Warn when checking `library/std` when `profile = "compiler"`

[varkor]

I expect these two commands to do the same thing, but for check or build, respectively. However, check may succeed even if build fails type checking. I suspect the syntax for check is a subset of that for build.

[jyn514]

@varkor can you give an example of code that succeeds for check but fails for build?

[varkor]

I edited some code in compiler/rustc_middle/src/infer/canonical.rs. This had a type-checking error in it, but x.py check library/std succeeded. When I ran x.py check (without specifying a path), it emitted an error as expected. x.py build library/std emitted an error with the path specified.

[jyn514]

@varkor I think this is actually related to staging: x.py build library/std builds the stage0 compiler artifacts before building stage1 libstd with the newly built compiler. x.py check always uses stage 0, so x.py check library/std doesn't build the compiler.

[varkor]

@jyn514: x.py check (without the path) emitted the correct error. Does this mean the check stage is affected by the path?

[jyn514]

@varkor yes, the same as build. If you run x.py check compiler/rustc for example, that won't check rustdoc.

[varkor]

@jyn514: are you saying that x.py check library/std will literally only check library/std, using the definitions from the stage0 artefacts, without taking account of the current compiler changes (i.e. those which would be built for stage1)?

[jyn514]

@varkor yes: x.py check library/std is roughly analogous to RUSTFLAGS=--profile=check x.py build --stage 0 library/std. There's not currently a way to check with stage1, although I'd like to add one: #46955 (comment)

[varkor]

Okay, I see. I don't necessarily think there needs to be an option to change the stage: it should just match whatever build does (though this will also take some work to implement).

[jyn514]

@varkor well, if it matches build then you'd have to build the entire compiler before checking the stage 1 standard library, which would double or triple the time. So I don't think stage 1 should be the default.