fix(@angular-devkit/build-optimizer): don't add pure comments to tslib helpers (#15303)

Closes #15301

Author: alan-agius4

packages/angular_devkit/build_optimizer/BUILD

@@ -28,6 +28,7 @@ ts_library(
         "@npm//@types/node",
         "@npm//@types/webpack",
         "@npm//source-map",
+        "@npm//tslib",
         "@npm//typescript",
     ],
 )

packages/angular_devkit/build_optimizer/package.json

@@ -11,6 +11,7 @@
   "dependencies": {
     "loader-utils": "1.2.3",
     "source-map": "0.7.3",
+    "tslib": "1.10.0",
     "typescript": "3.5.3",
     "webpack-sources": "1.4.3"
   }

packages/angular_devkit/build_optimizer/src/build-optimizer/build-optimizer_spec.ts

@@ -100,6 +100,44 @@ describe('build-optimizer', () => {
       expect(boOutput.emitSkipped).toEqual(false);
     });
 
+    it(`doesn't add pure comments to tslib helpers`, () => {
+      const input = tags.stripIndent`
+        class LanguageState {
+        }
+
+        LanguageState.ctorParameters = () => [
+            { type: TranslateService },
+            { type: undefined, decorators: [{ type: Inject, args: [LANGUAGE_CONFIG,] }] }
+        ];
+
+        __decorate([
+            Action(CheckLanguage),
+            __metadata("design:type", Function),
+            __metadata("design:paramtypes", [Object]),
+            __metadata("design:returntype", void 0)
+        ], LanguageState.prototype, "checkLanguage", null);
+      `;
+
+      const output = tags.oneLine`
+        let LanguageState = /*@__PURE__*/ (() => {
+          class LanguageState {
+          }
+
+          __decorate([
+              Action(CheckLanguage),
+              __metadata("design:type", Function),
+              __metadata("design:paramtypes", [Object]),
+              __metadata("design:returntype", void 0)
+          ], LanguageState.prototype, "checkLanguage", null);
+          return LanguageState;
+       })();
+      `;
+
+      const boOutput = buildOptimizer({ content: input, isSideEffectFree: true });
+      expect(tags.oneLine`${boOutput.content}`).toEqual(output);
+      expect(boOutput.emitSkipped).toEqual(false);
+    });
+
     it('should not wrap classes which had all static properties dropped in IIFE', () => {
       const classDeclaration = tags.oneLine`
         import { Injectable } from '@angular/core';

packages/angular_devkit/build_optimizer/src/helpers/ast-utils.ts

@@ -5,10 +5,15 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
+import * as tslib from 'tslib';
 import * as ts from 'typescript';
 
 const pureFunctionComment = '@__PURE__';
 
+// We include only exports that start with '__' because tslib helpers
+// all start with a suffix of two underscores.
+const tslibHelpers = new Set<string>(Object.keys(tslib).filter(h => h.startsWith('__')));
+
 // Find all nodes from the AST in the subtree of node of SyntaxKind kind.
 export function collectDeepNodes<T extends ts.Node>(node: ts.Node, kind: ts.SyntaxKind): T[] {
   const nodes: T[] = [];
@@ -41,3 +46,7 @@ export function hasPureComment(node: ts.Node): boolean {
 
   return !!leadingComment && leadingComment.some(comment => comment.text === pureFunctionComment);
 }
+
+export function isHelperName(name: string): boolean {
+  return tslibHelpers.has(name);
+}

packages/angular_devkit/build_optimizer/src/transforms/import-tslib.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import * as ts from 'typescript';
+import { isHelperName } from '../helpers/ast-utils';
 
 /**
  * @deprecated From 0.9.0
@@ -89,15 +90,3 @@ function createTslibImport(
     return newNode;
   }
 }
-
-function isHelperName(name: string): boolean {
-  // TODO: there are more helpers than these, should we replace them all?
-  const tsHelpers = [
-    '__extends',
-    '__decorate',
-    '__metadata',
-    '__param',
-  ];
-
-  return tsHelpers.indexOf(name) !== -1;
-}

packages/angular_devkit/build_optimizer/src/transforms/prefix-functions.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import * as ts from 'typescript';
-import { addPureComment, hasPureComment } from '../helpers/ast-utils';
+import { addPureComment, hasPureComment, isHelperName } from '../helpers/ast-utils';
 
 export function getPrefixFunctionsTransformer(): ts.TransformerFactory<ts.SourceFile> {
   return (context: ts.TransformationContext): ts.Transformer<ts.SourceFile> => {
@@ -44,10 +44,8 @@ export function findTopLevelFunctions(parentNode: ts.Node): Set<ts.Node> {
     // need to mark function calls inside them as pure.
     // Class static initializers in ES2015 are an exception we don't cover. They would need similar
     // processing as enums to prevent property setting from causing the class to be retained.
-    if (ts.isFunctionDeclaration(node)
-      || ts.isFunctionExpression(node)
-      || ts.isClassDeclaration(node)
-      || ts.isClassExpression(node)
+    if (ts.isFunctionLike(node)
+      || ts.isClassLike(node)
       || ts.isArrowFunction(node)
       || ts.isMethodDeclaration(node)
     ) {
@@ -78,9 +76,15 @@ export function findTopLevelFunctions(parentNode: ts.Node): Set<ts.Node> {
         topLevelFunctions.add(node);
       } else if (ts.isCallExpression(innerNode)) {
         let expression: ts.Expression = innerNode.expression;
+
+        if (ts.isIdentifier(expression) && isHelperName(expression.text)) {
+          return;
+        }
+
         while (expression && ts.isParenthesizedExpression(expression)) {
           expression = expression.expression;
         }
+
         if (expression) {
           if (ts.isFunctionExpression(expression)) {
             // Skip IIFE's with arguments

packages/angular_devkit/build_optimizer/src/transforms/prefix-functions_spec.ts

@@ -186,4 +186,28 @@ describe('prefix-functions', () => {
 
     expect(tags.oneLine`${transform(input)}`).toEqual(tags.oneLine`${output}`);
   });
+
+  it(`doesn't add pure comments to tslib helpers`, () => {
+    const input = tags.stripIndent`
+    class LanguageState {
+
+    }
+
+    LanguageState.ctorParameters = () => [
+        { type: TranslateService },
+        { type: undefined, decorators: [{ type: Inject, args: [LANGUAGE_CONFIG,] }] }
+    ];
+
+    __decorate([
+        Action(CheckLanguage),
+        __metadata("design:type", Function),
+        __metadata("design:paramtypes", [Object]),
+        __metadata("design:returntype", void 0)
+    ], LanguageState.prototype, "checkLanguage", null);
+    `;
+
+    const output = input;
+
+    expect(tags.oneLine`${transform(input)}`).toEqual(tags.oneLine`${output}`);
+  });
 });