Path remapping ICE from unnecessary_transmutes suggestion

[Wyvern]

thread 'rustc' panicked at compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs:92:65:
ok: SourceNotAvailable { filename: Real(Remapped { local_path: None, virtual_name: "index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.24/src/macros.rs" }) }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: please make sure that you have updated to the latest nightly

note: rustc 1.88.0-nightly (d7ea436a0 2025-04-24) running on x86_64-apple-darwin

note: compiler flags: --crate-type lib -C embed-bitcode=no -Z unstable-options -Z remap-path-scope=all -C prefer-dynamic -C debug-assertions=off -C overflow-checks=on -C rpath -C strip=debuginfo -Z unstable-options -C prefer-dynamic -C target-cpu=native -Z tune-cpu=native -Z binary-dep-depinfo -Z checksum-hash-algorithm=blake3

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_built] building MIR for `x86_64::sse2::<impl at index.crates.io-1949cf8c6b5b557f/ppv-lite86-0.2.21/src/x86_64/sse2.rs:887:1: 887:64>::to_scalars`
#1 [check_unsafety] unsafety-checking `x86_64::sse2::<impl at index.crates.io-1949cf8c6b5b557f/ppv-lite86-0.2.21/src/x86_64/sse2.rs:887:1: 887:64>::to_scalars`
... and 1 other queries... use `env RUST_BACKTRACE=1` to see the full query stack

thread 'rustc' panicked at compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs:92:65:
ok: SourceNotAvailable { filename: Real(Remapped { local_path: None, virtual_name: "index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.24/src/macros.rs" }) }

error: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: please make sure that you have updated to the latest nightly

note: rustc 1.88.0-nightly (d7ea436a0 2025-04-24) running on x86_64-apple-darwin

note: compiler flags: --crate-type lib -C embed-bitcode=no -Z unstable-options -Z remap-path-scope=all -C prefer-dynamic -C debug-assertions=off -C overflow-checks=on -C rpath -C strip=debuginfo -Z unstable-options -C prefer-dynamic -C target-cpu=native -Z tune-cpu=native -Z binary-dep-depinfo -Z checksum-hash-algorithm=blake3

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [mir_built] building MIR for `x86_64::sse2::avx2::<impl at index.crates.io-1949cf8c6b5b557f/ppv-lite86-0.2.21/src/x86_64/sse2.rs:1683:5: 1683:58>::to_scalars`
#1 [check_unsafety] unsafety-checking `x86_64::sse2::avx2::<impl at index.crates.io-1949cf8c6b5b557f/ppv-lite86-0.2.21/src/x86_64/sse2.rs:1683:5: 1683:58>::to_scalars`

[DaniPopes]

#136083 cc @bend-n

[bend-n]

wait whats the repro?

[jieyouxu]

@Wyvern can you provide a more self-contained / complete reproducer? It's hard to determine how to reproduce this ICE, since based on the backtrace we can only guess it involves zerocopy's macro + path remapping.

[jieyouxu]

Nvm I synthesized a repro based on zerocopy's src/macros.rs (not minimal because I couldn't be bothered further trimming it down). The macro can probably be trimmed down a lot.

// transmute.rs
#[macro_export]
macro_rules! transmute {
    ($e:expr) => {{
        let e = $e;
        if false {
            todo!()
        } else {
            let u = unsafe {
                #[allow(clippy::missing_transmute_annotations)]
                unsafe { std::mem::transmute(e) }
            };
            u
        }
    }}
}

// foo.rs
#![crate_type = "rlib"]

fn bytes_at_home(x: [u8; 4]) -> u32 {
    unsafe { transmute::transmute!(x) }
}

$ rustc +nightly -Zunstable-options -Z remap-path-scope=all transmute.rs --crate-type=rlib --remap-path-prefix=/home/=/x
$ rustc +nightly foo.rs --extern transmute=libtransmute.rlib

thread 'rustc' panicked at compiler/rustc_mir_transform/src/check_unnecessary_transmutes.rs:92:65:
ok: SourceNotAvailable { filename: Real(Remapped { local_path: None, virtual_name: "/x/joe/repos/transmute.rs" }) }
stack backtrace:
[...]