Changes to x.py defaults

Aug. 30, 2020 · Jynn Nelson on behalf of the compiler team

Recently, the defaults for x.py, the tool used to bootstrap the Rust compiler from source, changed. If you regularly contribute to Rust, this might affect your workflow.

What changes were made?

  • The default stage is now dependent on the subcommand:

    • dist: stage 2
    • build: stage 1
    • test: stage 1
    • doc: stage 0

  • stage 1 rustc artifacts are no longer built by x.py build --stage 1. To get the old behavior back, use x.py build --stage 1 src/rustc. The new behavior for build --stage 1 builds everything except rustc, which includes the standard library, rustdoc, and various other tools (if the tools are enabled).

  • debuginfo now defaults to 1 when debug = true. Previously, the default was 2.

Why were the changes made?

Previously, x.py build would build rustc twice:

  1. build/stage0-std
  2. build/stage0-rustc
  3. build/stage1-std
  4. build/stage1-rustc

Normally, contributors only want to build the compiler once, which lets them test their changes quickly. After this change, that's now the default:

  1. build/stage0-std
  2. build/stage0-rustc
  3. build/stage1-std

debuginfo = 2 generates several gigabytes of debug information, making the previous default settings for debug = true very painful.

For a detailed rationale of the changes, as well as more information about the alternatives considered, see