Get rid of a warning

[tea]

I get this error when building the crate using fresh rust:

error: `extern crate` is not idiomatic in the new edition
   --> /home/aturkin/redox/compiler-builtins/build.rs:225:5
    |
225 |     extern crate cc;
    |     ^^^^^^^^^^^^^^^^
    |
    = note: `-D unused-extern-crates` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unused_extern_crates)]`
help: convert it to a `use`
    |
225 |     use cc;
    |     ~~~

Indeed 2018 edition documentation says extern crate should not be used anymore "in 99% of circumstances". So this PR follows the advice.

[Amanieu]

The use isn't even necessary: crate names are always automatically imported.

[tea]

The use isn't even necessary: crate names are always automatically imported.

Removed now. CI is failing due to some seemingly unrelated stuff.

[tgross35]

Could you try setting edition = 2021 in crates/panic-handler/Cargo.toml? That is an interesting failure

[tgross35]

You can probably change to edition = 2021 in the root Cargo.toml too, I don't think we have any reason to stay on 2018

[tea]

Could you try setting edition = 2021 in crates/panic-handler/Cargo.toml? That is an interesting failure

No dice.

[tgross35]

Oh nevermind, this is just a new lint in the latest nightly rust-lang/rust@c4c7859. Looks like lines 135 and 263 try to use define_rust_probestack but the macro cfged out on the relevant platforms.

To match the current behavior you could add another define_rust_probestack macro that returns nothing and has cfg to only be available on the platforms that are missing it (really a better job for cfg_if but we don't have that).

Even if that matches the current behavior though, it might not be the intended behavior (Amanieu will know)

edit: doesn't look like any cfg patterns are missing after all

[tea]

Oh nevermind, this is just a new lint in the latest nightly rust-lang/rust@c4c7859. Looks like lines 135 and 263 try to use define_rust_probestack but the macro cfged out on the relevant platforms.

That is weird. The macro is defined within the same file; entire file is only cfged in for x86/x64, and conditionals on the 4 macro defines seem to cover every possible target.

Anyway, this is a bit above my head (I'm just learning Rust so decided to do a light deep immersion by trying to add risc-v support to Redox; just doing something easy, y'know :)).

[tgross35]

That is weird. The macro is defined within the same file; entire file is only cfged in for x86/x64, and conditionals on the 4 macro defines seem to cover every possible target.

It is weird, the new lint might just be wrong. I asked at rust-lang/rust#126984.

Anyway, this is a bit above my head (I'm just learning Rust so decided to do a light deep immersion by trying to add risc-v support to Redox; just doing something easy, y'know :)).

You should probably be able to just do what it suggests and add #![allow(out_of_scope_macro_calls)] to the top of the file so the warning doesn't show up, we can figure out the cause later.

Quite the light deep immersion indeed, welcome to Rust :)