`error: cannot satisfy dependencies so ... only shows up once` when linking `rustc_driver` since #122362

[tamird]

Code

I tried this code:

src/lib.rs:

#![feature(rustc_private)]

extern crate rustc_driver;
extern crate rustc_session;

#[rustversion::since(2024-11-03)]
use rustc_session::config::host_tuple as rustc_host;

#[rustversion::before(2024-11-03)]
use rustc_session::config::host_triple as rustc_host;

pub fn host() -> &'static str {
    rustc_host()
}

tests/integration_test.rs:

#[test]
fn test_target_tuple() {
    assert_ne!(
        testing_integration_rustc_private::host(),
        "unknown-unknown-unknown"
    );
}

I expected to see this happen: cargo +nightly test succeeds.

Instead, this happened:

$ cargo +nightly test

   Compiling testing-integration-rustc-private v0.1.0 (/Users/tamird/src/testing-integration-rustc-private)
error: cannot satisfy dependencies so `rustc_driver` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = note: `rustc_driver` was unavailable as a static crate, preventing fully static linking
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `core` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `compiler_builtins` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `rustc_std_workspace_core` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `alloc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `libc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `unwind` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `cfg_if` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `miniz_oxide` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `adler` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `hashbrown` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `rustc_std_workspace_alloc` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `std_detect` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `rustc_demangle` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `addr2line` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `gimli` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `object` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `memchr` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: cannot satisfy dependencies so `panic_unwind` only shows up once
  |
  = help: having upstream crates all available in one format will likely make this go away
  = help: `feature(rustc_private)` is needed to link to the compiler's `rustc_driver` library

error: could not compile `testing-integration-rustc-private` (test "integration_test") due to 19 previous errors

Version it worked on

Using cargo-rustc-bisect:

searched nightlies: from nightly-2024-08-05 to nightly-2024-12-27                                                                                                         
regressed nightly: nightly-2024-08-12                                                                                                                                     
searched commit range: https://github.com/rust-lang/rust/compare/730d5d4095a264ef5f7c0a0781eea68c15431d45...41dd149fd6a6a06795fc6b9f54cb49af2f61775f
regressed commit: https://github.com/rust-lang/rust/commit/9cb1998ea15e179482504e07cad8fa121e169a32

This points to #122362 (9cb1998).

[bjorn3]

You need to add #![feature(rustc_private)] to the test crate too. The presence of the feature gate changes the way the linkage format for dylibs is calculated in a way that is necessary for linking against dylibs that statically link libstd.

[tamird]

Nice, that does fix it. Seems like we should update the unstable book. Should I send a PR?

[bjorn3]

Sure