Add bootstrap check snapshot tests

[Kobzol]

Split off from #143048, so that we get a baseline of how check behaved before we make changes to it. Note that the output of the check snapshot tests is suboptimal in many places, as we're missing information about stages and the build compiler. That will be changed in #143048.

r? @jieyouxu

[rustbot]

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[jieyouxu]

I'm still reviewing the original check PR, I have some review comments for that PR pending before this PR.

EDIT: done a review pass on the original PR, the general direction looks good to me 👍

[jieyouxu]

The initial baseline tests look good; the missing stage numbers on check from what I understand is left as a follow-up.

[jieyouxu]

Suggestion: maybe explicitly spell out the core model here?

Continuing from #143048 (review),

The stage numbering here has two cases:

1. (compiler, library) will receive the same $\mathrm{stage}$ number, because std is necessarily tightly coupled to the compiler.
2. For all other cases, they should be considered $\mathrm{stage} + 1$.

[jieyouxu]

Question: I'm assuming the staging info is intended to be a follow-up (as in the overall PR) right?

As in, I'd expect the derivation chain for this to look like (overly simplified)

$$\prescript{{}}{\text{host}}{\mathrm{LLVM}} \longrightarrow \left\langle \text{compiler}_{\mathrm{0}}^{\mathrm{build}}, \text{library}_{\mathrm{0}}^{\mathrm{build}} \right\rangle \longrightarrow \text{compiler}_{\mathrm{1}}^{\mathrm{check}}$$

[Kobzol]

Yeah. Right now, the check steps implicitly decide which compiler will build them, it's not represented explicitly in their Step parameters. Therefore it's also not easily representable in the step metadata.

[jieyouxu]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[Kobzol]

@rustbot ready

[jieyouxu]

Thanks!

[jieyouxu]

@bors r+ rollup

[bors]

📌 Commit 3f3c498 has been approved by jieyouxu

It is now in the queue for this repository.