refactor(compiler-cli): add a helper to generate error `LOCAL_COMPILA…

…TION_UNRESOLVED_CONST` in common scenarios (#54230)

A helper `validateLocalCompilationUnresolvedConst` is added to encapsulate a common pattern which leads to the error `LOCAL_COMPILATION_UNRESOLVED_CONST`.

PR Close #54230

packages/compiler-cli/src/ngtsc/annotations/common/src/diagnostics.ts

@@ -18,6 +18,7 @@ import {identifierOfNode, isFromDtsFile} from '../../../util/src/typescript';
 
 import {InjectableClassRegistry} from './injectable_registry';
 import {isAbstractClassDeclaration, readBaseClass} from './util';
+import { CompilationMode } from '../../../transform';
 
 
 /**
@@ -403,3 +404,19 @@ function getInheritedUndecoratedCtorDiagnostic(
               baseNeedsDecorator} decorator ` +
           `to ${baseClassName}, or add an explicit constructor to ${node.name.text}.`);
 }
+
+/**
+ * Throws `FatalDiagnosticError` with error code `LOCAL_COMPILATION_UNRESOLVED_CONST` 
+ * if the compilation mode is local and the value is not resolved due to being imported
+ * from external files. This is a common scenario for errors in local compilation mode,
+ * and so this helper can be used to quickly generate the relevant errors.
+ */
+export function assertLocalCompilationUnresolvedConst(compilationMode: CompilationMode, value: ResolvedValue, nodeToHighlight: ts.Node, errorMessage: string): void {
+  if (compilationMode === CompilationMode.LOCAL && value instanceof DynamicValue &&
+    value.isFromUnknownIdentifier()) {
+    throw new FatalDiagnosticError(
+        ErrorCode.LOCAL_COMPILATION_UNRESOLVED_CONST, 
+        nodeToHighlight, 
+        errorMessage);
+  }
+}

packages/compiler-cli/src/ngtsc/annotations/component/src/resources.ts

@@ -17,7 +17,7 @@ import {DynamicValue, PartialEvaluator, traceDynamicValue} from '../../../partia
 import {ClassDeclaration, DeclarationNode, Decorator} from '../../../reflection';
 import {CompilationMode} from '../../../transform';
 import {TemplateSourceMapping} from '../../../typecheck/api';
-import {createValueHasWrongTypeError, isStringArray, ResourceLoader} from '../../common';
+import {createValueHasWrongTypeError, isStringArray, ResourceLoader, assertLocalCompilationUnresolvedConst} from '../../common';
 
 /**
  * The literal style url extracted from the decorator, along with metadata for diagnostics.
@@ -151,14 +151,13 @@ export function extractTemplate(
       const resolvedTemplate = evaluator.evaluate(template.expression);
 
       // The identifier used for @Component.template cannot be resolved in local compilation mode. An error specific to this situation is generated.
-      if (compilationMode === CompilationMode.LOCAL && resolvedTemplate instanceof DynamicValue &&
-          resolvedTemplate.isFromUnknownIdentifier()) {
-
-        throw new FatalDiagnosticError(
-            ErrorCode.LOCAL_COMPILATION_UNRESOLVED_CONST, 
-            template.expression, 
-            'Unresolved identifier found for @Component.template field! Did you import this identifier from a file outside of the compilation unit? This is not allowed when Angular compiler runs in local mode. Possible solutions: 1) Move the declaration into a file within the compilation unit, 2) Inline the template, 3) Move the template into a separate .html file and include it using @Component.templateUrl');
-      }
+      assertLocalCompilationUnresolvedConst(
+        compilationMode, resolvedTemplate, template.expression, 
+        'Unresolved identifier found for @Component.template field! ' + 
+        'Did you import this identifier from a file outside of the compilation unit? ' + 'This is not allowed when Angular compiler runs in local mode. ' +
+        'Possible solutions: 1) Move the declaration into a file within the ' +
+        'compilation unit, 2) Inline the template, 3) Move the template into ' +
+        'a separate .html file and include it using @Component.templateUrl');
 
       if (typeof resolvedTemplate !== 'string') {
         throw createValueHasWrongTypeError(