[CMake] Object libraries and relative paths in Ninja

[Daniel Eiband]

Hi,

For a simple test I've got the following directory structure:

|- build
|- project
|  |- CMakeLists.txt
|  |- Main.cpp
|- CMakeLists.txt
|- Test.cpp

project/CMakeLists.txt has the following content:

  cmake_minimum_required(VERSION 3.12)

  project(Reproducer LANGUAGES CXX)

  add_subdirectory("${CMAKE_CURRENT_SOURCE_DIR}/.." "${CMAKE_CURRENT_BINARY_DIR}/..")

  add_executable(Reproducer)
  target_sources(Reproducer PRIVATE Main.cpp)
  target_link_libraries(Reproducer PRIVATE ReproducerLibrary)


And CMakeLists.txt has the following content:

  add_library(ReproducerLibrary OBJECT)
  target_sources(ReproducerLibrary PRIVATE Test.cpp)


When I now run the commands:

cd build
cmake.exe -G Ninja ..\..\project
cmake.exe --build .

Then I get the error:

ninja: error: '<absolute-path>/ReproducerLibrary.dir/Test.cpp.obj', needed by 'Reproducer.exe', missing and no known rule to make it

I noticed, that the build.ninja the build rule for Test.cpp.obj has a relative path, whereas the link dependency to Test.cpp.obj is an absolute path.

Is this a known issue?

Regards,
Daniel
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