",
         "json",
-        "arb"
+        "arb",
+        "legacy-migrate"
       ]
     },
     "i18nLocale": {