From ab854c3bffafc1b120b62385153932054e2c6c43 Mon Sep 17 00:00:00 2001
From: Alan Agius <alan.agius4@gmail.com>
Date: Fri, 7 Jun 2019 00:04:36 +0200
Subject: [PATCH] fix(@schematics/angular): enable tsc `downlevelIteration`

We by default now use ES2015. Users can use ES2015 iterations however the ES5 build will fail.

Fixes #14697
---
 .../update-8/differential-loading.ts          |  9 ++++++++
 .../update-8/differential-loading_spec.ts     | 23 +++++++++++++++++++
 .../workspace/files/tsconfig.json.template    |  3 ++-
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/packages/schematics/angular/migrations/update-8/differential-loading.ts b/packages/schematics/angular/migrations/update-8/differential-loading.ts
index 41408e6b18a3..dd943583aced 100644
--- a/packages/schematics/angular/migrations/update-8/differential-loading.ts
+++ b/packages/schematics/angular/migrations/update-8/differential-loading.ts
@@ -131,7 +131,16 @@ function updateTsConfig(tree: Tree, tsConfigPath: string): void {
   if (isExtendedConfig) {
     removePropertyInAstObject(recorder, compilerOptions, 'target');
     removePropertyInAstObject(recorder, compilerOptions, 'module');
+    removePropertyInAstObject(recorder, compilerOptions, 'downlevelIteration');
   } else {
+    const downlevelIteration = findPropertyInAstObject(compilerOptions, 'downlevelIteration');
+    if (!downlevelIteration) {
+      insertPropertyInAstObjectInOrder(recorder, compilerOptions, 'downlevelIteration', true, 4);
+    } else if (!downlevelIteration.value) {
+      const { start, end } = downlevelIteration;
+      recorder.remove(start.offset, end.offset - start.offset);
+      recorder.insertLeft(start.offset, 'true');
+    }
     const scriptTarget = findPropertyInAstObject(compilerOptions, 'target');
     if (!scriptTarget) {
       insertPropertyInAstObjectInOrder(recorder, compilerOptions, 'target', 'es2015', 4);
diff --git a/packages/schematics/angular/migrations/update-8/differential-loading_spec.ts b/packages/schematics/angular/migrations/update-8/differential-loading_spec.ts
index c546af8d346d..57fc7cd2f9df 100644
--- a/packages/schematics/angular/migrations/update-8/differential-loading_spec.ts
+++ b/packages/schematics/angular/migrations/update-8/differential-loading_spec.ts
@@ -80,6 +80,29 @@ describe('Migration to version 8', () => {
       expect(module).toBe('esnext');
     });
 
+    it(`should create 'downlevelIteration' property when doesn't exists`, () => {
+      const tree2 = schematicRunner.runSchematic('migration-07', {}, tree.branch());
+      const compilerOptions = {
+        ...oldTsConfig.compilerOptions,
+      };
+
+      tree.overwrite(tsConfigPath, JSON.stringify({ compilerOptions }, null, 2));
+      const { downlevelIteration } = JSON.parse(tree2.readContent(tsConfigPath)).compilerOptions;
+      expect(downlevelIteration).toBe(true);
+    });
+
+    it(`should update 'downlevelIteration' to true when it's false`, () => {
+      const tree2 = schematicRunner.runSchematic('migration-07', {}, tree.branch());
+      const compilerOptions = {
+        ...oldTsConfig.compilerOptions,
+        downlevelIteration: false,
+      };
+
+      tree.overwrite(tsConfigPath, JSON.stringify({ compilerOptions }, null, 2));
+      const { downlevelIteration } = JSON.parse(tree2.readContent(tsConfigPath)).compilerOptions;
+      expect(downlevelIteration).toBe(true);
+    });
+
     it(`should create browserslist file if it doesn't exist`, () => {
       tree.delete('/browserslist');
       const tree2 = schematicRunner.runSchematic('migration-07', {}, tree.branch());
diff --git a/packages/schematics/angular/workspace/files/tsconfig.json.template b/packages/schematics/angular/workspace/files/tsconfig.json.template
index 1e35a04fa981..a4df54fff629 100644
--- a/packages/schematics/angular/workspace/files/tsconfig.json.template
+++ b/packages/schematics/angular/workspace/files/tsconfig.json.template
@@ -5,9 +5,10 @@
     "outDir": "./dist/out-tsc",
     "sourceMap": true,
     "declaration": false,
+    "downlevelIteration": true,
+    "experimentalDecorators": true,
     "module": "esnext",
     "moduleResolution": "node",
-    "experimentalDecorators": true,
     "importHelpers": true,
     "target": "es2015",
     "typeRoots": [