fix(js): detect TypeScript transformers beyond ts-jest

[mohammedahmed18]

Problem

When a TypeScript project uses transformers other than ts-jest (e.g., @swc/jest, babel-jest, esbuild-jest), Codeflash generates a Jest config without a transform directive. This causes Jest to fail parsing TypeScript files with syntax errors like "Unexpected token" at type annotations.

Example error:

SyntaxError: /path/to/file.ts: Unexpected token (5:6)
  3 |
  4 | export default class API {
> 5 |   host: string
    |       ^

Root Cause

File: codeflash/languages/javascript/test_runner.py:282-295

The code only checked for ts-jest in package.json and skipped transform configuration when ts-jest was not found, even though other TypeScript transformers might be present:

has_ts_jest = _has_ts_jest_dependency(project_root)

if has_ts_jest:
    transform_config = """..."""
else:
    transform_config = ""  # ← No transform = Jest can't parse TypeScript

Solution

Added _detect_typescript_transformer() function that checks for common TypeScript transformers in order of preference:

1. ts-jest
2. @swc/jest
3. babel-jest (with @babel/preset-typescript)
4. esbuild-jest

When detected, the appropriate transform directive is included in the generated Jest config.

Impact

✅ Fixes: TypeScript projects using @swc/jest (e.g., budibase)
✅ Fixes: TypeScript projects using babel-jest
✅ Fixes: TypeScript projects using esbuild-jest
✅ Maintains: Backward compatibility with ts-jest projects

Testing

• Added test_typescript_transform_extraction.py with two test cases
• All existing test_javascript_test_runner.py tests pass (34 tests)
• Verified fix against budibase trace ID 0acc4768-706a-4fe1-91e6-ec64983bd519

Trace IDs

• 0acc4768-706a-4fe1-91e6-ec64983bd519 - budibase API.patch optimization failure

[claude]

Claude finished @mohammedahmed18's task in 4m 40s —— View job

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PR Review Summary

• Triage PR size (LARGE: ~60 lines production code)
• Lint and typecheck — prek passed; fixed mypy issues in test file
• Resolve stale threads (none)
• Auto-fix and commit style issues
• Review diff
• Duplicate detection

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Prek Checks

Passed. ✅

Auto-fixed and pushed (aa463709):

• Added encoding="utf-8" to read_text() in new _detect_typescript_transformer — required by project convention for all new code
• Removed docstring from _detect_typescript_transformer — project style disallows docstrings in new code unless explicitly requested
• Test file: replaced tempfile.TemporaryDirectory() with tmp_path fixture — project testing convention
• Test file: added -> None return type annotations (mypy errors)
• Test file: removed unused import pytest and class/method docstrings

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Code Review

Bug / Dead Code — must fix

_has_ts_jest_dependency is dead code (test_runner.py:200).

The PR replaces all call sites of _has_ts_jest_dependency with the new _detect_typescript_transformer, but leaves the old function in place. It is now unreachable and should be removed.

Fix this →

Design Issue — consider fixing

Triplicate package.json parsing for ts-jest (test_runner.py:200, 222, 678).

There are now three separate functions that each open package.json and check for ts-jest:

• _has_ts_jest_dependency (dead, see above)
• _detect_typescript_transformer (new — checks deps for 4 transformers)
• _uses_ts_jest (line 678, still actively called at line 737 — also checks jest.config files)

_detect_typescript_transformer and _uses_ts_jest solve overlapping problems: both detect "is ts-jest present?". Consider having _detect_typescript_transformer reuse _uses_ts_jest's result, or consolidate the detection into one function.

Minor — no action needed

The babel-jest detection at line 265 requires both babel-jest and @babel/preset-typescript to be present. This is a reasonable safety guard (babel-jest alone won't handle TypeScript), but it's worth noting as a potential miss if a project uses @babel/preset-typescript via babel.config.js without listing it explicitly in package.json.

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Duplicate Detection

• HIGH confidence: _has_ts_jest_dependency (line 200) vs _detect_typescript_transformer (line 222) — identical package.json parsing pattern, ts-jest detection logic is a strict subset. The former is now dead code.
• MEDIUM confidence: _detect_typescript_transformer (line 222) vs _uses_ts_jest (line 678) — both parse package.json for ts-jest; _uses_ts_jest additionally checks jest.config files.

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Test Coverage

Two integration tests added covering @swc/jest and ts-jest paths. The babel-jest and esbuild-jest branches have no test coverage — acceptable for now but worth noting.

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Last updated: 2026-04-06T11:49Z
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