fix(@ngtools/webpack): don't elide imports for type references that are needed for decorator metadata

When `emitDecoratorMetadata` is set to true we don't elide type references imports that are used for decorated nodes.

Fixes #16808

Author: alan-agius4

packages/ngtools/webpack/src/transformers/ast_helpers.ts

@@ -50,13 +50,14 @@ export function getLastNode(sourceFile: ts.SourceFile): ts.Node | null {
 // Test transform helpers.
 const basePath = '/project/src/';
 const fileName = basePath + 'test-file.ts';
+const typeScriptLibFiles = loadTypeScriptLibFiles();
 const tsLibFiles = loadTsLibFiles();
 
 export function createTypescriptContext(
   content: string,
   additionalFiles?: Record<string, string>,
   useLibs = false,
-  importHelpers = true,
+  extraCompilerOptions: ts.CompilerOptions = {},
 ) {
   // Set compiler options.
   const compilerOptions: ts.CompilerOptions = {
@@ -68,7 +69,9 @@ export function createTypescriptContext(
     target: ts.ScriptTarget.ESNext,
     skipLibCheck: true,
     sourceMap: false,
-    importHelpers,
+    importHelpers: true,
+    experimentalDecorators: true,
+    ...extraCompilerOptions,
   };
 
   // Create compiler host.
@@ -86,11 +89,17 @@ export function createTypescriptContext(
     // Write the default libs.
     // These are needed for tests that use import(), because it relies on a Promise being there.
     const compilerLibFolder = dirname(compilerHost.getDefaultLibFileName(compilerOptions));
-    for (const [k, v] of Object.entries(tsLibFiles)) {
+    for (const [k, v] of Object.entries(typeScriptLibFiles)) {
       compilerHost.writeFile(join(compilerLibFolder, k), v, false);
     }
   }
 
+  if (compilerOptions.importHelpers) {
+    for (const [k, v] of Object.entries(tsLibFiles)) {
+      compilerHost.writeFile(k, v, false);
+    }
+  }
+
   if (additionalFiles) {
     for (const key in additionalFiles) {
       compilerHost.writeFile(basePath + key, additionalFiles[key], false);
@@ -108,8 +117,7 @@ export function transformTypescript(
   transformers: ts.TransformerFactory<ts.SourceFile>[],
   program?: ts.Program,
   compilerHost?: WebpackCompilerHost,
-) {
-
+): string | undefined {
   // Use given context or create a new one.
   if (content !== undefined) {
     const typescriptContext = createTypescriptContext(content);
@@ -137,18 +145,29 @@ export function transformTypescript(
   return compilerHost.readFile(fileName.replace(/\.tsx?$/, '.js'));
 }
 
-function loadTsLibFiles() {
+function loadTypeScriptLibFiles(): Record<string, string> {
   const libFolderPath = dirname(require.resolve('typescript/lib/lib.d.ts'));
   const libFolderFiles = readdirSync(libFolderPath);
   const libFileNames = libFolderFiles.filter(f => f.startsWith('lib.') && f.endsWith('.d.ts'));
 
   // Return a map of the lib names to their content.
-  return libFileNames.reduce(
-    (map, f) => {
-      map[f] = readFileSync(join(libFolderPath, f), 'utf-8');
+  const libs: Record<string, string> = {};
+  for (const f of libFileNames) {
+    libs[f] = readFileSync(join(libFolderPath, f), 'utf-8');
+  }
+
+  return libs;
+}
+
+function loadTsLibFiles(): Record<string, string> {
+  const libFolderPath = dirname(require.resolve('tslib/package.json'));
+  const libFolderFiles = readdirSync(libFolderPath);
+
+  // Return a map of the lib names to their content.
+  const libs: Record<string, string> = {};
+  for (const f of libFolderFiles) {
+    libs[join('node_modules/tslib', f)] = readFileSync(join(libFolderPath, f), 'utf-8');
+  }
 
-      return map;
-    },
-    {} as { [k: string]: string },
-  );
+  return libs;
 }

packages/ngtools/webpack/src/transformers/elide_imports.ts

@@ -19,6 +19,7 @@ export function elideImports(
   sourceFile: ts.SourceFile,
   removedNodes: ts.Node[],
   getTypeChecker: () => ts.TypeChecker,
+  compilerOptions: ts.CompilerOptions,
 ): TransformOperation[] {
   const ops: TransformOperation[] = [];
 
@@ -33,8 +34,8 @@ export function elideImports(
   const imports: ts.ImportDeclaration[] = [];
 
   ts.forEachChild(sourceFile, function visit(node) {
-    // Skip type references and removed nodes. We consider both unused.
-    if (node.kind == ts.SyntaxKind.TypeReference || removedNodes.includes(node)) {
+    // Skip removed nodes.
+    if (removedNodes.includes(node)) {
       return;
     }
 
@@ -46,17 +47,48 @@ export function elideImports(
     }
 
     let symbol: ts.Symbol | undefined;
+    if (ts.isTypeReferenceNode(node)) {
+      if (!compilerOptions.emitDecoratorMetadata) {
+        // Skip and mark as unused if emitDecoratorMetadata is disabled.
+        return;
+      }
 
-    switch (node.kind) {
-      case ts.SyntaxKind.Identifier:
+      const parent = node.parent;
+      let isTypeReferenceForDecoratoredNode = false;
+
+      switch (parent.kind) {
+        case ts.SyntaxKind.GetAccessor:
+        case ts.SyntaxKind.PropertyDeclaration:
+        case ts.SyntaxKind.MethodDeclaration:
+          isTypeReferenceForDecoratoredNode = !!parent.decorators?.length;
+          break;
+        case ts.SyntaxKind.Parameter:
+          // - A constructor parameter can be decorated or the class itself is decorated.
+          // - The parent of the parameter is decorated example a method declaration or a set accessor.
+          // In all cases we need the type reference not to be elided.
+          isTypeReferenceForDecoratoredNode = !!(parent.decorators?.length ||
+            (ts.isSetAccessor(parent.parent) && !!parent.parent.decorators?.length) ||
+            (ts.isConstructorDeclaration(parent.parent) && !!parent.parent.parent.decorators?.length));
+          break;
+      }
+      if (isTypeReferenceForDecoratoredNode) {
         symbol = typeChecker.getSymbolAtLocation(node);
-        break;
-      case ts.SyntaxKind.ExportSpecifier:
-        symbol = typeChecker.getExportSpecifierLocalTargetSymbol(node as ts.ExportSpecifier);
-        break;
-      case ts.SyntaxKind.ShorthandPropertyAssignment:
-        symbol = typeChecker.getShorthandAssignmentValueSymbol(node);
-        break;
+      } else {
+        // If type reference is not for Decorator skip and marked as unused.
+        return;
+      }
+    } else {
+      switch (node.kind) {
+        case ts.SyntaxKind.Identifier:
+          symbol = typeChecker.getSymbolAtLocation(node);
+          break;
+        case ts.SyntaxKind.ExportSpecifier:
+          symbol = typeChecker.getExportSpecifierLocalTargetSymbol(node as ts.ExportSpecifier);
+          break;
+        case ts.SyntaxKind.ShorthandPropertyAssignment:
+          symbol = typeChecker.getShorthandAssignmentValueSymbol(node);
+          break;
+      }
     }
 
     if (symbol) {