fix(@angular-devkit/build-angular): clear diagnostic cache when external templates change with esbuild builders

To prevent stale Angular template diagnostics from persisting in watch mode (including `ng serve`), the template
diagnostic cache will now be invalidated based on the set of changed external template files. This ensures that
the Angular AOT compiler will analyze the template again during the rebuild and clear any fixed errors.

Author: clydin

packages/angular_devkit/build_angular/src/tools/esbuild/angular/compilation/aot-compilation.ts

@@ -78,7 +78,7 @@ export class AotCompilation extends AngularCompilation {
     let usingBuildInfo = false;
     if (!oldProgram) {
       oldProgram = ts.readBuilderProgram(compilerOptions, host);
-      usingBuildInfo = true;
+      usingBuildInfo = !!oldProgram;
     }
 
     const typeScriptProgram = ts.createEmitAndSemanticDiagnosticsBuilderProgram(
@@ -93,6 +93,25 @@ export class AotCompilation extends AngularCompilation {
       findAffectedFiles(typeScriptProgram, angularCompiler, usingBuildInfo),
     );
 
+    // Get all files referenced in the TypeScript/Angular program including component resources
+    const referencedFiles = typeScriptProgram
+      .getSourceFiles()
+      .filter((sourceFile) => !angularCompiler.ignoreForEmit.has(sourceFile))
+      .flatMap((sourceFile) => {
+        const resourceDependencies = angularCompiler.getResourceDependencies(sourceFile);
+
+        // Also invalidate Angular diagnostics for a source file if component resources are modified
+        if (this.#state && hostOptions.modifiedFiles?.size) {
+          for (const resourceDependency of resourceDependencies) {
+            if (hostOptions.modifiedFiles.has(resourceDependency)) {
+              this.#state.diagnosticCache.delete(sourceFile);
+            }
+          }
+        }
+
+        return [sourceFile.fileName, ...resourceDependencies];
+      });
+
     this.#state = new AngularCompilationState(
       angularProgram,
       host,
@@ -103,14 +122,6 @@ export class AotCompilation extends AngularCompilation {
       this.#state?.diagnosticCache,
     );
 
-    const referencedFiles = typeScriptProgram
-      .getSourceFiles()
-      .filter((sourceFile) => !angularCompiler.ignoreForEmit.has(sourceFile))
-      .flatMap((sourceFile) => [
-        sourceFile.fileName,
-        ...angularCompiler.getResourceDependencies(sourceFile),
-      ]);
-
     return { affectedFiles, compilerOptions, referencedFiles };
   }