Adds tests

Author: arcanis

doc/api/packages.md

@@ -1020,15 +1020,15 @@ When a bare specifier is encountered:
 
 1. Node.js determines which package contains the importing file by checking
    if the file path is within any package's `path`.
-2. If the importing file is not within any mapped package, standard
-   `node_modules` resolution is used.
+2. If the importing file is not within any mapped package, a
+   `MODULE_NOT_FOUND` error is thrown.
 3. Node.js searches the importing package's `dependencies` array for an entry
    whose `name` matches the specifier's package name.
 4. If found, the specifier resolves to that dependency's `path`.
 5. If the package exists in the map but is not in `dependencies`, an
    [`ERR_PACKAGE_MAP_ACCESS_DENIED`][] error is thrown.
-6. If the package does not exist in the map at all, standard `node_modules`
-   resolution is used as a fallback.
+6. If the package does not exist in the map at all, a
+   `MODULE_NOT_FOUND` error is thrown.
 
 ### Subpath resolution
 
@@ -1094,16 +1094,15 @@ const utils = require('@myorg/utils');
 import utils from '@myorg/utils';
 ```
 
-### Fallback behavior
+### Interaction with other resolution
 
-Package maps do not replace `node_modules` resolution entirely. Resolution
-falls back to standard behavior when:
+Package maps only apply to bare specifiers that are not Node.js builtin
+modules. The following cases are not affected by package maps and continue
+to use standard resolution:
 
-* The importing file is not within any package defined in the map.
-* The specifier's package name is not found in any package's `name` field.
-* The specifier is a relative path (`./` or `../`).
-* The specifier is an absolute path or URL.
-* The specifier refers to a Node.js builtin module (`node:fs`, etc.).
+* Relative paths (`./` or `../`).
+* Absolute paths or URLs.
+* Node.js builtin modules (`node:fs`, etc.).
 
 ### Limitations
 

lib/internal/modules/cjs/loader.js

@@ -665,8 +665,15 @@ function tryPackageMapResolveCJS(request, parent, conditions) {
   const parentPath = parent?.filename ?? process.cwd() + path.sep;
   const mapped = packageMapResolve(request, parentPath);
 
-  // Not in package map - fall back to standard resolution
-  if (mapped === undefined) { return undefined; }
+  if (mapped === undefined) {
+    const requireStack = getRequireStack(parent);
+    const message = getRequireStackMessage(request, requireStack);
+    // eslint-disable-next-line no-restricted-syntax
+    const err = new Error(message);
+    err.code = 'MODULE_NOT_FOUND';
+    err.requireStack = requireStack;
+    throw err;
+  }
 
   const { packagePath, subpath } = mapped;
 

lib/internal/modules/package_map.js

@@ -7,12 +7,11 @@ const {
   SafeSet,
   StringPrototypeIndexOf,
   StringPrototypeSlice,
-  StringPrototypeStartsWith,
 } = primordials;
 
 const assert = require('internal/assert');
 const { getLazy } = require('internal/util');
-const { resolve: pathResolve, dirname, sep } = require('path');
+const { resolve: pathResolve, dirname } = require('path');
 
 const getPackageMapPath = getLazy(() =>
   require('internal/options').getOptionValue('--experimental-package-map'),
@@ -117,7 +116,7 @@ class PackageMap {
 
     // Walk up to find containing package
     let checkPath = filePath;
-    while (isPathContainedIn(checkPath, this.#basePath)) {
+    while (true) {
       const keys = this.#pathToKeys.get(checkPath);
       if (keys && keys.size > 0) {
         const key = keys.values().next().value;
@@ -144,7 +143,7 @@ class PackageMap {
   resolve(specifier, parentPath) {
     const parentKey = this.#getKeyForPath(parentPath);
 
-    // Parent not in map - fall back to standard resolution
+    // Parent not in map - let the caller throw the appropriate error
     if (parentKey === null) { return undefined; }
 
     // Check cache
@@ -189,7 +188,7 @@ class PackageMap {
           this.#configPath,
         );
       }
-      // Package not in map at all - fall back to standard resolution
+      // Package not in map at all - let the caller throw the appropriate error
