Debugging#

Debugging with VS Code#

1. Install go install github.com/go-delve/delve/cmd/dlv@latest
2. Install VS Code extension rust-analyzer and CodeLLDB
3. build @rspack/cli and napi binding by run pnpm install && pnpm -w build:cli:debug
4. In VS Code's Run and Debug tab, select debug-rspack to start debugging the initial launch of @rspack/cli. This task can be configured in .vscode/launch.json, which launches the Node and Rust debugger together.

Tracing#

tracing is used to instrumenting Rspack.

The supported tracing levels for

• release builds are INFO, WARN and ERROR
• debug builds are TRACE, DEBUG, INFO, WARN and ERROR

Use the RSPACK_PROFILE environment variable for displaying trace information

RSPACK_PROFILE=TRACE=layer=logger rspack build
# filter for an event
RSPACK_PROFILE='TRACE=layer=logger&filter=rspack_core::compiler::compilation' rspack build
# with logger level
RSPACK_PROFILE='TRACE=layer=logger&filter=rspack_core::compiler::compilation=info' rspack build
# filter logs across multiple modules
RSPACK_PROFILE='TRACE=layer=logger&filter=rspack_core::compiler::compilation,rspack_core::build_chunk_graph::code_splitter' rspack build
# [fn_name] will show:
# - all functions calls to `fn_name`
# - the arguments(except for these in the `skip` list)
# - everything until this function returns
RSPACK_PROFILE='TRACE=layer=logger&filter=[build_chunk_graph]' rspack build
# compilation::chunk_asset is a custom instrument name
RSPACK_PROFILE='TRACE=layer=logger&filter=[compilation:chunk_asset]' rspack build
# log a specific function by their arguments
RSPACK_PROFILE='TRACE=layer=logger&filter=[compilation:chunk_asset{filename="main\.js"}]' rspack build
# It support regexp expression
RSPACK_PROFILE='TRACE=layer=logger&filter=[compilation:chunk_asset{filename=".*\.js"}]' rspack build
# disable ansi color escape codes
NO_COLOR=1 RSPACK_PROFILE=TRACE=layer=logger rspack build

Resolver#

rspack_resolver emits some tracing information for debugging purposes.

RSPACK_PROFILE='TRACE=filter=rspack_resolver=trace&layer=logger' rspack build

rust-lldb#

rust-lldb can be used to get panic information from debug builds

rust-lldb -- node /path/to/rspack build

Once it launches, press r for running the program.

For example, examples/arco-pro crashes without any information before this fix:

Using rust-lldb

rspack/examples/arco-pro ❯ rust-lldb -- node ../../packages/rspack-cli/bin/rspack build

Press r and it prints:

Mixed Debug#

This section aims to illustrate the method for mixed debugging between JavaScript and Rust.

Prerequisites#

To illustrate this process, I'll use an example. Let's start by introduce the environment and example I have used.

• System: macos
• IDE: vscode
• Debugging target: rspack build ${projectRoot}/basic

Firstly, you need to build rspack in debug mode. To do this, execute the following commands in the project's root directory:

npm run build:binding:debug
npm run build:js

Configure launch.json in VS Code#

It's necessary to configure two debug configurations within in .vscode/launch.json.

• attach for node:

{
  "name": "attach:node",
  "request": "attach", // refer: https://code.visualstudio.com/docs/editor/debugging#_launch-versus-attach-configurations
  "type": "node",
  // `9229` is the default port of message
  "port": 9229,
}

• and launch for lldb

{
  "name": "launch:rust-from-node",
  "request": "launch",
  "type": "lldb", // it means we use `lldb` to launch the binary file of `node`
  "program": "node",
  "args": [
    "--inspect",
    "--enable-source-maps",
    "${workspaceFolder}/packages/rspack-cli/bin/rspack",
    "build",
    "-c",
    "${workspaceFolder}/examples/basic/rspack.config.js",
  ],
  // `cwd` is just for repack find the correctly entry.
  "cwd": "${workspaceFolder}/examples/basic/",
}

Next, we can utilize compounds to amalgamate the two commands:

{
  "name": "mix-debug",
  "configurations": ["attach:node", "launch:rust-from-node"]
}

Finally, your launch.json should appear as follows:

{
  "configurations": [
    {
      "name": "attach:node",
      "request": "attach",
      "type": "node",
      "port": 9229
    },
    {
      "name": "launch:rust-from-node",
      "request": "launch",
      "type": "lldb",
      "program": "node",
      "args": [
        "--inspect",
        "--enable-source-maps",
        "${workspaceFolder}/packages/rspack-cli/bin/rspack",
        "build",
        "-c",
        "${workspaceFolder}/examples/basic/rspack.config.js"
      ],
      "cwd": "${workspaceFolder}/examples/basic/"
    }
  ],
  "compounds": [
    {
      "name": "mix-debug",
      "configurations": ["attach:node", "launch:rust-from-node"]
    }
  ]
}

Debugging Attempt#

Next, we can introduce some breakpoints and commence debugging.

The result appears as follows: