feat(compiler-cli): support partial evaluation and ReturnType in isolated declarations

attempt to statically evaluate @NgModule imports and exports in isolated declarations mode.
if resolution succeeds, emit the resolved values as concrete references.
if resolution fails, fall back to purely syntactic transforms, such as transforming calls to ReturnType<typeof ...>.

also add validation to ensure expressions falling back to typeof are valid entity names,
producing a LOCAL_COMPILATION_UNSUPPORTED_EXPRESSION diagnostic otherwise.

this allows emitting correct type references in .d.ts files without needing full resolution of external references, while supporting common patterns like forRoot() and local evaluation where possible.

TAG=agy
CONV=51a2b6d6-5679-49cf-8fa6-61fbc69628be

Author: alxhub

packages/compiler-cli/src/ngtsc/annotations/ng_module/src/handler.ts

@@ -31,6 +31,7 @@ import {
   ReturnStatement,
   SchemaMetadata,
   Statement,
+  TypeofExpr,
   WrappedNodeExpr,
 } from '@angular/compiler';
 import ts from 'typescript';
@@ -45,6 +46,7 @@ import {
   assertSuccessfulReferenceEmit,
   LocalCompilationExtraImportsTracker,
   Reference,
+  ReferenceEmitKind,
   ReferenceEmitter,
 } from '../../../imports';
 import {
@@ -104,6 +106,7 @@ import {
   ReferencesRegistry,
   resolveProvidersRequiringFactory,
   toR3Reference,
+  tryUnwrapForwardRef,
   unwrapExpression,
   wrapFunctionExpressionsInParens,
   wrapTypeReference,
@@ -352,14 +355,21 @@ export class NgModuleDecoratorHandler implements DecoratorHandler<
       return {};
     }
 
+    // In declaration-only emission the `declarations`/`imports`/`exports` arrays are emitted via a
+    // purely syntactic transform - we don't attempt static resolution at all (that machinery is
+    // only needed for the regular emit path) and produce the `Isolated` metadata kind directly
+    // from the raw decorator expressions.
+    if (this.emitDeclarationOnly) {
+      return this.analyzeForDeclarationOnly(node, name, ngModule, decorator);
+    }
+
     const forwardRefResolver = createForwardRefResolver(this.isCore);
     const moduleResolvers = combineResolvers([
       createModuleWithProvidersResolver(this.reflector, this.isCore),
       forwardRefResolver,
     ]);
 
-    const allowUnresolvedReferences =
-      this.compilationMode === CompilationMode.LOCAL && !this.emitDeclarationOnly;
+    const allowUnresolvedReferences = this.compilationMode === CompilationMode.LOCAL;
     const diagnostics: ts.Diagnostic[] = [];
 
     // Resolving declarations
@@ -552,6 +562,7 @@ export class NgModuleDecoratorHandler implements DecoratorHandler<
     const type = wrapTypeReference(node);
 
     let ngModuleMetadata: R3NgModuleMetadata;
+
     if (allowUnresolvedReferences) {
       ngModuleMetadata = {
         kind: R3NgModuleMetadataKind.Local,
@@ -1093,6 +1104,119 @@ export class NgModuleDecoratorHandler implements DecoratorHandler<
     }
   }
 
