[Question] How can I find_package from dependent crate?

[lemoncmd]

I have two crates with cmake, and one crate A depends on another crate B.

How can a cmake project in crate A find_package from a cmake project in crate B?

crate A -> cmake project A
| [dependencies]    | find_package?
v                   v
crate B -> cmake project B

[sksat]

The actual crate source directory is managed by Cargo, so we can't know where it is. Unless you explicitly specify a path, it will reside deep in a directory such as ~/.cargo/regostry/ or ~/.cargo/git. And there is no official way to know the actual location of dependencies from build script.

There are two workarounds for this problem.

1. Propagate CARGO_MANIFEST_DIR using links manifest key
   In the build script, the actual location of self crate source directory can be obtained using CARGO_MANIFEST_DIR.
   We can use The links Manifest Key to propagate the directory to the upper crate.
   However, links is designed for -sys crate etc. and has some limitations.

2. Use cargo-metadata
   cargo-metadata(1) can be used to retrieve various metadata, including the actual location of the source directory.
   ex: dirname $(cargo metadata --format-version 1 | jq '.packages[] | select(.name == "B")' | .manifest_path)
   For use from within the build script, the cargo_metadata crate will be useful.

[tgross35]

Thanks @sksat for the great answer. I don't think there is anything specific to cmake-rs here, so I'll move this to a discussion.