redesign stage 0 std

[onur-ozkan]

This is intended to update bootstrap to use the beta standard library on stage 0, rather than compiling it from source (see the motivation at rust-lang/compiler-team#619).

Blocked on #122709

[rustbot]

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

[onur-ozkan]

@rustbot ready

r? bootstrap
cc @rust-lang/libs

[onur-ozkan]

@rustbot author (currently stage 2 std is copied from stage 1 and this behaviour should change with the beta std change)

[onur-ozkan]

I am waiting for the next beta release. Right now compiler depending on some nightly features which will be resolved with the next beta release.

[RalfJung]

That's a concern for this plan, isn't it? We'll lose the ability to immediately depend on nightly library features; we'll need to wait for a bootstrap bump. We should at least know how much we relied on that in the past to get an idea of how disruptive that will be.

[onur-ozkan]

It is a concern yes. From what I learned (source), it happened very few times in the past.

[RalfJung]

What nightly API is causing the trouble right now?

[onur-ozkan]

What nightly API is causing the trouble right now?

This and several other functions in the same module uses ptr_sub_ptr nightly feature.

[bjorn3]

With this PR is

rust/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh

Line 212 in a21d978

COMPILETEST_FORCE_STAGE0=1 ./x.py test --stage 0 --test-args=--no-capture tests/{codegen-units,run-make,ui,incremental}

still enough to test the bootstrap compiler rather than build rustc and then test that rustc?

[onur-ozkan]

With this PR is

rust/compiler/rustc_codegen_cranelift/scripts/test_rustc_tests.sh

Line 212 in a21d978

COMPILETEST_FORCE_STAGE0=1 ./x.py test --stage 0 --test-args=--no-capture tests/{codegen-units,run-make,ui,incremental}

still enough to test the bootstrap compiler rather than build rustc and then test that rustc?

It will still be enough to test the bootstrap compiler; the only difference is that the stage0 library will be the beta library, not the in-tree one.

[bjorn3]

Great! That will save some time and avoids the need to apply the standard library patches to the rust checkout too. The bootstrap compiler for me matches the rust checkout except with cg_clif as codegen backend.

[RalfJung]

This and several other functions in the same module uses ptr_sub_ptr nightly feature.

Ah, that is an API that was recently renamed and then stabilized. Given that this will happen again, it seems worth ensuring that this keeps working. It should work with some cfg(bootstrap) in that code, right?

[onur-ozkan]

It's unstable in the beta std, that's why it's not working with cfg bootstrap.

[RalfJung]

That just means the compiler needs a cfg_attr(bootstrap, feature(...))?

If this does not worth with cfg bootstrap we have a problem; something like this must be supported.

[onur-ozkan]

Actually, we can make that work with RUSTC_BOOTSTRAP, I forgot about that...

[bors]

☔ The latest upstream changes (presumably #138083) made this pull request unmergeable. Please resolve the merge conflicts.