Unclear what Config::build() returns

[ExpHP]

The output of this function is confusing and undocumented.

Based on the code samples in ~~README.md~~ lib.rs, it would appear to be the directory where libs were installed. However, printing its value, I see that it is simply the install prefix (target/debug/build/lammps-sys-96aab2de8377bb22/out), and I need to instead write something like

let dir = cmake.build();
// I don't even know if this is portable...
println!("cargo:rustc-link-search=native={}", dir.join("lib64").display());

I'm not sure what to make of this. I'd call it a bug, but that's assuming that the function is supposed to return the libs dir!

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Note: To reproduce what I'm seeing, this isn't exactly minimal, but:

git clone https://github.com/ExpHP/lammps-sys
cd lammps-sys
git checkout 01c3d3bff
git submodule init
git submodule update
cargo build -v

and watch the build script output or linker flags. You'll see the path target/debug/build/lammps-sys-xxxxxxxxx/out/lib64, generated by this line of code, indicating that the return value ended in out as opposed to out/lib or out/lib64.

I see this even on the travis docker image, where much to my chagrin, it actually installs them to lib/. (of course, the linking step fails there!)

[alexcrichton]

Right now I believe it's the root of the installation directory, but a PR to improve the docs would be much appreciated!

[ExpHP]

Hmm. I was about to ask if this means that the code examples in lib.rs are incorrect—but then I noticed that there is also a build free function, whose output is documented:

/// Builds the native library rooted at `path` with the default cmake options.
/// This will return the directory in which the library was installed.

Maybe I've actually run into a bug, and the function is supposed to return [OUT_DIR]/lib64 in my case? Or maybe it is supposed to return [OUT_DIR], and is also supposed to put the libraries there (but somehow isn't in this case)?

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Addendum: I decided to start surveying cmake's dependent crates, and the first one I checked has this which definitely seems to suggest that the examples are wrong and the free function's documentation is misleading!

[alexcrichton]

I believe returning$OUT_DIR is correct in that your crate will locally need to append lib64

[joelgallant]

I think this confusion comes from the library with the CMakeLists.txt

CMake doesn't, strictly speaking, always produce binaries in the same place. The default target that cmake-rs uses is install, but you probably want cmake.build_target('lammps').build() (doc)

lammps installs to CMAKE_INSTALL_LIBDIR as seen here