feat: support commonjs-like directory imports (#6)

Author: JakobJingleheimer

README.md

@@ -39,6 +39,7 @@ npx codemod@latest correct-ts-specifiers
 * `.js` → `.d.cts`, `.d.mts`, or `.d.ts`
 * Package.json subimports
 * tsconfig paths (requires a loader)
+* Commonjs-like directory specifiers
 
 Before:
 
@@ -48,9 +49,10 @@ import { URL } from 'node:url';
 import { bar } from '@dep/bar';
 import { foo } from 'foo';
 
+import { Bird } from './Bird';          // a directory
 import { Cat } from './Cat.ts';
-import { Dog } from '…/Dog/index.mjs'; // tsconfig paths
-import { baseUrl } from '#config.js';  // package.json imports
+import { Dog } from '…/Dog/index.mjs';  // tsconfig paths
+import { baseUrl } from '#config.js';   // package.json imports
 
 export { Zed } from './zed';
 
@@ -60,6 +62,7 @@ export const makeLink = (path: URL) => (new URL(path, baseUrl)).href;
 
 const nil = await import('./nil.js');
 
+const bird = new Bird('Tweety');
 const cat = new Cat('Milo');
 const dog = new Dog('Otis');
 ```
@@ -72,9 +75,10 @@ import { URL } from 'node:url';
 import { bar } from '@dep/bar';
 import { foo } from 'foo';
 
+import { Bird } from './Bird/index.ts';
 import { Cat } from './Cat.ts';
-import { Dog } from '…/Dog/index.mts'; // tsconfig paths
-import { baseUrl } from '#config.js';  // package.json imports
+import { Dog } from '…/Dog/index.mts';  // tsconfig paths
+import { baseUrl } from '#config.js';   // package.json imports
 
 export type { Zed } from './zed.d.ts';
 
@@ -84,16 +88,7 @@ export const makeLink = (path: URL) => (new URL(path, baseUrl)).href;
 
 const nil = await import('./nil.ts');
 
+const bird = new Bird('Tweety');
 const cat = new Cat('Milo');
 const dog = new Dog('Otis');
 ```
-
-## Unsupported cases
-
-* Directory / commonjs-like specifiers¹
-
-```ts
-import foo from '..'; // where '..' → '../index.ts' (or similar)
-```
-
-¹ Support may be added in a future release

src/exts.ts

@@ -1,9 +1,15 @@
+/**
+ * A map of JavaScript file extensions to the corresponding TypeScript file extension.
+ */
 export const jsToTSExts = {
 	'.cjs': '.cts',
 	'.mjs': '.mts',
 	'.js': '.ts',
 	'.jsx': '.tsx',
 } as const;
+/**
+ * File extensions that potentially need to be corrected
+ */
 export const suspectExts = {
 	'': '.js',
 	...jsToTSExts,
@@ -14,9 +20,21 @@ export const jsExts = Object.keys(jsToTSExts) as Array<JSExt>;
 export const tsExts = Object.values(jsToTSExts);
 export type TSExt = typeof tsExts[number];
 
+/**
+ * File extensions for TypeScript type declaration files.
+ */
 export const dExts = [
 	'.d.cts',
 	'.d.ts',
 	'.d.mts',
 ] as const;
 export type DExt = typeof dExts[number];
+
+/**
+ * A master list of file extensions to check.
+ */
+export const extSets = new Set([
+	jsExts,
+	tsExts,
+	dExts,
+]);

src/fexists.test.ts

@@ -1,7 +1,6 @@
 import assert from 'node:assert/strict';
 import {
 	type Mock,
-	after,
 	afterEach,
 	before,
 	describe,
@@ -13,7 +12,8 @@ import { fileURLToPath } from 'node:url';
 
 type FSAccess = typeof import('node:fs/promises').access;
 type FExists = typeof import('./fexists.ts').fexists;
-type MockModuleContext = ReturnType<typeof mock.module>;
+type ResolveSpecifier = typeof import('./resolve-specifier.ts').resolveSpecifier;
+// type MockModuleContext = ReturnType<typeof mock.module>;
 
 const RESOLVED_SPECIFIER_ERR = 'Resolved specifier did not match expected';
 
@@ -22,21 +22,26 @@ describe('fexists', () => {
 	const constants = { F_OK: null };
 
 	let mock__access: Mock<FSAccess>['mock'];
-	let mock__fs: MockModuleContext;
+	let mock__resolveSpecifier: Mock<ResolveSpecifier>['mock'];
 
 	before(() => {
 		const access = mock.fn<FSAccess>();
 		({ mock: mock__access } = access);
-		mock__fs = mock.module('node:fs/promises', {
+		mock.module('node:fs/promises', {
 			namedExports: {
 				access,
 				constants,
 			},
 		});
-	});
 
