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cuviper / autocfg

Automatic cfg for Rust compiler features
Apache License 2.0
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autocfg does not work in the presence of -Z build-std #34

Open jdm opened 3 years ago

jdm commented 3 years ago

build.rs:

fn main() {
  assert!(autocfg::new().probe_sysroot_crate("std"));
}

cargo build works fine for any target where libstd is already distributed. cargo build --target x86_64-uwp-windows-msvc -Z build-std panics even though the sysroot is being built correctly.

cuviper commented 3 years ago

Does cargo communicate this in any way? Maybe an environment variable?

jdm commented 3 years ago

I've asked that question in https://rust-lang.zulipchat.com/#narrow/stream/246057-t-cargo/topic/Signalling.20the.20presence.20of.20-Z.20build-std.

melvyn2 commented 1 year ago

This breaks the bigint crate for certain targets like i686-apple-darwin. Any idea for when this might be fixed?

cuviper commented 1 year ago

There's no plan how to fix it yet...

Assuming you mean num-bigint, it should degrade ok without it, no?

melvyn2 commented 1 year ago

Some dependent crates rely on features which get deactivated because of this, even though bigint builds successfully... I'll try to build the stdlib by hand in the meantime. Hopefully -Z build-std will be stabilized eventually.

jyn514 commented 1 year ago

Why does autocfg care if the crate is loaded from the sysroot or passed with --extern? Shouldn't extern crate std work in both cases?

jyn514 commented 1 year ago

Oh, is the problem that cargo only passes --extern std=... to the final crate, not to build scripts? I wonder if it should set some environment variable with a list of the std crates built from source ... in general I think it would be nice for cargo to expose a way for build scripts to invoke rustc the same way cargo would in the current build.

jyn514 commented 1 year ago

Ah, that already exists and it's called CARGO_ENCODED_RUSTFLAGS 😄 I think we should open an upstream issue for cargo to include the --extern std flags in CARGO_ENCODED_RUSTFLAGS.