       return undefined;
     }
 
@@ -198,17 +197,6 @@ class PackageMap {
   }
 }
 
-/**
- * Check if a file path is contained within a folder path.
- * Handles edge cases like /foo/bar not matching /foo/barbaz.
- * @param {string} file - The file path to check
- * @param {string} folder - The folder path to check against
- * @returns {boolean}
- */
-function isPathContainedIn(file, folder) {
-  return file === folder || StringPrototypeStartsWith(file, folder + sep);
-}
-
 /**
  * Parse a package specifier into name and subpath.
  * @param {string} specifier

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

@@ -84,7 +84,7 @@ describe('ESM: --experimental-package-map', () => {
 
   // =========== Fallback Behavior ===========
 
-  describe('fallback to standard resolution', () => {
+  describe('resolution boundaries', () => {
     it('falls back for builtin modules', async () => {
       const { code, stdout, stderr } = await spawnPromisified(execPath, [
         '--experimental-package-map', packageMapPath,
@@ -97,17 +97,16 @@ describe('ESM: --experimental-package-map', () => {
       assert.match(stdout, /function/);
     });
 
-    it('falls back when parent not in map', async () => {
+    it('throws when parent not in map', async () => {
       const { code, stderr } = await spawnPromisified(execPath, [
         '--experimental-package-map', packageMapPath,
         '--input-type=module',
         '--eval',
         `import dep from 'dep-a'; console.log(dep);`,
       ], { cwd: '/tmp' });  // Not in any mapped package
 
-      // Should fall back to standard resolution (which will fail)
       assert.notStrictEqual(code, 0);
-      assert.match(stderr, /Cannot find package/);
+      assert.match(stderr, /ERR_MODULE_NOT_FOUND/);
     });
   });
 
@@ -244,4 +243,56 @@ describe('ESM: --experimental-package-map', () => {
       assert.match(stdout, /pkg-value/);
     });
   });
+
+  // =========== External Package Paths ===========
+
+  describe('external package paths', () => {
+    it('resolves packages outside the package map directory via relative paths', async () => {
+      const { code, stdout, stderr } = await spawnPromisified(execPath, [
+        '--experimental-package-map',
+        fixtures.path('package-map/nested-project/package-map-external-deps.json'),
+        '--input-type=module',
+        '--eval',
+        `import dep from 'dep-a'; console.log(dep);`,
+      ], { cwd: fixtures.path('package-map/nested-project/src') });
+
+      assert.strictEqual(code, 0, stderr);
+      assert.match(stdout, /dep-a-value/);
+    });
+  });
+
+  // =========== Longest Path Wins ===========
+
+  describe('longest path wins', () => {
+    const longestPathMap = fixtures.path('package-map/package-map-longest-path.json');
+
+    it('resolves nested package using its own dependencies, not the parent', async () => {
+      // Inner lives at ./root/node_modules/inner which is inside root's
+      // path (./root). The longest matching path should win, so code in
+      // inner should resolve dep-a (inner's dep), not be treated as root.
+      const { code, stdout, stderr } = await spawnPromisified(execPath, [
+        '--experimental-package-map', longestPathMap,
+        '--input-type=module',
+        '--eval',
+        `import inner from 'inner'; console.log(inner);`,
+      ], { cwd: fixtures.path('package-map/root') });
+
+      assert.strictEqual(code, 0, stderr);
+      assert.match(stdout, /inner using dep-a-value/);
+    });
+
+    it('denies access to nested package deps from parent package', async () => {
+      // Root does not list dep-a in its dependencies, so importing it
+      // from root should fail even though inner (nested inside root) can.
+      const { code, stderr } = await spawnPromisified(execPath, [
+        '--experimental-package-map', longestPathMap,
+        '--input-type=module',
+        '--eval',
+        `import dep from 'dep-a';`,
+      ], { cwd: fixtures.path('package-map/root') });
+
+      assert.notStrictEqual(code, 0);
+      assert.match(stderr, /ERR_PACKAGE_MAP_ACCESS_DENIED/);
