fix(compiler-cli): resolve rootDirs to absolute

Ensure that `rootDirs` are absolute by resolving them against the current working directory.

Fixes #36290

packages/compiler-cli/src/ngtsc/util/src/typescript.ts

@@ -10,7 +10,7 @@ const TS = /\.tsx?$/i;
 const D_TS = /\.d\.ts$/i;
 
 import * as ts from 'typescript';
-import {AbsoluteFsPath, absoluteFrom} from '../../file_system';
+import {AbsoluteFsPath, getFileSystem} from '../../file_system';
 import {DeclarationNode} from '../../reflection';
 
 export function isDtsPath(filePath: string): boolean {
@@ -96,19 +96,21 @@ export function getRootDirs(
     host: Pick<ts.CompilerHost, 'getCurrentDirectory'|'getCanonicalFileName'>,
     options: ts.CompilerOptions): AbsoluteFsPath[] {
   const rootDirs: string[] = [];
+  const cwd = host.getCurrentDirectory();
+  const fs = getFileSystem();
   if (options.rootDirs !== undefined) {
     rootDirs.push(...options.rootDirs);
   } else if (options.rootDir !== undefined) {
     rootDirs.push(options.rootDir);
   } else {
-    rootDirs.push(host.getCurrentDirectory());
+    rootDirs.push(cwd);
   }
 
   // In Windows the above might not always return posix separated paths
   // See:
   // https://github.com/Microsoft/TypeScript/blob/3f7357d37f66c842d70d835bc925ec2a873ecfec/src/compiler/sys.ts#L650
   // Also compiler options might be set via an API which doesn't normalize paths
-  return rootDirs.map(rootDir => absoluteFrom(host.getCanonicalFileName(rootDir)));
+  return rootDirs.map(rootDir => fs.resolve(cwd, host.getCanonicalFileName(rootDir)));
 }
 
 export function nodeDebugInfo(node: ts.Node): string {

packages/compiler-cli/src/ngtsc/util/test/typescript_spec.ts

@@ -0,0 +1,30 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {FileSystem, getFileSystem} from '../../file_system';
+import {runInEachFileSystem} from '../../file_system/testing';
+import {getRootDirs} from '../src/typescript';
+
+runInEachFileSystem(() => {
+  let fs: FileSystem;
+
+  beforeEach(() => {
+    fs = getFileSystem();
+  });
+
+  describe('typescript', () => {
+    it('should allow relative root directories', () => {
+      const mockCompilerHost = {
+        getCanonicalFileName: (val: string) => val,
+        getCurrentDirectory: () => '/fs-root/projects'
+      };
+      const result = getRootDirs(mockCompilerHost, {rootDir: './test-project-root'});
+      expect(result).toEqual([fs.resolve('/fs-root/projects/test-project-root')]);
+    });
+  });
+});