`x check --stage 1 std` doesn't work

[WaffleLapkin]

For me currently x b --stage 1 library/std works fine, while x c --stage 1 library/std with a lot of errors related to core not being found.

error: could not compile ppv-lite86 due to 750 previous errors
error: could not compile test due to 60 previous errors
error: could not compile proc_macro due to 2 previous errors

This is the commit that I'm trying to check: c68cd2f

I had the same problem previously too, but it usually solves magically after rebase / x clean / etc. However the usual "reboot router" kind of solutions doesn't seem to help this time :')

Full output: log.txt

[ehuss]

It's not really clear to me how #81064 was supposed to work, but commenting out this line makes it work for me.

[jyn514]

Found the issue. I broke this when I added --all-targets in #88094. Not exactly sure why it's breaking, but it seems fine to me to only run --all-targets in stage 0.

Mentoring instructions: change

rust/src/bootstrap/check.rs

Line 143 in 601c5a2

cargo.arg("--all-targets");

to only run in stage 0.

[jyn514]

It's not really clear to me how #81064 was supposed to work, but commenting out this line makes it work for me.

The way it works is by building all of libstd before checking the compiler:

rust/src/bootstrap/check.rs

Lines 195 to 202 in 601c5a2

	if compiler.stage != 0 {
	// If we're not in stage 0, then we won't have a std from the beta
	// compiler around. That means we need to make sure there's one in
	// the sysroot for the compiler to find. Otherwise, we're going to
	// fail when building crates that need to generate code (e.g., build
	// scripts and their dependencies).
	builder.ensure(crate::compile::Std::new(compiler, compiler.host));
	builder.ensure(crate::compile::Std::new(compiler, target));

That works fine and makes it ok not to call add_to_sysroot in check, but the same step is missing before checking tests and examples. That would be an alternate fix; call builder.ensure(compile::Std) before --all-targets, not just before building the compiler.

[jyn514]

Hmm, I wonder if we should start using --extern noprelude:core in bootstrap to avoid all these sysroot shenanigans. It would make the code a lot simpler I think, and avoid having to compile things twice.

[jo3bingham]

@rustbot claim

[jo3bingham]

@jyn514 is the fix here to still only run --all-targets in stage0, or is your latest comment a better solution? If the latter, is that an easy solution? This is my first contribution to rust so I'm not well versed on how bootstrap, or anything else for that matter, works.

[jyn514]

@jo3bingham my second comment is a harder but more correct solution. I would accept either as PRs, neither are terribly hard.

(My third comment about sysroots I think is the ideal solution, but involves several large refactors to bootstrap and isn't a good first PR.)

[jyn514]

Take a look at the bootstrapping section of the dev guide, especially the bit about contributing: https://rustc-dev-guide.rust-lang.org/building/bootstrapping.html#contributing-to-bootstrap