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Nov 11, 2025
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update the bootstrap readme #148530

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ebe6c4c
update the bootstrap readme
Shourya742 Nov 9, 2025
425c704
use consistent terminology here. It might not be beta if we overrode …
Shourya742 Nov 10, 2025
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22 changes: 11 additions & 11 deletions src/bootstrap/README.md
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Expand Up @@ -28,14 +28,14 @@ compiler. What actually happens when you invoke bootstrap is:
`x.py` cross-platform) is run. This script is responsible for downloading the stage0
compiler/Cargo binaries, and it then compiles the build system itself (this folder).
Finally, it then invokes the actual `bootstrap` binary build system.
2. In Rust, `bootstrap` will slurp up all configuration, perform a number of
sanity checks (whether compilers exist, for example), and then start building the
stage0 artifacts.
3. The stage0 `cargo`, downloaded earlier, is used to build the standard library
and the compiler, and then these binaries are then copied to the `stage1`
directory. That compiler is then used to generate the stage1 artifacts which
are then copied to the stage2 directory, and then finally, the stage2
artifacts are generated using that compiler.
2. In Rust, the bootstrap binary reads all configuration, performs a number of sanity
checks (for example, verifying toolchains and paths), and then prepares to build the
stage 1 compiler and libraries using the prebuilt stage 0 compiler.
3. The stage 0 compiler and standard library, downloaded earlier, are used to build the
stage 1 compiler, which links against the stage 0 standard library. The newly built stage 1
compiler is then used to build the stage 1 standard library. After that, the stage 1
compiler is used once more to produce the stage 2 compiler, which links against the
stage 1 standard library.

The goal of each stage is to (a) leverage Cargo as much as possible and failing
that (b) leverage Rust as much as possible!
Expand Down Expand Up @@ -167,7 +167,6 @@ build/
# no extra build output in these directories.
stage1/
stage2/
stage3/
```

## Extending bootstrap
Expand All @@ -177,8 +176,9 @@ When you use bootstrap, you'll call it through the entry point script
`bootstrap` has a difficult problem: it is written in Rust, but yet it is run
before the Rust compiler is built! To work around this, there are two components
of bootstrap: the main one written in rust, and `bootstrap.py`. `bootstrap.py`
is what gets run by entry point script. It takes care of downloading the `stage0`
compiler, which will then build the bootstrap binary written in Rust.
is what gets run by entry point script. It takes care of downloading the prebuilt
stage 0 compiler, std and Cargo binaries, which are then used to build the
bootstrap binary.

Because there are two separate codebases behind `x.py`, they need to
be kept in sync. In particular, both `bootstrap.py` and the bootstrap binary
Expand Down
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