Preface

This one is a bit of a doozy and I can't tell if it's a rustc issue or a cbindgen issue or both, so I'm going to cross-report them so both projects can be aware.

I don't have a minimal reproduction, but it is easily reproducible in my repo.

Repo: https://github.com/BVE-Reborn/bve-reborn
Working Commit: 52b3ec6
Failing Commit: 7799c04

The only difference is the addition of the crate type of cdylib. (rlib is there, but it reproduces on my next commit which removed it)

System Info

Xubuntu 18.04

Rust and Cargo locked to nightly-2020-01-16
rustc: rustc 1.42.0-nightly (3291ae339 2020-01-15)
cargo: cargo 1.42.0-nightly (ad3dbe10e 2020-01-13)

CBindgen latest, compiled on the same nightly toolchain:
cbindgen 0.12.2

Repro

The rustc command is the exact command cbindgen runs to get macro expanded data.

This all takes place in the root of my repo.

cargo build
cargo rustc --lib --manifest-path bve-native/Cargo.toml  -p "bve-native:0.0.0-Placeholder" "--verbose" -- -Z unstable-options --pretty=expanded 

Both succeed as expected. However if you call cbindgen it fails, and the rustc no longer outputs anything at all.

# Succeeds
cargo build

# Fails citing an issue with compiling
# Occasionally must be run twice
cbindgen bve-native/ -c bve-native/cbindgen.toml -v

# Returns zero, but outputs nothing.
cargo rustc --lib --manifest-path bve-native/Cargo.toml  -p "bve-native:0.0.0-Placeholder" "--verbose" -- -Z unstable-options --pretty=expanded 
# You can call ^ as many times as you want, it will always fail

The problem goes away when you cargo clean and reappears by running cbindgen again.

Comments

I have no idea what or who is causing this issue.

I feel like even if cbindgen is ultimately the "cause" of the bug, the expansion shouldn't be able to fail and not output anything without erroring (and returning != 0) in some way.

Notes:

Possibly relevant cbindgen code: https://github.com/eqrion/cbindgen/blob/master/src/bindgen/cargo/cargo_expand.rs#L129
rustc issue: rust-lang/rust#68333

Thanks!