Fix ERR_MODULE_NOT_FOUND for TypeScript/ESM imports

[mohammedahmed18]

Problem

Codeflash was generating import statements without file extensions for TypeScript and ESM projects, causing ERR_MODULE_NOT_FOUND errors when Node.js tried to resolve the modules.

Example Error

From trace 08d0e99e-10e6-4ad2-981d-b907e3c068ea:

Error [ERR_MODULE_NOT_FOUND]: Cannot find module
'/workspace/target/packages/microservices/server/server-factory'
imported from .../test_create__unit_test_0.test.ts

The generated test had:

import ServerFactory from '../../server/server-factory'

But Node.js ESM requires explicit file extensions.

Root Cause

The get_module_path method in JavaScriptSupport was unconditionally removing file extensions with .with_suffix(""), regardless of whether the project used ESM or CommonJS module system.

Solution

Modified get_module_path to:

1. Detect the module system using detect_module_system()
2. For ESM or TypeScript files: add .js extension (TypeScript convention)
3. For CommonJS: keep no extension (backward compatible)

TypeScript convention: Use .js extension in imports even when the source file is .ts, as imports reference the compiled output. This is required for Node.js ESM resolution.

Testing

• ✅ Added two new test cases in TestGetModulePath class
• ✅ All 73 existing JavaScript support tests pass
• ✅ All 28 module system tests pass
• ✅ Lint and type checks pass (uv run prek)

Files Changed

• codeflash/languages/javascript/support.py - Fixed get_module_path method
• tests/test_languages/test_javascript_support.py - Added regression tests

Related Issues

Fixes the issue seen in multiple Nest.js optimization runs where generated tests failed with ERR_MODULE_NOT_FOUND.

[claude]

Claude finished @mohammedahmed18's task in 3m 2s —— View job

---

PR Review Summary

• Triage PR size — SMALL (43 lines of production code changed)
• Lint and type checks — prek passes; mypy errors are pre-existing
• Resolve stale review threads — none found
• Code review
• Duplicate detection
• Post summary

---

Prek Checks

All ruff check and ruff format checks pass. Mypy shows 32 pre-existing errors in support.py (e.g., TypeScriptSupport registration error) — none introduced by this PR.

Code Review

Fix is correct for the primary use case. TypeScript files (.ts, .tsx, .mts) are identified by extension in detect_module_system, so they correctly receive the .js suffix regardless of package.json. CommonJS behavior is preserved. The change is backward-compatible.

One potential bug — detect_module_system is called with the original project_root argument, not the resolved project_root_from_lang derived a few lines earlier (support.py:2212):

# project_root_from_lang is computed at line 2195 but NOT used here:
module_system = detect_module_system(project_root, source_file)  # uses original arg

For .js files in an ESM monorepo where package.json lives at project_root_from_lang (not at the passed-in project_root), the ESM detection would fall through to file-content analysis or default to CommonJS, and the .js extension wouldn't be appended. TypeScript files are unaffected (extension-based detection). Fix this →

Minor: ModuleSystem is an informal string-constant class rather than enum.Enum. Not introduced by this PR, so not blocking.

Duplicate Detection

No duplicates detected. get_module_path exists separately in python/support.py, javascript/support.py, and java/support.py — these are intentional per-language implementations dispatched via the LanguageSupport protocol.

---

Last updated: 2026-04-01

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Codeflash Bot seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}