Mark repr128 as incomplete_features

[varkor]

As mentioned in #56071 and noticed in #77457, repr(u128) and repr(i128) do not work properly due to lack of LLVM support. We should thus warn users trying to use the feature that they may encounter ICEs when using it.

Closes#77457.

[rust-highfive]

r? @eddyb

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[jonas-schievink]

@bors r+

[bors]

📌 Commit db0438b has been approved by jonas-schievink

[RalfJung]

With PRs like this, it is rather unfortunate that the stdlib sets #![allow(incomplete_features)]... I suppose that's mostly due to const generics, so it'll be hard to do anything about this?

[varkor]

I suppose that's mostly due to const generics, so it'll be hard to do anything about this?

I believe so. It's possible some of the uses may only require min_const_generics, which would avoid this problem. It could be worth trying to switch.

[JohnTitor]

Failed in https://github.com/rust-lang-ci/rust/runs/1243760569:

---- compile_test stdout ----
thread 'compile_test' panicked at 'Some tests failed', /cargo/registry/src/github.com-1ecc6299db9ec823/compiletest_rs-0.5.0/src/lib.rs:105:22
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
failures:
compile_test
test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
error: test failed, to rerun pass '--test compile-test'
command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "test" "--target" "x86_64-unknown-linux-gnu" "-Zbinary-dep-depinfo" "-j" "16" "--release" "--locked" "--color" "always" "--manifest-path" "/checkout/src/tools/clippy/Cargo.toml" "--features" "rustc-workspace-hack/all-static" "--"
expected success, got: exit code: 101
failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test --stage 2 src/tools/clippy

Seems some tests on clippy also need a tweak.
@bors r-

[bors]

☔ The latest upstream changes (presumably #77124) made this pull request unmergeable. Please resolve the merge conflicts.

Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels:

@rustbot modify labels: +S-waiting-on-review -S-waiting-on-author

[varkor]

@bors r=jonas-schievink

[bors]

📌 Commit 683db31 has been approved by jonas-schievink