+  /**
+   * Analyze path used in `emitDeclarationOnly` (isolated declarations) mode. The
+   * `declarations`/`imports`/`exports` arrays are NOT statically resolved here - they're transformed
+   * syntactically into the `Isolated` metadata kind's type-tuple expressions, which downstream
+   * `.d.ts` metadata readers resolve. This skips the partial-evaluator path entirely.
+   */
+  private analyzeForDeclarationOnly(
+    node: ClassDeclaration,
+    name: string,
+    ngModule: Map<string, ts.Expression>,
+    decorator: Readonly<Decorator>,
+  ): AnalysisOutput<NgModuleAnalysis> {
+    const diagnostics: ts.Diagnostic[] = [];
+    const rawDeclarations = ngModule.get('declarations') ?? null;
+    const rawImports = ngModule.get('imports') ?? null;
+    const rawExports = ngModule.get('exports') ?? null;
+    const rawBootstrap = ngModule.get('bootstrap') ?? null;
+    const rawProviders = ngModule.has('providers') ? ngModule.get('providers')! : null;
+
+    let id: Expression | null = null;
+    if (ngModule.has('id')) {
+      const idExpr = ngModule.get('id')!;
+      if (!isModuleIdExpression(idExpr)) {
+        id = new WrappedNodeExpr(idExpr);
+      }
+    }
+
+    const type = wrapTypeReference(node);
+
+    const ngModuleMetadata: R3NgModuleMetadata = {
+      kind: R3NgModuleMetadataKind.Isolated,
+      type,
+      bootstrapExpression: rawBootstrap ? new WrappedNodeExpr(rawBootstrap) : null,
+      declarationsExpression: null,
+      importsExpression: rawImports
+        ? transformToTypeTupleExpression(
+            rawImports,
+            this.evaluator,
+            this.refEmitter,
+            node.getSourceFile(),
+            this.reflector,
+            diagnostics,
+          )
+        : null,
+      exportsExpression: rawExports
+        ? transformToTypeTupleExpression(
+            rawExports,
+            this.evaluator,
+            this.refEmitter,
+            node.getSourceFile(),
+            this.reflector,
+            diagnostics,
+          )
+        : null,
+      id,
+      selectorScopeMode: R3SelectorScopeMode.Omit,
+      schemas: [],
+    };
+
+    // Providers are emitted as-is - they are needed for the injector but don't go through any
+    // resolution at this stage.
+    let wrappedProviders: WrappedNodeExpr<ts.Expression> | null = null;
+    if (
+      rawProviders !== null &&
+      (!ts.isArrayLiteralExpression(rawProviders) || rawProviders.elements.length > 0)
+    ) {
+      wrappedProviders = new WrappedNodeExpr(
+        this.annotateForClosureCompiler
+          ? wrapFunctionExpressionsInParens(rawProviders)
+          : rawProviders,
+      );
+    }
+
+    const injectorMetadata: R3InjectorMetadata = {
+      name,
+      type,
+      providers: wrappedProviders,
+      imports: [],
+    };
+
+    const factoryMetadata: R3FactoryMetadata = {
+      name,
+      type,
+      typeArgumentCount: 0,
+      deps: getValidConstructorDependencies(node, this.reflector, this.isCore),
+      target: FactoryTarget.NgModule,
+    };
+
+    return {
+      diagnostics: diagnostics.length > 0 ? diagnostics : undefined,
+      analysis: {
+        id,
+        schemas: [],
+        mod: ngModuleMetadata,
+        inj: injectorMetadata,
+        fac: factoryMetadata,
+        declarations: [],
+        rawDeclarations,
+        imports: [],
+        rawImports,
+        importRefs: [],
+        exports: [],
+        rawExports,
+        providers: rawProviders,
+        providersRequiringFactory: null,
+        classMetadata: null,
+        factorySymbolName: node.name.text,
+        remoteScopesMayRequireCycleProtection: false,
+        decorator: (decorator?.node as ts.Decorator | null) ?? null,
+      },
+    };
+  }
+
   // Verify that a "Declaration" reference is a `ClassDeclaration` reference.
   private isClassDeclarationReference(ref: Reference): ref is Reference<ClassDeclaration> {
     return this.reflector.isClass(ref.node);
@@ -1176,17 +1300,6 @@ export class NgModuleDecoratorHandler implements DecoratorHandler<
       } else if (entry instanceof DynamicValue && allowUnresolvedReferences) {
         dynamicValueSet.add(entry);
         continue;
-      } else if (
-        this.emitDeclarationOnly &&
-        entry instanceof DynamicValue &&
-        entry.isFromUnknownIdentifier()
-      ) {
-        throw createValueHasWrongTypeError(
-          entry.node,
-          entry,
-          `Value at position ${absoluteIndex} in the NgModule.${arrayName} of ${className} is an external reference. ` +
-            'External references in @NgModule declarations are not supported in experimental declaration-only emission mode',
-        );
       } else {
         // TODO(alxhub): Produce a better diagnostic here - the array index may be an inner array.
         throw createValueHasWrongTypeError(
@@ -1257,3 +1370,129 @@ function makeStandaloneBootstrapDiagnostic(
