Adds a test for symlinks in the package map ancestors

Author: arcanis

doc/api/packages.md

@@ -966,8 +966,8 @@ This feature is useful for:
   packages without symlinks or hoisting complexities.
 * **Dependency isolation**: Prevent packages from accessing undeclared
   dependencies (phantom dependencies).
-* **Multiple versions**: Allow different packages to depend on different
-  versions of the same dependency.
+* **Low filesystem coupling**: The package resolution algorithm runs without
+  inspecting the filesystem, relying instead on static data tables.
 
 ### Configuration file format
 

lib/internal/modules/package_map.js

@@ -217,6 +217,10 @@ function loadPackageMap(configPath) {
     throw new ERR_PACKAGE_MAP_INVALID(configPath, err.message);
   }
 
+  // Resolve symlinks so that stored paths match the realpath'd module paths
+  // that Node.js uses during resolution.
+  configPath = fs.realpathSync(configPath);
+
   let data;
   try {
     data = JSONParse(content);

test/es-module/test-esm-package-map.mjs

@@ -1,8 +1,9 @@
-import { spawnPromisified } from '../common/index.mjs';
+import { canCreateSymLink, spawnPromisified } from '../common/index.mjs';
 import * as fixtures from '../common/fixtures.mjs';
 import tmpdir from '../common/tmpdir.js';
 import assert from 'node:assert';
-import { writeFileSync } from 'node:fs';
+import { symlinkSync, writeFileSync } from 'node:fs';
+import path from 'node:path';
 import { execPath } from 'node:process';
 import { describe, it } from 'node:test';
 import { pathToFileURL } from 'node:url';
@@ -375,4 +376,28 @@ describe('ESM: --experimental-package-map', () => {
       assert.notStrictEqual(code, 0, stderr);
     });
   });
+
+  // =========== Symlink in Ancestor ===========
+
+  describe('symlink in ancestor of package map', {
+    skip: !canCreateSymLink() && 'insufficient privileges for symlinks',
+  }, () => {
+    const symlinkDir = tmpdir.resolve('symlinked-package-map-esm');
+    symlinkSync(fixtures.path('package-map'), symlinkDir, 'dir');
+
+    it('resolves through a symlinked ancestor directory', async () => {
+      const symlinkMapPath = path.join(symlinkDir, 'package-map.json');
+      const { code, stdout, stderr } = await spawnPromisified(execPath, [
+        '--no-warnings',
+        '--experimental-package-map', symlinkMapPath,
+        '--input-type=module',
+        '--eval',
+        `import dep from 'dep-a'; console.log(dep);`,
+      ], { cwd: fixtures.path('package-map/root') });
+
+      assert.strictEqual(stderr, '');
+      assert.match(stdout, /dep-a-value/);
+      assert.strictEqual(code, 0, stderr);
+    });
+  });
 });

test/parallel/test-require-package-map.js

@@ -1,10 +1,11 @@
 'use strict';
 
-require('../common');
+const common = require('../common');
 const fixtures = require('../common/fixtures');
 const assert = require('node:assert');
 const { spawnSync } = require('node:child_process');
-const { writeFileSync } = require('node:fs');
+const { symlinkSync, writeFileSync } = require('node:fs');
+const path = require('node:path');
 const { describe, it } = require('node:test');
 const { pathToFileURL } = require('node:url');
 const tmpdir = require('../common/tmpdir');
@@ -335,4 +336,28 @@ describe('CJS: --experimental-package-map', { concurrency: !process.env.TEST_PAR
       assert.notStrictEqual(status, 0);
     });
   });
+
+  describe('symlink in ancestor of package map', {
+    skip: !common.canCreateSymLink() && 'insufficient privileges for symlinks',
+  }, () => {
+    const symlinkDir = tmpdir.resolve('symlinked-package-map-cjs');
+    symlinkSync(fixtures.path('package-map'), symlinkDir, 'dir');
+
+    it('resolves through a symlinked ancestor directory', () => {
+      const symlinkMapPath = path.join(symlinkDir, 'package-map.json');
+      const { status, stdout, stderr } = spawnSync(process.execPath, [
+        '--no-warnings',
+        '--experimental-package-map', symlinkMapPath,
+        '-e',
+        `const dep = require('dep-a'); console.log(dep.default);`,
+      ], {
+        cwd: fixtures.path('package-map/root'),
+        encoding: 'utf8',
+      });
+
+      assert.strictEqual(stderr, '');
+      assert.match(stdout, /dep-a-value/);
+      assert.strictEqual(status, 0, stderr);
+    });
+  });
 });