Linking against multiple static libraries that use cxx

[jbruechert]

In my C++ project I have two rust crates that export a C++ API using cxx.

That setup ends in a bunch of linking errors like this:

/usr/bin/ld: libangelfish_readability.a(cxx-546393ec83734d88.cxx.77528ncj-cgu.12.rcgu.o): in function `cxxbridge1$exception':
/home/jbb/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/cxx-1.0.49/src/symbols/exception.rs:6: multiple definition of `cxxbridge1$exception'; libangelfish_adblock.a(cxx-506fb85a29953a06.cxx.6ziszbha-cgu.12.rcgu.o):/home/jbb/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/cxx-1.0.49/src/symbols/exception.rs:6: first defined here
/usr/bin/ld: libangelfish_readability.a(cxx-546393ec83734d88.cxx.77528ncj-cgu.12.rcgu.o): in function `cxxbridge1$str$from':
/home/jbb/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/cxx-1.0.49/src/symbols/rust_str.rs:18: multiple definition of `cxxbridge1$str$from'; libangelfish_adblock.a(cxx-506fb85a29953a06.cxx.6ziszbha-cgu.12.rcgu.o):/home/jbb/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/cxx-1.0.49/src/symbols/rust_str.rs:18: first defined here

Can I do anything about it apart from moving everything into one crate, or is this a general limitation?

[Geobert]

What's the status on this? Any clue if it's a limitation or if some method is available to make that work?

[dtolnay]

According to https://cxx.rs/build/other.html (source: @adetaylor in #345):

you first need to use rustc and/or cargo to generate a single Rust staticlib target and pass that into your foreign linker invocation.

• If you need to link multiple Rust subsystems, you will need to generate a single staticlib perhaps using lots of extern crate statements to include multiple Rust rlibs. Multiple Rust staticlib files are likely to conflict.

That all seems consistent with what you've described. Rust does not expose any way for a C++ linker to link multiple Rust staticlibs. That part always has to be done by Rust's linker.

rust-lang/rust#73632 has more extensive discussion of this situation.