Implement package exports and subpath imports handling

src/converter/convertFile.test.ts

@@ -50,6 +50,10 @@ describe('convertFile', () => {
     it('handles named imports from require statements', async () => {
       await testFileConversion('cjs-destructuring');
     });
+
+    it('handles package exports (legacy vs modern packages)', async () => {
+      await testFileConversion('package-exports');
+    });
   });
 
   describe('exports', () => {

src/test/fixtures/package-exports/src/main.snap.ts

@@ -0,0 +1,9 @@
+import omit from 'lodash/omit.js';
+import {HttpsError} from 'firebase-functions/v1/https';
+
+const object = {a: 1, b: '2', c: 3};
+omit(object, ['a', 'c']);
+
+export function logError() {
+  console.log(HttpsError);
+}

src/test/fixtures/package-exports/src/main.ts

@@ -0,0 +1,9 @@
+import omit from 'lodash/omit';
+import {HttpsError} from 'firebase-functions/v1/https';
+
+const object = {a: 1, b: '2', c: 3};
+omit(object, ['a', 'c']);
+
+export function logError() {
+  console.log(HttpsError);
+}

src/test/fixtures/package-exports/tsconfig.json

@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "ESNext",
+    "moduleResolution": "node",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true
+  },
+  "include": ["src/**/*"]
+}

src/util/PathUtil.test.ts

@@ -2,6 +2,7 @@ import {
   findBestMatch,
   getNormalizedPath,
   hasRelativePath,
+  hasPackageExports,
   isMatchingPath,
   removePathAlias,
   removeWildCards,
@@ -94,4 +95,20 @@ describe('PathUtil', () => {
       expect(hasRelativePath('vitest')).toBe(false);
     });
   });
+
+  describe('hasPackageExports', () => {
+    const packageExportsTestDir = '/home/runner/work/ts2esm/ts2esm/src/test/fixtures/package-exports/node_modules';
+
+    it('detects packages with exports field', () => {
+      expect(hasPackageExports(`${packageExportsTestDir}/firebase-functions`)).toBe(true);
+    });
+
+    it('detects packages without exports field', () => {
+      expect(hasPackageExports(`${packageExportsTestDir}/lodash`)).toBe(false);
+    });
+
+    it('returns false for non-existent packages', () => {
+      expect(hasPackageExports('/non/existent/path')).toBe(false);
+    });
+  });
 });

src/util/PathUtil.ts

@@ -62,3 +62,16 @@ export function isNodeModuleRoot(directory: string): boolean {
   const packageJsonExists = fs.existsSync(packageJsonPath);
   return isInNodeModules && packageJsonExists;
 }
+
+export function hasPackageExports(packageDirectory: string): boolean {
+  try {
+    const packageJsonPath = path.join(packageDirectory, 'package.json');
+    if (!fs.existsSync(packageJsonPath)) {
+      return false;
+    }
+    const packageJson = JSON.parse(fs.readFileSync(packageJsonPath, 'utf-8'));
+    return !!packageJson.exports;
+  } catch {
+    return false;
+  }
+}

src/util/replaceModulePath.ts

@@ -2,7 +2,7 @@ import {SourceFile, StringLiteral} from 'ts-morph';
 import {ModuleInfo, parseInfo} from '../parser/InfoParser.js';
 import {ProjectUtil} from './ProjectUtil.js';
 import {toImport, toImportAttribute} from '../converter/ImportConverter.js';
-import {getNormalizedPath, isNodeModuleRoot} from './PathUtil.js';
+import {getNormalizedPath, isNodeModuleRoot, hasPackageExports} from './PathUtil.js';
 import path from 'node:path';
 import {PathFinder} from './PathFinder.js';
 
@@ -27,6 +27,17 @@ export function replaceModulePath({
   return false;
 }
 
+function getPackageNameFromModulePath(modulePath: string): string {
+  // Handle scoped packages like @scope/package-name/subpath
+  if (modulePath.startsWith('@')) {
+    const parts = modulePath.split('/');
+    return parts.length >= 2 ? `${parts[0]}/${parts[1]}` : modulePath;
+  }
+  // Handle regular packages like package-name/subpath
+  const parts = modulePath.split('/');
+  return parts[0] || modulePath;
+}
+
 function createReplacementPath({
   hasAttributesClause,
   info,
@@ -44,6 +55,18 @@ function createReplacementPath({
 
   const comesFromPathAlias = !!info.pathAlias && !!paths;
   const isNodeModulesPath = !info.isRelative && info.normalized.includes('/') && !comesFromPathAlias;
+
+  // For node modules imports, check if the package has exports field
+  if (isNodeModulesPath) {
+    const packageName = getPackageNameFromModulePath(info.normalized);
+    const packageDirectory = path.join(projectDirectory, 'node_modules', packageName);
+
+    // If package has exports field, don't modify the import (modern package)
+    if (hasPackageExports(packageDirectory)) {
+      return null;
+    }
+  }
+
   if (info.isRelative || comesFromPathAlias || isNodeModulesPath) {
     if (['.json', '.css'].includes(info.extension)) {
       return toImportAttribute(info);