-	after(() => {
-		mock__fs.restore();
+		const resolveSpecifier = mock.fn<ResolveSpecifier>();
+		({ mock: mock__resolveSpecifier } = resolveSpecifier);
+		mock.module('./resolve-specifier.ts', {
+			namedExports: {
+				resolveSpecifier,
+			},
+		});
+		mock__resolveSpecifier.mockImplementation(function MOCK__resolveSpecifier(pp, specifier) { return specifier });
 	});
 
 	describe('when the file exists', () => {
@@ -52,35 +57,34 @@ describe('fexists', () => {
 			mock__access.resetCalls();
 		});
 
-		after(() => {
-			mock__fs.restore();
-		});
-
 		it('should return `true` for a bare specifier', async () => {
+			const specifier = 'foo';
 			const parentUrl = fileURLToPath(import.meta.resolve('./fixtures/e2e/test.js'));
 
-			assert.equal(await fexists(parentUrl, 'foo'), true);
+			assert.equal(await fexists(parentUrl, specifier), true);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				fileURLToPath(import.meta.resolve('./fixtures/e2e/node_modules/foo/foo.js')),
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
 
 		it('should return `true` for a relative specifier', async () => {
-			assert.equal(await fexists(parentPath, 'exists.js'), true);
+			const specifier = 'exists.js';
+			assert.equal(await fexists(parentPath, specifier), true);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'/tmp/exists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
 
 		it('should return `true` for specifier with a query parameter', async () => {
-			assert.equal(await fexists(parentPath, 'exists.js?v=1'), true);
+			const specifier = 'exists.js?v=1';
+			assert.equal(await fexists(parentPath, specifier), true);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'/tmp/exists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
@@ -119,42 +123,42 @@ describe('fexists', () => {
 			mock__access.resetCalls();
 		});
 
-		after(() => {
-			mock__fs.restore();
-		});
-
 		it('should return `false` for a relative specifier', async () => {
-			assert.equal(await fexists(parentPath, 'noexists.js'), false);
+			const specifier = 'noexists.js';
+			assert.equal(await fexists(parentPath, specifier), false);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'/tmp/noexists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
 
 		it('should return `false` for a relative specifier', async () => {
-			assert.equal(await fexists(parentPath, 'noexists.js?v=1'), false);
+			const specifier = 'noexists.js?v=1';
+			assert.equal(await fexists(parentPath, specifier), false);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'/tmp/noexists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
 
 		it('should return `false` for an absolute specifier', async () => {
-			assert.equal(await fexists(parentPath, '/tmp/foo/noexists.js'), false);
+			const specifier = '/tmp/foo/noexists.js';
+			assert.equal(await fexists(parentPath, specifier), false);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'/tmp/foo/noexists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});
 
 		it('should return `false` for a URL specifier', async () => {
-			assert.equal(await fexists(parentPath, 'file://localhost/foo/noexists.js'), false);
+			const specifier = 'file://localhost/foo/noexists.js';
+			assert.equal(await fexists(parentPath, specifier), false);
 			assert.equal(
 				mock__access.calls[0].arguments[0],
-				'file://localhost/foo/noexists.js',
+				specifier,
 				RESOLVED_SPECIFIER_ERR,
 			);
 		});

src/fexists.ts

@@ -1,22 +1,14 @@
-import { dirname } from 'node:path';
 import { access, constants } from 'node:fs/promises';
-import { fileURLToPath, pathToFileURL } from 'node:url';
 
 import type { FSAbsolutePath, Specifier } from './index.d.ts';
+import { resolveSpecifier } from './resolve-specifier.ts';
 
 
 export function fexists(
 	parentPath: FSAbsolutePath,
 	specifier: Specifier,
 ) {
-	const parentUrl = `${pathToFileURL(dirname(parentPath)).href}/`;
-
-	const resolvedSpecifier: FSAbsolutePath = URL.canParse(specifier)
-    ? specifier
-    // import.meta.resolve gives access to node's resolution algorithm, which is necessary to handle
-		// a myriad of non-obvious routes, like pJson subimports and the result of any hooks that may be
-		// helping, such as ones facilitating tsconfig's "paths"
-		: fileURLToPath(import.meta.resolve(specifier, parentUrl));
+	const resolvedSpecifier = resolveSpecifier(parentPath, specifier);
 
 	return access(
 		resolvedSpecifier,