From 0abae8b3b179641e555adcc58f9edfbf3716abd3 Mon Sep 17 00:00:00 2001
From: Maruthan G <maruthang4@gmail.com>
Date: Sat, 28 Mar 2026 02:17:52 +0530
Subject: [PATCH] fix(@ngtools/webpack): emit diagnostic for unsupported
 conditional templateUrl expressions

Fixes #27611
---
 .../src/transformers/replace_resources.ts     | 15 ++++++-
 .../transformers/replace_resources_spec.ts    | 42 +++++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/packages/ngtools/webpack/src/transformers/replace_resources.ts b/packages/ngtools/webpack/src/transformers/replace_resources.ts
index 9197ae3afd59..5283d1634130 100644
--- a/packages/ngtools/webpack/src/transformers/replace_resources.ts
+++ b/packages/ngtools/webpack/src/transformers/replace_resources.ts
@@ -41,6 +41,7 @@ export function replaceResources(
                 resourceImportDeclarations,
                 moduleKind,
                 inlineStyleFileExtension,
+                node,
               ),
             ),
             ...(ts.getModifiers(node) ?? []),
@@ -87,6 +88,7 @@ function visitDecorator(
   resourceImportDeclarations: ts.ImportDeclaration[],
   moduleKind?: ts.ModuleKind,
   inlineStyleFileExtension?: string,
+  classDeclaration?: ts.ClassDeclaration,
 ): ts.Decorator {
   if (!isComponentDecorator(node, typeChecker)) {
     return node;
@@ -106,6 +108,8 @@ function visitDecorator(
   const objectExpression = args[0];
   const styleReplacements: ts.Expression[] = [];
 
+  const className = classDeclaration?.name?.text ?? 'Unknown';
+
   // visit all properties
   let properties = ts.visitNodes(objectExpression.properties, (node) =>
     ts.isObjectLiteralElementLike(node)
@@ -116,6 +120,7 @@ function visitDecorator(
           resourceImportDeclarations,
           moduleKind,
           inlineStyleFileExtension,
+          className,
         )
       : node,
   ) as ts.NodeArray<ts.ObjectLiteralElementLike>;
@@ -148,6 +153,7 @@ function visitComponentMetadata(
   resourceImportDeclarations: ts.ImportDeclaration[],
   moduleKind: ts.ModuleKind = ts.ModuleKind.ES2015,
   inlineStyleFileExtension?: string,
+  className?: string,
 ): ts.ObjectLiteralElementLike | undefined {
   if (!ts.isPropertyAssignment(node) || ts.isComputedPropertyName(node.name)) {
     return node;
@@ -161,7 +167,14 @@ function visitComponentMetadata(
     case 'templateUrl': {
       const url = getResourceUrl(node.initializer);
       if (!url) {
-        return node;
+        const sourceFile = node.getSourceFile();
+        const { line } = sourceFile.getLineAndCharacterOfPosition(node.initializer.getStart());
+
+        throw new Error(
+          `Component '${className}' in '${sourceFile.fileName}' contains a non-string literal ` +
+            `'templateUrl' value at line ${line + 1}. The 'templateUrl' property must be a ` +
+            `string literal. Expressions, variables, or other dynamic values are not supported.`,
+        );
       }
 
       const importName = createResourceImport(
diff --git a/packages/ngtools/webpack/src/transformers/replace_resources_spec.ts b/packages/ngtools/webpack/src/transformers/replace_resources_spec.ts
index e0be8e4ebb03..5a140d04b183 100644
--- a/packages/ngtools/webpack/src/transformers/replace_resources_spec.ts
+++ b/packages/ngtools/webpack/src/transformers/replace_resources_spec.ts
@@ -469,4 +469,46 @@ describe('find_resources', () => {
     const result = transform(input, false);
     expect(tags.oneLine`${result}`).toEqual(tags.oneLine`${output}`);
   });
+
+  it('should throw an error when templateUrl is a conditional expression', () => {
+    const input = tags.stripIndent`
+        import { Component } from '@angular/core';
+
+        @Component({
+          selector: 'app-root',
+          templateUrl: true === true
+            ? './app.component.html'
+            : './app.component.copy.html',
+          styleUrls: ['./app.component.css', './app.component.2.css']
+        })
+        export class AppComponent {
+          title = 'app';
+        }
+      `;
+
+    expect(() => transform(input)).toThrowError(
+      /Component 'AppComponent'.*contains a non-string literal 'templateUrl' value/,
+    );
+  });
+
+  it('should throw an error when templateUrl is a variable reference', () => {
+    const input = tags.stripIndent`
+        import { Component } from '@angular/core';
+
+        const myTemplate = './app.component.html';
+
+        @Component({
+          selector: 'app-root',
+          templateUrl: myTemplate,
+          styleUrls: ['./app.component.css']
+        })
+        export class AppComponent {
+          title = 'app';
+        }
+      `;
+
+    expect(() => transform(input)).toThrowError(
+      /Component 'AppComponent'.*contains a non-string literal 'templateUrl' value/,
+    );
+  });
 });