fix(@angular-devkit/build-optimizer): don't mark tslib helpers which are suffixed with $ and a number as pure (#15451)

Closes #15392

Author: alan-agius4

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

@@ -100,7 +100,7 @@ describe('build-optimizer', () => {
       expect(boOutput.emitSkipped).toEqual(false);
     });
 
-    it(`doesn't add pure comments to tslib helpers`, () => {
+    it('should not add pure comments to tslib helpers', () => {
       const input = tags.stripIndent`
         class LanguageState {
         }
@@ -138,6 +138,44 @@ describe('build-optimizer', () => {
       expect(boOutput.emitSkipped).toEqual(false);
     });
 
+    it('should not add pure comments to tslib helpers with $ and number suffix', () => {
+      const input = tags.stripIndent`
+        class LanguageState {
+        }
+
+        LanguageState.ctorParameters = () => [
+            { type: TranslateService },
+            { type: undefined, decorators: [{ type: Inject, args: [LANGUAGE_CONFIG,] }] }
+        ];
+
+        __decorate$1([
+            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$1([
+              Action(CheckLanguage),
+              __metadata("design:type", Function),
+              __metadata("design:paramtypes", [Object]),
+              __metadata("design:returntype", void 0)
+          ], LanguageState.prototype, "checkLanguage", null);
+          return LanguageState;
+       })();
+      `;
+
+      const boOutput = buildOptimizer({ content: input, isSideEffectFree: true });
+      expect(tags.oneLine`${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

@@ -50,3 +50,23 @@ export function hasPureComment(node: ts.Node): boolean {
 export function isHelperName(name: string): boolean {
   return tslibHelpers.has(name);
 }
+
+/**
+ * In FESM's when not using `importHelpers` there might be multiple in the same file.
+  @example
+  ```
+  var __decorate$1 = '';
+  var __decorate$2 = '';
+  ```
+ * @returns Helper name without the '$' and number suffix or `undefined` if it's not a helper.
+ */
+export function getCleanHelperName(name: string): string | undefined {
+  const parts = name.split('$');
+  const cleanName = parts[0];
+
+  if (parts.length > 2 || (parts.length === 2 && isNaN(+parts[1]))) {
+    return undefined;
+  }
+
+  return isHelperName(cleanName) ? cleanName : undefined;
+}

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

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import * as ts from 'typescript';
-import { isHelperName } from '../helpers/ast-utils';
+import { getCleanHelperName } from '../helpers/ast-utils';
 
 /**
  * @deprecated From 0.9.0
@@ -35,14 +35,9 @@ export function getImportTslibTransformer(): ts.TransformerFactory<ts.SourceFile
 
           if (declarations.length === 1 && ts.isIdentifier(declarations[0].name)) {
             const name = declarations[0].name.text;
+            const helperName = getCleanHelperName(name);
 
-            // In FESM's when not using importHelpers there might be nultiple in the same file.
-            // Example:
-            // var __decorate$1 = '';
-            // var __decorate$2 = '';
-            const helperName = name.split(/\$\d+$/)[0];
-
-            if (isHelperName(helperName)) {
+            if (helperName) {
               // TODO: maybe add a few more checks, like checking the first part of the assignment.
               const alias = name === helperName ? undefined : name;
               const tslibImport = createTslibImport(helperName, alias, useRequire);

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, isHelperName } from '../helpers/ast-utils';
+import { addPureComment, getCleanHelperName, hasPureComment } from '../helpers/ast-utils';
 
 export function getPrefixFunctionsTransformer(): ts.TransformerFactory<ts.SourceFile> {
   return (context: ts.TransformationContext): ts.Transformer<ts.SourceFile> => {
@@ -77,7 +77,7 @@ export function findTopLevelFunctions(parentNode: ts.Node): Set<ts.Node> {
       } else if (ts.isCallExpression(innerNode)) {
         let expression: ts.Expression = innerNode.expression;
 
-        if (ts.isIdentifier(expression) && isHelperName(expression.text)) {
+        if (ts.isIdentifier(expression) && getCleanHelperName(expression.text)) {
           return;
         }