feat(cjs-to-esm): context-local variables → import.meta.*

recipes/cjs-to-esm/package.json

@@ -4,7 +4,7 @@
   "description": "Codemod to assist CommonJS -> ESM migrations (imports, exports, package.json guidance)",
   "type": "module",
   "scripts": {
-    "test": "echo  \"The test will be runned when implementation is done.\"",
+    "test": "node --run test:context-local-variable",
     "test:import": "npx codemod jssg test -l typescript ./src/import-process.ts ./tests/import",
     "test:export": "npx codemod jssg test -l typescript ./src/export-process.ts ./tests/export",
     "test:package-json": "npx codemod jssg test -l json ./src/package-json-process.ts ./tests/package-json",

recipes/cjs-to-esm/src/context-local-variable-process.ts

@@ -1,14 +1,131 @@
-import type { SgRoot, Edit } from '@codemod.com/jssg-types/main';
+import type { SgRoot, Edit, SgNode } from '@codemod.com/jssg-types/main';
 import type JS from '@codemod.com/jssg-types/langs/javascript';
 
+/**
+ * Returns true when `__dirname` or `__filename` resolves to a local definition
+ * in the current file and should not be transformed.
+ *
+ * @example
+ * // true for: const __dirname = '/tmp';
+ * isShadowedContextLocal(identifier, root)
+ *
+ * @example
+ * // true for: function fn(__filename) { return __filename; }
+ * isShadowedContextLocal(identifier, root)
+ *
+ * @example
+ * // false when using Node.js global `__dirname` with no local binding
+ * isShadowedContextLocal(identifier, root)
+ */
+const isShadowedContextLocal = (
+	node: SgNode<JS>,
+	root: SgRoot<JS>,
+): boolean => {
+	const definition = node.definition();
+
+	if (!definition || definition.kind !== 'local') return false;
+
+	return definition.root.filename() === root.filename();
+};
+
 /**
  * @see https://github.com/nodejs/package-examples/blob/main/guide/05-cjs-esm-migration/migrating-context-local-variables/README.md
  */
 export default function transform(root: SgRoot<JS>): string | null {
 	const rootNode = root.root();
 	const edits: Edit[] = [];
 
-	// do some stuff
+	const requireMainNodes = rootNode.findAll({
+		rule: {
+			kind: 'member_expression',
+			has: {
+				field: 'object',
+				kind: 'identifier',
+				regex: '^require$',
+			},
+			all: [
+				{
+					has: {
+						field: 'property',
+						kind: 'property_identifier',
+						regex: '^main$',
+					},
+				},
+			],
+		},
+	});
+
+	for (const node of requireMainNodes) {
+		const result = node.find({
+			rule: {
+				inside: {
+					kind: 'binary_expression',
+					has: {
+						kind: 'identifier',
+						regex: 'module',
+					},
+				},
+			},
+		});
+
+		if (result) {
+			edits.push(result.replace('import.meta.main'));
+		} else {
+			edits.push(node.replace('import.meta.main'));
+		}
+	}
+
+	const requireResolveNodes = rootNode.findAll({
+		rule: {
+			kind: 'call_expression',
+			has: {
+				field: 'function',
+				kind: 'member_expression',
+				all: [
+					{
+						has: {
+							field: 'object',
+							kind: 'identifier',
+							regex: '^require$',
+						},
+					},
+					{
+						has: {
+							field: 'property',
+							kind: 'property_identifier',
+							regex: '^resolve$',
+						},
+					},
+				],
+			},
+		},
+	});
+
+	for (const node of requireResolveNodes) {
+		const args = node.field('arguments');
+		if (args) edits.push(node.replace(`import.meta.resolve${args.text()}`));
+	}
+
+	const contextLocalIdentifiers = rootNode.findAll({
+		rule: {
+			kind: 'identifier',
+			regex: '^(__filename|__dirname)$',
+		},
+	});
+
+	for (const identifier of contextLocalIdentifiers) {
+		if (isShadowedContextLocal(identifier, root)) continue;
+		const name = identifier.text();
+
+		switch (name) {
+			case '__dirname':
+				edits.push(identifier.replace('import.meta.dirname'));
+				break;
+			case '__filename':
+				edits.push(identifier.replace('import.meta.filename'));
+				break;
+		}
+	}
 
 	if (!edits.length) return null;
 

recipes/cjs-to-esm/tests/context-local-variable/all-shadowed-locals/expected.js

@@ -0,0 +1,8 @@
+const __filename = '/tmp/file.js';
+const __dirname = '/tmp';
+
+function print(__filename, __dirname) {
+    return `${__filename}::${__dirname}`;
+}
+
+console.log(__filename, __dirname, print('a', 'b'));