 function isSyntheticReference(ref: Reference<DeclarationNode>): boolean {
   return ref.synthetic;
 }
+
+/**
+ * Converts a value expression that is an identifier or a chain of property accesses on identifiers
+ * (e.g. `Foo` or `Foo.bar`) into the equivalent `ts.EntityName`, reusing the original identifier
+ * nodes so that any imports they reference are preserved by TypeScript's declaration emitter.
+ * Returns `null` for any other shape of expression.
+ */
+function expressionToEntityName(expr: ts.Expression): ts.EntityName | null {
+  if (ts.isIdentifier(expr)) {
+    return expr;
+  }
+  if (ts.isPropertyAccessExpression(expr) && ts.isIdentifier(expr.name)) {
+    const left = expressionToEntityName(expr.expression);
+    return left === null ? null : ts.factory.createQualifiedName(left, expr.name.text);
+  }
+  return null;
+}
+
+function transformToTypeTupleElement(
+  el: ts.Expression,
+  reflector: ReflectionHost,
+  diagnostics: ts.Diagnostic[],
+): Expression {
+  el = unwrapExpression(el);
+
+  const forwardRefUnwrapped = tryUnwrapForwardRef(el, reflector);
+  if (forwardRefUnwrapped !== null) {
+    return transformToTypeTupleElement(forwardRefUnwrapped, reflector, diagnostics);
+  }
+
+  // A call expression (e.g. `Foo.forRoot()` or a bare `fn()`) cannot be referenced with a
+  // `typeof` query directly. Instead emit `ReturnType<typeof callee>` so that the `.d.ts`
+  // reader can resolve the (potentially `ModuleWithProviders<T>`) return type later.
+  if (ts.isCallExpression(el)) {
+    const callee = expressionToEntityName(el.expression);
+    if (callee !== null) {
+      return new WrappedNodeExpr(
+        ts.factory.createTypeReferenceNode(ts.factory.createIdentifier('ReturnType'), [
+          ts.factory.createTypeQueryNode(callee),
+        ]),
+      );
+    }
+  }
+
+  if (expressionToEntityName(el) === null) {
+    const diag = makeDiagnostic(
+      ErrorCode.LOCAL_COMPILATION_UNSUPPORTED_EXPRESSION,
+      el,
+      `In experimental declaration-only emission mode, this expression is not supported in NgModule imports/exports as it cannot be referenced with 'typeof'. Use a direct reference or a supported call.`,
+    );
+    diagnostics.push(diag);
+    return new WrappedNodeExpr(ts.factory.createKeywordTypeNode(ts.SyntaxKind.NeverKeyword));
+  }
+
+  return new TypeofExpr(new WrappedNodeExpr(el));
+}
+
+function resolvedToTypeTupleElement(
+  originalEl: ts.Expression,
+  resolved: ResolvedValue,
+  refEmitter: ReferenceEmitter,
+  sourceFile: ts.SourceFile,
+  reflector: ReflectionHost,
+  diagnostics: ts.Diagnostic[],
+): Expression {
+  if (resolved instanceof Reference) {
+    const emitted = refEmitter.emit(resolved, sourceFile);
+    if (emitted.kind === ReferenceEmitKind.Success) {
+      return new TypeofExpr(emitted.expression);
+    }
+  }
+
+  if (Array.isArray(resolved)) {
+    const elements: Expression[] = [];
+    let allValid = true;
+    for (const item of resolved) {
+      if (item instanceof Reference) {
+        const emitted = refEmitter.emit(item, sourceFile);
+        if (emitted.kind === ReferenceEmitKind.Success) {
+          elements.push(new TypeofExpr(emitted.expression));
+          continue;
+        }
+      }
+      allValid = false;
+      break;
+    }
+    if (allValid && elements.length > 0) {
+      return new LiteralArrayExpr(elements);
+    }
+  }
+
+  // Fallback to syntactic transform
+  return transformToTypeTupleElement(originalEl, reflector, diagnostics);
+}
+
+function transformToTypeTupleExpression(
+  expr: ts.Expression,
+  evaluator: PartialEvaluator,
+  refEmitter: ReferenceEmitter,
+  sourceFile: ts.SourceFile,
+  reflector: ReflectionHost,
+  diagnostics: ts.Diagnostic[],
+): Expression | null {
+  if (ts.isArrayLiteralExpression(expr)) {
+    // An empty array is treated like an omitted slot (emitted as `never` by
+    // `createNgModuleType`), matching the standard compilation path.
+    if (expr.elements.length === 0) {
+      return null;
+    }
+    return new LiteralArrayExpr(
+      expr.elements.map((el) => {
+        const resolved = evaluator.evaluate(el);
+        return resolvedToTypeTupleElement(
+          el,
+          resolved,
+          refEmitter,
+          sourceFile,
+          reflector,
+          diagnostics,
+        );
+      }),
+    );
+  }
+  const resolved = evaluator.evaluate(expr);
+  return resolvedToTypeTupleElement(expr, resolved, refEmitter, sourceFile, reflector, diagnostics);
+}

packages/compiler-cli/src/ngtsc/metadata/BUILD.bazel

@@ -12,6 +12,7 @@ ts_project(
         "//packages/compiler",
         "//packages/compiler-cli/src/ngtsc/file_system",
         "//packages/compiler-cli/src/ngtsc/imports",
+        "//packages/compiler-cli/src/ngtsc/partial_evaluator",
         "//packages/compiler-cli/src/ngtsc/reflection",
         "//packages/compiler-cli/src/ngtsc/util",
     ],