+    });
+  });
 });

test/fixtures/package-map/nested-project/package-map-external-deps.json

@@ -0,0 +1,14 @@
+{
+  "packages": {
+    "app": {
+      "name": "app",
+      "path": "./src",
+      "dependencies": ["dep-a"]
+    },
+    "dep-a": {
+      "name": "dep-a",
+      "path": "../dep-a",
+      "dependencies": []
+    }
+  }
+}

test/fixtures/package-map/package-map-longest-path.json

@@ -0,0 +1,19 @@
+{
+  "packages": {
+    "root": {
+      "name": "root",
+      "path": "./root",
+      "dependencies": ["inner"]
+    },
+    "inner": {
+      "name": "inner",
+      "path": "./root/node_modules/inner",
+      "dependencies": ["dep-a"]
+    },
+    "dep-a": {
+      "name": "dep-a",
+      "path": "./dep-a",
+      "dependencies": []
+    }
+  }
+}

test/fixtures/package-map/root/node_modules/inner/index.cjs

@@ -70,7 +70,7 @@ describe('CJS: --experimental-package-map', () => {
     });
   });
 
-  describe('fallback behavior', () => {
+  describe('resolution boundaries', () => {
     it('falls back for builtin modules', () => {
       const { status, stdout, stderr } = spawnSync(process.execPath, [
         '--experimental-package-map', packageMapPath,
@@ -85,7 +85,7 @@ describe('CJS: --experimental-package-map', () => {
       assert.match(stdout, /function/);
     });
 
-    it('falls back when parent not in map', () => {
+    it('throws when parent not in map', () => {
       const { status, stderr } = spawnSync(process.execPath, [
         '--experimental-package-map', packageMapPath,
         '-e',
@@ -95,7 +95,6 @@ describe('CJS: --experimental-package-map', () => {
         encoding: 'utf8',
       });
 
-      // Should fall back to standard resolution (which will fail)
       assert.notStrictEqual(status, 0);
       assert.match(stderr, /Cannot find module/);
     });
@@ -182,4 +181,58 @@ describe('CJS: --experimental-package-map', () => {
       assert.match(stdout, /pkg-value/);
     });
   });
+
+  describe('external package paths', () => {
+    it('resolves packages outside the package map directory via relative paths', () => {
+      const { status, stdout, stderr } = spawnSync(process.execPath, [
+        '--experimental-package-map',
+        fixtures.path('package-map/nested-project/package-map-external-deps.json'),
+        '-e',
+        `const dep = require('dep-a'); console.log(dep.default);`,
+      ], {
+        cwd: fixtures.path('package-map/nested-project/src'),
+        encoding: 'utf8',
+      });
+
+      assert.strictEqual(status, 0, stderr);
+      assert.match(stdout, /dep-a-value/);
+    });
+  });
+
+  describe('longest path wins', () => {
+    const longestPathMap = fixtures.path('package-map/package-map-longest-path.json');
+
+    it('resolves nested package using its own dependencies, not the parent', () => {
+      // Inner lives at ./root/node_modules/inner which is inside root's
+      // path (./root). The longest matching path should win, so code in
+      // inner should resolve dep-a (inner's dep), not be treated as root.
+      const { status, stdout, stderr } = spawnSync(process.execPath, [
+        '--experimental-package-map', longestPathMap,
+        '-e',
+        `const inner = require('inner'); console.log(inner.default);`,
+      ], {
+        cwd: fixtures.path('package-map/root'),
+        encoding: 'utf8',
+      });
+
+      assert.strictEqual(status, 0, stderr);
+      assert.match(stdout, /inner using dep-a-value/);
+    });
+
+    it('denies access to nested package deps from parent package', () => {
+      // Root does not list dep-a in its dependencies, so requiring it
+      // from root should fail even though inner (nested inside root) can.
+      const { status, stderr } = spawnSync(process.execPath, [
+        '--experimental-package-map', longestPathMap,
+        '-e',
+        `require('dep-a');`,
+      ], {
+        cwd: fixtures.path('package-map/root'),
+        encoding: 'utf8',
+      });
+
+      assert.notStrictEqual(status, 0);
+      assert.match(stderr, /ERR_PACKAGE_MAP_ACCESS_DENIED/);
+    });
+  });
 });