Agent skill

fix-bug

Systematic bug fixing workflow with regression tests and PR creation. Use when the user asks to "fix a bug", "debug an issue", "resolve a problem", or provides error messages/failing tests to fix. Handles reproduction, root cause analysis, test creation, fix implementation, and PR submission.

View SKILL.md on GitHub Repository
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Forks 31

Install this agent skill to your Project

npx add-skill https://github.com/majiayu000/claude-skill-registry/tree/main/skills/other/other/fix-bug-milky2018-wasmoon

SKILL.md

Fix Bug Workflow

Systematic approach to fixing bugs with proper testing and documentation.

Workflow

1. Reproduce the Bug

Run the provided command or test to observe the failure:

bash
# For WAST tests
./wasmoon test <file>.wast

# For MoonBit tests
moon test -p <package> -f <file>.mbt

# For specific test by index
moon test -p <package> -f <file>.mbt -i <index>

Document:

  • Error messages
  • Stack traces
  • Expected vs actual behavior
  • Steps to reproduce

2. Analyze Root Cause

Investigate the error systematically:

a) Examine error messages

  • Identify the failing component
  • Note line numbers and function names

b) Locate relevant code

  • Use Glob to find implementation files: **/*<keyword>*.mbt
  • Use Grep to search for specific functions or patterns
  • Read source code in relevant modules

c) For WASM-related bugs

bash
./wasmoon explore <file>.wat --stage ir vcode mc

Check IR, VCode, and machine code for issues.

d) For crashes or segfaults

bash
lldb -- ./wasmoon test <file>.wast
(lldb) run
(lldb) bt  # After crash

3. Create Regression Test

Before fixing, write a test that reproduces the bug:

For WASM execution bugs:

moonbit
test "descriptive_bug_name" {
  let source =
    #|(module
    #|  (func (export "test") (result i32)
    #|    ; Bug-reproducing code here
    #|  )
    #|)
  let result = compare_jit_interp(source, "test", [])
  inspect(result, content="matched")
}

For unit tests:

moonbit
test "descriptive_bug_name" {
  let result = buggy_function(input)
  inspect(result, content="expected_value")
}

Place the test in the appropriate *_test.mbt file in the relevant package.

Verify the test fails:

bash
moon test -p <package> -f <test_file>.mbt

4. Implement Fix

Make the necessary code changes:

  • Fix the root cause, not just symptoms
  • Follow coding standards (see ERRATA.md and CLAUDE.md)
  • Keep changes minimal and focused
  • Avoid refactoring unless necessary

Run tests to verify:

bash
moon test -p <package>      # Unit tests
moon test                    # All tests
moon build && ./install.sh  # For wasmoon binary changes

5. Verify No Regressions

Ensure the fix doesn't break other functionality:

bash
moon test                    # All unit tests
python3 scripts/run_all_wast.py --rec  # All wast tests

6. Create Pull Request

a) Create feature branch

bash
git checkout -b fix/<descriptive-name>

b) Commit changes

bash
moon fmt && moon info
git add .
git commit -m "$(cat <<'EOF'
fix: <brief description>

- Root cause: <explanation>
- Solution: <what was changed>
- Test: <test that verifies the fix>

EOF
)"

c) Push and create PR

bash
git push -u origin fix/<descriptive-name>
gh pr create --title "fix: <brief description>" --body "$(cat <<'EOF'
## Summary
- Root cause: <explanation>
- Solution: <what was changed>
- Test: <test file and description>

## Test Plan
- [ ] Regression test passes
- [ ] All existing tests pass
- [ ] Manual verification of fix

EOF
)"

Best Practices

  • Always create a regression test before fixing
  • Keep fixes minimal and focused
  • Test both the fix and potential regressions
  • Document the root cause in commit messages
  • Follow project commit message conventions
  • Never use commit --amend or push --force on shared branches

Command Reference

bash
# Build and install
moon build && ./install.sh

# Run tests
moon test -p <package> -f <file>.mbt
moon test -p <package> -f <file>.mbt -i <index>

# Analyze WASM
./wasmoon explore <file>.wat --stage ir vcode mc
./wasmoon test <file>.wast
./wasmoon test --no-jit <file>.wast

# Debug with LLDB
lldb -- ./wasmoon test <file>.wast

# Git workflow
git checkout -b fix/<name>
git add . && git commit
git push -u origin fix/<name>
gh pr create

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