fix(ngcc): correctly detect imported TypeScript helpers (#36284)

The `NgccReflectionHost`s have logic for detecting certain known
declarations (such as `Object.assign()` and TypeScript helpers), which
allows the `PartialEvaluator` to evaluate expressions it would not be
able to statically evaluate otherwise.

In #36089, `DelegatingReflectionHost` was introduced, which delegates to
a TypeScript `ReflectionHost` when reflecting on TypeScript files, which
for ngcc's case means `.d.ts` files of dependencies. As a result, ngcc
lost the ability to detect TypeScript helpers imported from `tslib`,
because `DelegatingReflectionHost` was not able to apply the known
declaration detection logic while reflecting on `tslib`'s `.d.ts` files.

This commit fixes this by ensuring `DelegatingReflectionHost` calls the
`NgccReflectionHost`'s `detectKnownDeclaration()` method as necessary,
even when using the TypeScript `ReflectionHost`.

NOTE:
The previous commit exposed a bug in ngcc that was hidden due to the
tests' being inconsistent with how the `ReflectionHost`s are used in the
actual program. The changes in this commit are verified by ensuring the
failing tests are now passing (hence no new tests are added).

PR Close #36284

Author: gkalpak

packages/compiler-cli/ngcc/src/host/delegating_host.ts

@@ -32,7 +32,7 @@ export class DelegatingReflectionHost implements NgccReflectionHost {
 
   getDeclarationOfIdentifier(id: ts.Identifier): Declaration|null {
     if (isFromDtsFile(id)) {
-      return this.tsHost.getDeclarationOfIdentifier(id);
+      return this.detectKnownDeclaration(this.tsHost.getDeclarationOfIdentifier(id));
     }
     return this.ngccHost.getDeclarationOfIdentifier(id);
   }
@@ -60,7 +60,13 @@ export class DelegatingReflectionHost implements NgccReflectionHost {
 
   getExportsOfModule(module: ts.Node): Map<string, Declaration>|null {
     if (isFromDtsFile(module)) {
-      return this.tsHost.getExportsOfModule(module);
+      const exportMap = this.tsHost.getExportsOfModule(module);
+
+      if (exportMap !== null) {
+        exportMap.forEach(decl => this.detectKnownDeclaration(decl));
+      }
+
+      return exportMap;
     }
     return this.ngccHost.getExportsOfModule(module);
   }
@@ -154,4 +160,11 @@ export class DelegatingReflectionHost implements NgccReflectionHost {
   getEndOfClass(classSymbol: NgccClassSymbol): ts.Node {
     return this.ngccHost.getEndOfClass(classSymbol);
   }
+
+  detectKnownDeclaration(decl: null): null;
+  detectKnownDeclaration<T extends Declaration>(decl: T): T;
+  detectKnownDeclaration<T extends Declaration>(decl: T|null): T|null;
+  detectKnownDeclaration<T extends Declaration>(decl: T|null): T|null {
+    return this.ngccHost.detectKnownDeclaration(decl);
+  }
 }

packages/compiler-cli/ngcc/src/host/ngcc_host.ts

@@ -7,12 +7,12 @@
  */
 import * as ts from 'typescript';
 
-import {ClassDeclaration, ConcreteDeclaration, Decorator, ReflectionHost} from '../../../src/ngtsc/reflection';
+import {ClassDeclaration, ConcreteDeclaration, Declaration, Decorator, ReflectionHost} from '../../../src/ngtsc/reflection';
 
 export const PRE_R3_MARKER = '__PRE_R3__';
 export const POST_R3_MARKER = '__POST_R3__';
 
-export type SwitchableVariableDeclaration = ts.VariableDeclaration & {initializer: ts.Identifier};
+export type SwitchableVariableDeclaration = ts.VariableDeclaration&{initializer: ts.Identifier};
 export function isSwitchableVariableDeclaration(node: ts.Node):
     node is SwitchableVariableDeclaration {
   return ts.isVariableDeclaration(node) && !!node.initializer &&
@@ -47,7 +47,7 @@ export interface ModuleWithProvidersFunction {
  * The symbol corresponding to a "class" declaration. I.e. a `ts.Symbol` whose `valueDeclaration` is
  * a `ClassDeclaration`.
  */
-export type ClassSymbol = ts.Symbol & {valueDeclaration: ClassDeclaration};
+export type ClassSymbol = ts.Symbol&{valueDeclaration: ClassDeclaration};
 
 /**
  * A representation of a class that accounts for the potential existence of two `ClassSymbol`s for a
@@ -128,4 +128,13 @@ export interface NgccReflectionHost extends ReflectionHost {
    * @param classSymbol The class whose statements we want.
    */
   getEndOfClass(classSymbol: NgccClassSymbol): ts.Node;
+
+  /**
+   * Check whether a `Declaration` corresponds with a known declaration and set its `known` property
+   * to the appropriate `KnownDeclaration`.
+   *
+   * @param decl The `Declaration` to check or `null` if there is no declaration.
+   * @return The passed in `Declaration` (potentially enhanced with a `KnownDeclaration`).
+   */
+  detectKnownDeclaration<T extends Declaration>(decl: T|null): T|null;
 }