Map CMake compilers to cargo build environment variables

[Chaz6]

I tried to compile a project that failed because it used c++ instead of the compiler specified in CMAKE_CXX_COMPILER (for example, clang++). I temporarly fixed this by making a link to clang++ from c++ in a location searched by $PATH before /usr/bin, but I think the better solution would be for corrosion to use the compiler specified by CMAKE_CXX_COMPILER.

[AndrewGaspar]

Was this in the context of a build script in Cargo? This is something I've wanted to fix at some point - basically, when invoking cargo, set CC, CXX, etc. to the compilers selected by CMake.

[Chaz6]

The project I was trying to build is https://invent.kde.org/graphics/pikasso/ and I am afraid I am not a rust expert, but I enjoy experimenting with new things! I could not find a Cargo.toml but the CMakeLists.txt contains this:-

find_package(Corrosion)
set_package_properties(Corrosion PROPERTIES
    PURPOSE "Required for transforming the paths to vertices and indices"
    DESCRIPTION "CMake scripts to seamlessly build and link to targets using cargo"
    URL https://github.com/AndrewGaspar/corrosion
)

Edit: I did not look very hard. There is a Cargo.toml and it contains the following:-

[package]
name = "tessellation-ffi"
version = "0.1.0"
authors = ["Carl Schwan <carlschwan@kde.org>"]
edition = "2018"

[lib]
crate-type = ["staticlib"]
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[build-dependencies]
cxx-build = "1.0.28"

[dependencies]
lyon = {version = "0.17.0" }
cxx = "1.0"

[AndrewGaspar]

Yeah, looks like the case then - this is a known issue. Thank you for filing this!

As a work around, you should also be able to set CXX=clang++ and get the same behavior, I think.

[surprized]

Not sure what is going wrong here, but I packaged PIkasso without modiying anything, except I exported some rustc flags.
The current gcc bundled in Tumbleweed is gcc-10 IIRC.

[AndrewGaspar]

This issue only comes up if you're trying to use a compiler that is not your "default" system compiler (i.e. mapped to cc/c++, or set via the CC/CXX environment variables). What's happening is that CMake and the Cargo cc crate disagree on which C++ compiler to use because @Chaz6 explicitly set the C++ compiler to use via CMAKE_CXX_COMPILER.