Rust 1.42.0 can't compile Rust 1.42.0

[thomasjfox]

Hello together,

compiling Rust 1.42.0 with Rust 1.42.0 results in this error early on:

   Compiling bootstrap v0.0.0 (/datastore/rpmbuild/BUILD/rustc-1.42.0-src/src/bootstrap)                                                                      
error: unnecessary parentheses around block return value                       
    --> src/bootstrap/lib.rs:1029:9                                                                                                                           
     |                                                                                                                                                        
1029 |         (target.contains("linux-gnu") || target.contains("apple-darwin"))                                                                              
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove these parentheses                                               
     |                                                                                                                                                        
     = note: `-D unused-parens` implied by `-D warnings`                                                                                                      
                                                                                                                                                              
error: aborting due to previous error                                                                                                                         
                                                                                                                                                              
error: could not compile `bootstrap`.

I'm now going to test this fix:
5f979e9#diff-6710e3160b86e8cc371d2ff58ae1061c

The compiler was built with Rust 1.41.1.
I always do the "Rustception" test ;)

[cuviper]

I'm now going to test this fix:
5f979e9#diff-6710e3160b86e8cc371d2ff58ae1061c

That change can also be found in 31dcdc9#diff-6710e3160b86e8cc371d2ff58ae1061c, part of the PR when the master branch updated bootstrap to 1.42-beta.

[Mark-Simulacrum]

Hm, I wonder if we should disable deny-warnings by default if we're not in a git repository or so -- in practice I think it's true there's nothing we could have done to prevent this? i.e., rust-lang/rust needs the parens gone to be able to bootstrap.

[cuviper]

in practice I think it's true there's nothing we could have done to prevent this? i.e., rust-lang/rust needs the parens gone to be able to bootstrap.

I'd still like to see something like distcheck for this -- e.g. use the result of a build as the stage0 of a new build. Even just ./x.py check that way would have caught this, I think. At least the removed parens are still compatible either way, so we don't have a dilemma between old and new.

[Mark-Simulacrum]

Yes, I think it's true that we could catch this -- I'm less concerned about the "how to know this will happen," but more concerned about the fact that keeping code around to support self-bootstrap may not be viable in all cases (e.g., we used to and perhaps still use bootstrap libtest in compiletest or something like that).

OTOH, I believe it is true that such a check would push us to make sure that we bootstrap appropriately which should also always be possible.

[thomasjfox]

A similar issue has already been discussed previously:
"Rust 1.33 stable fails to compile itself" #58845

Either way, the linked patch fixes the (trivial) issue.

Rust 1.42.0 compiles all the crates I've stored locally, good job with the release!

[cuviper]

(e.g., we used to and perhaps still use bootstrap libtest in compiletest or something like that).

#68019 switched that to in-tree libtest, but lang differences still apply, like this paren warning.

@thomasjfox yeah, I thought I had suggested such a distcheck before... just need someone to get around to it, I guess, assuming we have a little bit of CI budget for the task.

[Keruspe]

1.42.0 compiles 1.42.0 just fine here if deny-warnings = false

[infinity0]

FWIW we set --cap-lints warn in all Debian rust builds by default to avoid this general problem, since it occasionally occurs in random crates not just rustc itself.

[jonas-schievink]

Closing since 1.43 is now released and there's a workaround if you still need to build 1.42