cannot use CMAKE_SOURCE_DIR in toolchain file

Code
1

When trying to include something from CMAKE_SOURCE_DIR in a toolchain-file, cmake seems to make a flat copy of the file for compiler-tests, then /CMakeFiles/CMakeTmp/CMakeLists.txt:3 cannot find the include-file in /CMakeFiles/CMakeTmp/

Example: we are using conan and our compiler is provided as a conan-package. Conan will generate a conanbuildinfo.cmake which will provide path-variables for all tools. toolchain-file:

```
include(${CMAKE_SOURCE_DIR}/conanbuildinfo.cmake)
set(CMAKE_C_COMPILER ${CONAN_BIN_DIRS_CLANG}/clang-cl.exe)
set(CMAKE_CXX_COMPILER ${CONAN_BIN_DIRS_CLANG}/clang-cl.exe)
set(CMAKE_LINKER ${CONAN_BIN_DIRS_CLANG}/lld-link.exe)
```

output:

```
-- The C compiler identification is Clang 9.0.0 with MSVC-like command-line
-- The CXX compiler identification is Clang 9.0.0 with MSVC-like command-line
-- Check for working C compiler: user/.conan/data/clang/9.0.0/tools/stable/package/9d74748ca8155c54bee5ded2267de5f3e409cf81/bin/clang-cl.exe
CMake Error at C:/src/Example/tool-clang-windows-x86.cmake:8 (include):
  include could not find load file:

    C:/src/Example/CMakeFiles/CMakeTmp/conanbuildinfo.cmake
Call Stack (most recent call first):
  C:/src/Example/CMakeFiles/3.15.4/CMakeSystem.cmake:6 (include)
  C:/src/Example/CMakeFiles/CMakeTmp/CMakeLists.txt:3 (project)
```
2

The toolchain file is C:/src/Example/tool-clang-windows-x86.cmake, but where is conanbuildinfo.cmake exactly? If it is a sibling of the toolchain file, then I would use

include("${CMAKE_CURRENT_LIST_DIR}/conanbuildinfo.cmake")
3

Sorry for reviving an old topic, but I think it makes sense.

I have the same issue, only in my case the included file is not a sibling but a few directories above - meaning I can’t use CMAKE_CURRENT_LIST_DIR as starting point. I’d really want to specify it from CMAKE_SOURCE_DIR instead.
Is this possible? If not, why not?

Edit: I can do something like ${CMAKE_CURRENT_LIST_DIR}../../../myfile.cmake so I guess the question “why” I can’t base this off off CMAKE_SOURCE_DIR still stands?

1 Like
4

Toolchain files are used not just for the main project, but also for try_compile() calls which create their own separate mini-projects to implement the compile test. For these separate mini-projects, the CMAKE_SOURCE_DIR would be a different directory to the value reported by the main project’s CMAKE_SOURCE_DIR. You should consider the only reliable variables to be those that are relative to the location of the toolchain file itself (e.g. CMAKE_CURRENT_LIST_DIR).

2 Likes
5

Thank you. Very helpful.
Is there a link about CMake variables and their initialization readiness?

6

That’s a pretty specific topic. The problem isn’t to do with initialization though, it’s about the context in which code executes. People don’t tend to think about (perhaps aren’t aware of) the different contexts in which a toolchain file might be used. The best way to shield yourself from that is to make your toolchain files completely independent of the project they are used with. If your toolchain file is tied to the project, that’s a bit of a warning that something probably isn’t quite right.