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

• the MCP
• the implementation PR
• the Zulip stream