`undefined reference` to linker error when using from nightly rustc

[fpoli]

In our project we use rustc nightly-2021-10-15 and we encountered a compiler bug that prevents us upgrading from hyper 0.13, warp 0.2, reqwest 0.10, tokio 0.2 to hyper 0.14, warp 0.3, reqwest 0.11, tokio 1.2 (working, not working commit).

It seems that the cause is the C ffi:

hyper/Cargo.toml

Line 23 in 8062714

crate-type = ["lib", "staticlib", "cdylib"]

Removing that line solves the issue: alexkornitzer@1199048

I know that this is not exactly a bug in hyper, but since the C API is unstable I wonder if there is a way to set that crate-type only in the build that generates the C library. At least, until the compiler is fixed.

[seanmonstar]

Unfortunately we currently can't. There's no way for people to enable only a cdylib on-demand. But #2685 is tracking that.

[sfackler]

Couldn't the C interface be moved to a separate crate from hyper itself?

[seanmonstar]

The C interface makes uses of private details, so to use them in a separate crate would require making those "public".

[bjorn3]

An option would be to only expose them when a certain cfg is used. If it is something like foo and not feature = "foo" you can only set it using RUSTFLAGS and not when specifying it as dependency.