rspack-debugging

name	rspack-debugging
description	Debug Rspack crashes, hangs, deadlocks, and coredumps with LLDB-focused workflows. Use when users report segmentation faults, unstable HMR crashes, stuck build/devserver processes, or async deadlocks.

Rspack Debugging

Overview

This Skill guides you on how to capture the underlying crash state of Rspack (which is based on Rust). By using the LLDB debugger and Rspack packages with debug symbols, we can obtain detailed stack backtraces, which are crucial for pinpointing issues. The guides focus on non-interactive, automated debugging to easily capture backtraces.

Preparation

Before starting, please ensure your environment meets the requirements.

1. Install LLDB: You must install the LLDB debugger.

   • macOS: Run xcode-select --install
   • Linux: Install the lldb package (e.g., apt-get install lldb)
   • Detailed guide: references/lldb.md

2. Replace Debug Packages: Production packages like @rspack/core have debug symbols stripped. They must be replaced with the @rspack-debug/* series packages to see useful stack information.

   Automatic Replacement Script:

   bun scripts/setup_debug_deps.cjs
   

   Running the above script will automatically add pnpm.overrides configuration to package.json, pointing Rspack packages to their corresponding Debug versions. Afterwards, please be sure to run pnpm install to update dependencies.

Debugging Workflows

Identify your specific scenario and follow the corresponding linked guide.

Detailed Guides

Guide A: Crash during HMR

Scenario: Stable Crash/Deadlock during DevServer HMR. Read Guide: references/guide_a_hmr_crash.md

Guide B: Crash during Build

Scenario: Stable Crash/Deadlock during Build (or Unstable Build Crash that is frequent enough). Read Guide: references/guide_b_build_crash.md

Guide C: Attach to Stuck Process

Scenario: Unstable Deadlock during Build (happens randomly). Read Guide: references/guide_c_attach_to_stuck_process.md

Guide D: Coredump Analysis (Dev)

Scenario: Unstable Crash during DevServer HMR (hard to catch interactively). Read Guide: references/guide_d_coredump_analysis_dev.md

Guide E: Coredump Analysis (Build)

Scenario: Unstable Crash during Build. Read Guide: references/guide_e_coredump_analysis_build.md

Guide F: Async Deadlock Identification

Scenario: Unstable Async Deadlock. Main thread stuck in uv_run. Read Guide: references/guide_f_async_deadlock.md

Saving Debug Artifacts

Critical Instruction for Agents: When you successfully obtain a backtrace or a tracing log, you MUST save it to a local file in my project directory so it is preserved after the session.

1. Create Directory: Ensure a directory named debug_artifacts exists in the project root.
2. Save Backtraces: Write the full output of thread backtrace all to debug_artifacts/backtrace_<timestamp>.txt.
3. Save Tracing Logs: (Only if using Tracing Skill)

Environment Restoration

After debugging is complete, restore your package.json to use production packages:

bun scripts/setup_debug_deps.cjs --restore
pnpm install