Consistently unset RUSTC_BOOTSTRAP when compiling bootstrap

[dtolnay]

Since #113906, all x.py invocations performed by rust-analyzer have RUSTC_BOOTSTRAP=1 set. This was to fix #112391 (comment) — rust-analyzer uses some default cargo from the system when fetching workspace layout, and the standard library uses some unstable cargo feature, so x.py would previously fail if the system toolchain wasn't nightly.

rust/library/std/Cargo.toml

Line 1 in 82e1608

cargo-features = ["public-dependency"]

This PR changes x.py to cancel out this RUSTC_BOOTSTRAP=1 when compiling bootstrap. It will only remain set when running the compiled bootstrap executable. This fixes spurious bootstrap rebuilds in the event that a rust-analyzer x.py invocation is alternated with someone running x.py themself on the command line, if any dependency of bootstrap looks at option_env!("RUSTC_BOOTSTRAP"), which is the case since #119654.

Before:

$ RUSTC_BOOTSTRAP=1 ./x.py check library/core
Building bootstrap
   Compiling proc-macro2 v1.0.76
   Compiling quote v1.0.35
   Compiling syn v2.0.48
   Compiling clap_derive v4.4.7
   Compiling serde_derive v1.0.195
   Compiling clap v4.4.13
   Compiling clap_complete v4.4.6
   Compiling build_helper v0.1.0
   Compiling bootstrap v0.0.0
    Finished dev [unoptimized] target(s) in 6.31s
Checking stage0 library artifacts {core} (x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.23s
Build completed successfully in 0:00:07

$ ./x.py check library/core
Building bootstrap
   Compiling proc-macro2 v1.0.76
   Compiling quote v1.0.35
   Compiling syn v2.0.48
   Compiling clap_derive v4.4.7
   Compiling serde_derive v1.0.195
   Compiling clap v4.4.13
   Compiling clap_complete v4.4.6
   Compiling build_helper v0.1.0
   Compiling bootstrap v0.0.0
    Finished dev [unoptimized] target(s) in 5.30s
Checking stage0 library artifacts {core} (x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.25s
Build completed successfully in 0:00:06

After:

$ RUSTC_BOOTSTRAP=1 ./x.py check library/core
Building bootstrap
    Finished dev [unoptimized] target(s) in 0.06s
Checking stage0 library artifacts {core} (x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.14s
Build completed successfully in 0:00:01

$ ./x.py check library/core
Building bootstrap
    Finished dev [unoptimized] target(s) in 0.04s
Checking stage0 library artifacts {core} (x86_64-unknown-linux-gnu)
    Finished release [optimized] target(s) in 0.13s
Build completed successfully in 0:00:01

[rustbot]

r? @clubby789

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[onur-ozkan]

@bors r+

[bors]

📌 Commit ee370a1 has been approved by onur-ozkan

It is now in the queue for this repository.

[compiler-errors]

@bors rollup

[petrochenkov]

I think this just broke building everything with -Zthreads=8 - https://internals.rust-lang.org/t/rust-compiler-with-parallel-build/20099
If RUSTC_BOOTSTRAP was set externally, then it should not be removed.

[onur-ozkan]

I think this just broke building everything with -Zthreads=8 - https://internals.rust-lang.org/t/rust-compiler-with-parallel-build/20099

Correct.

If RUSTC_BOOTSTRAP was set externally, then it should not be removed.

I think setting it consistently is much better approach (or if it wasn't manually set from user). What do you think ? @dtolnay

[dtolnay]

I think setting it consistently is much better approach (or if it wasn't manually set from user). What do you think ? @dtolnay

I agree with this, but responded in #120096 (review) with one modification I would suggest.