recipes/cjs-to-esm/tests/context-local-variable/all-shadowed-locals/input.js

@@ -0,0 +1,8 @@
+const __filename = '/tmp/file.js';
+const __dirname = '/tmp';
+
+function print(__filename, __dirname) {
+    return `${__filename}::${__dirname}`;
+}
+
+console.log(__filename, __dirname, print('a', 'b'));

recipes/cjs-to-esm/tests/context-local-variable/already-esm/expected.js

@@ -0,0 +1,8 @@
+const info = {
+    filename: import.meta.filename,
+    dirname: import.meta.dirname,
+    isMain: import.meta.main,
+    resolved: import.meta.resolve('./foo.js'),
+};
+
+console.log(info);

recipes/cjs-to-esm/tests/context-local-variable/already-esm/input.js

@@ -0,0 +1,8 @@
+const info = {
+    filename: import.meta.filename,
+    dirname: import.meta.dirname,
+    isMain: import.meta.main,
+    resolved: import.meta.resolve('./foo.js'),
+};
+
+console.log(info);

recipes/cjs-to-esm/tests/context-local-variable/basic/expected.js

@@ -0,0 +1,8 @@
+const info = {
+    filename: import.meta.filename,
+    dirname: import.meta.dirname,
+    isMain: import.meta.main,
+    resolved: import.meta.resolve('./foo.js'),
+};
+
+console.log(info, import.meta.main);

recipes/cjs-to-esm/tests/context-local-variable/basic/input.js

@@ -0,0 +1,8 @@
+const info = {
+    filename: __filename,
+    dirname: __dirname,
+    isMain: require.main === module,
+    resolved: require.resolve('./foo.js'),
+};
+
+console.log(info, require.main);

recipes/cjs-to-esm/tests/context-local-variable/mixed-transformations/expected.js

@@ -0,0 +1,8 @@
+if (import.meta.main) {
+    boot();
+}
+
+const resolved = import.meta.resolve('./foo.js', { paths: [__dirname] });
+const filePath = `${import.meta.filename}`;
+
+console.log(import.meta.main, resolved, filePath);

recipes/cjs-to-esm/tests/context-local-variable/mixed-transformations/input.js

@@ -0,0 +1,8 @@
+if (require.main === module) {
+    boot();
+}
+
+const resolved = require.resolve('./foo.js', { paths: [__dirname] });
+const filePath = `${__filename}`;
+
+console.log(require.main, resolved, filePath);

recipes/cjs-to-esm/tests/context-local-variable/module-exports-read/expected.js

@@ -0,0 +1,2 @@
+const currentModule = module;
+console.log(exports.value, currentModule.id);

recipes/cjs-to-esm/tests/context-local-variable/module-exports-read/input.js

@@ -0,0 +1,2 @@
+const currentModule = module;
+console.log(exports.value, currentModule.id);

recipes/cjs-to-esm/tests/context-local-variable/require-main-non-comparison/expected.js

@@ -0,0 +1,5 @@
+const shouldRun = Boolean(import.meta.main);
+
+if (shouldRun) {
+    run();
+}

recipes/cjs-to-esm/tests/context-local-variable/require-main-non-comparison/input.js

@@ -0,0 +1,5 @@
+const shouldRun = Boolean(require.main);
+
+if (shouldRun) {
+    run();
+}

recipes/cjs-to-esm/tests/context-local-variable/reverse-comparison/expected.js

@@ -0,0 +1,3 @@
+if (import.meta.main) {
+    start();
+}

recipes/cjs-to-esm/tests/context-local-variable/reverse-comparison/input.js

@@ -0,0 +1,3 @@
+if (module === require.main) {
+    start();
+}

recipes/cjs-to-esm/tests/context-local-variable/shadowed/expected.js

@@ -0,0 +1,12 @@
+console.log(import.meta.dirname);
+
+function read(__filename) {
+    return __filename;
+}
+
+{
+    const __dirname = 'tmp';
+    console.log(__dirname);
+}
+
+console.log(import.meta.filename);

recipes/cjs-to-esm/tests/context-local-variable/shadowed/input.js

@@ -0,0 +1,12 @@
+console.log(__dirname);
+
+function read(__filename) {
+    return __filename;
+}
+
+{
+    const __dirname = 'tmp';
+    console.log(__dirname);
+}
+
+console.log(__filename);