libstd, liballoc_jemalloc fail to build with xargo due to use of deprecated gcc::Config

[RalfJung]

Trying to build the latest libstd outside of the rustc build itself (i.e., using xargo and the rust-src component) results in warnings and build failures:

warning: use of deprecated item: gcc::Config has been renamed to gcc::Build
    --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/rustc/compiler_builtins_shim/../../libcompiler_builtins/build.rs:4011:24
     |
4011 |         let cfg = &mut gcc::Config::new();
     |                        ^^^^^^^^^^^^^^^^
     |
     = note: #[warn(deprecated)] on by default

error: use of deprecated item: gcc::Config has been renamed to gcc::Build
  --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/build.rs:80:20
   |
80 |     let compiler = gcc::Config::new().get_compiler();
   |                    ^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/build.rs:11:9
   |
11 | #![deny(warnings)]
   |         ^^^^^^^^
   = note: #[deny(deprecated)] implied by #[deny(warnings)]

error: use of deprecated item: gcc::Config has been renamed to gcc::Build
  --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc_jemalloc/build.rs:66:20
   |
66 |     let compiler = gcc::Config::new().get_compiler();
   |                    ^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc_jemalloc/build.rs:11:9
   |
11 | #![deny(warnings)]
   |         ^^^^^^^^
   = note: #[deny(deprecated)] implied by #[deny(warnings)]

error: use of deprecated item: gcc::Config has been renamed to gcc::Build
   --> /home/r/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc_jemalloc/build.rs:173:9
    |
173 |         gcc::Config::new()
    |         ^^^^^^^^^^^^^^^^

I think what happens is that the lock file in rustc itself makes rustc still use an older version of the gcc crate, but since that crate deprecated gcc::Config in a minor release, and since some crates in rustc have deny(warnings), the gcc minor version upgrade breaks the build here. libstd's Cargo.toml says gcc = "0.3.50", so cargo will happily use 0.3.52 instead.

I tried fixing this by using gcc::Build rather than gcc::Config in rustc itself, but then it complains that there is no Build in gcc. Seems like I have to find some way to upgrade the version of the gcc crate that rustc uses?

Cc @alexcrichton

[ids1024]

I noticed this too. I guess xargo is ignoring Rust's Cargo.lock file? Perhaps that is something that should be fixed in xargo.

Of course, the crate should be updated anyway, but that might prevent future issues (although it isn't a common issue).

[RalfJung]

The Cargo.lock is not part of the rust-src tarball, so xargo has no way to know which version rustc used.

[ids1024]

Oh; in that case, perhaps the Cargo.lock file should be added to rust-src as well.

Again this isn't a common issue, so it's perhaps not that important; but including Cargo.lock in rust-src and having xargo respect it is probably "correct" behavior.

[RalfJung]

@ids1024 You may like this: japaric/xargo#166