From 6a19c217eaebf9c0bffba8482545efc375fd2a8a Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Mon, 13 Jan 2025 20:06:33 -0500
Subject: [PATCH] fix(@angular/build): warn when using both `isolatedModules`
 and `emitDecoratorMetadata`

If both the `isolatedModules` and `emitDecoratorMetadata` Typescript
options are enabled within a project, a warning will now be issued
explaining that not all metadata may be emitting for each decorator.
Isolated modules may not have access to non-local type information
that would otherwise be needed for complete metadata emit.

The `emitDecoratorMetadata` option is not required by Angular and can cause
runtime errors due to its underlying implementation when used with
ES2015+ output. The option is only compatible with the experimental
decorators and cannot be used with standard decorators. New Angular
projects also do not enable this option.

(cherry picked from commit 61e8185ab0081ca01a849055b3050f2456af8c23)
---
 .../src/tools/esbuild/angular/compiler-plugin.ts   | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/packages/angular/build/src/tools/esbuild/angular/compiler-plugin.ts b/packages/angular/build/src/tools/esbuild/angular/compiler-plugin.ts
index 740c2d119b5a..798adc090f8e 100644
--- a/packages/angular/build/src/tools/esbuild/angular/compiler-plugin.ts
+++ b/packages/angular/build/src/tools/esbuild/angular/compiler-plugin.ts
@@ -689,6 +689,20 @@ function createCompilerOptionsTransformer(
       });
     }
 
+    if (compilerOptions.isolatedModules && compilerOptions.emitDecoratorMetadata) {
+      setupWarnings?.push({
+        text: `TypeScript compiler option 'isolatedModules' may prevent the 'emitDecoratorMetadata' option from emitting all metadata.`,
+        location: null,
+        notes: [
+          {
+            text:
+              `The 'emitDecoratorMetadata' option is not required by Angular` +
+              'and can be removed if not explictly required by the project.',
+          },
+        ],
+      });
+    }
+
     // Synchronize custom resolve conditions.
     // Set if using the supported bundler resolution mode (bundler is the default in new projects)
     if (compilerOptions.moduleResolution === 100 /* ModuleResolutionKind.Bundler */) {