port-swc-pr

name	port-swc-pr
description	Port a PR from swc-project/swc to this repository, including tests and code changes.

Port SWC PR Skill

This skill guides you through the process of porting a Pull Request from the upstream swc-project/swc repository to the local swc-experimental repository.

Input

• PR ID: The ID of the pull request in swc-project/swc (e.g., 11462).

Workflow

1. Fetch & Analyze Diff

First, retrieve the changes from the upstream PR.

gh pr diff <PR_ID> -R swc-project/swc

Goal: Identify:

1. Test Cases: Look for changes in crates/swc_ecma_parser/tests. Upstream uses snapshot tests.
2. Source Code: Look for changes in crates/swc_ecma_parser/src.

Create a git branch named like 02-01-feat/port-1234, where feat should be respected to the type of change in the source PR.

2. Port Test Cases (First Step)

Rule: Always match the test failure before fixing the code.

1. Locate Target Directory: Tests in this repo are stored in tasks/testsuite/fixtures/misc-parser.

   • Passing Tests (Should parse successfully): tasks/testsuite/fixtures/misc-parser/pass
   • Failing Tests (Should fail parsing): tasks/testsuite/fixtures/misc-parser/fail

2. Create Test File:

   • Naming: Create a single file in tasks/testsuite/fixtures/misc-parser/{pass,fail}.
   • Filename: Derive the filename from the upstream test path to be descriptive (e.g., if upstream is tests/foo/bar.js, name it bar.js or foo-bar.js).
   • Content: Copy the JavaScript code from the upstream snapshot/test.

3. Run Tests (Expect Failure): Run the test suite to confirm the tests fail (or behave incorrectly) without the fix.

   cargo run -p testsuite
   

   Verify that your new test case is failing.

3. Port Source Code

Apply the logic changes from the diff to the local codebase.

File Mapping Guide: The local repository structure differs slightly from upstream. Use this mapping as a reference:

• Upstream crates/swc_ecma_parser/src/parser/*.rs -> Local crates/swc_ecma_parser/src/parser/js/*.rs
  • Example: src/parser/expr.rs -> src/parser/js/expr.rs
  • Example: src/parser/stmt.rs -> src/parser/js/stmt.rs

Instructions:

1. Read the upstream code changes carefully.
2. Find the equivalent code in the mapped local file.
3. Apply the changes, adapting variable names and internal struct logic if necessary.

4. Verify Fix

Run the test suite again to verify the fix.

cargo run -p testsuite

• Pass: The test case should now pass (or fail gracefully if it's a negative test).
• Fail: If it still fails, debug the local implementation.

5. Submit PR

Once the tests pass and the code is verified:

1. Get Upstream Title:

   gh pr view <PR_ID> -R swc-project/swc --json title --jq .title
   

2. Create PR: Create the PR using the upstream title and referencing the upstream PR ID in the body.

   gh pr create --title "<UPSTREAM_TITLE>" --body "Port of <PR_ID>"
   

Tips

• File Structure: Use find_by_name if you can't locate a file.
• Run Specific Tests: The testsuite might run all tests. If it's too slow, check if cargo run -p testsuite -- --help offers filtering options (e.g., matching the filename).