pkg-config file is broken when CMAKE_INSTALL_{INCLUDE,LIB}DIR is absolute

[alexshpilkin]

As per title: CMakeLists.txt has

  set(prefix ${CMAKE_INSTALL_PREFIX})
  set(exec_prefix "\$\{prefix\}")
  set(libdir "\$\{prefix\}/${CMAKE_INSTALL_LIBDIR}")
  set(includedir "\$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")

and so can’t handle absolute paths in CMAKE_INSTALL_{INCLUDE,LIB}DIR. This leads to a broken .pc file on NixOS in particular.

Identical to Matroska-Org/libmatroska#62. Similar to open-source-parsers/jsoncpp#1199. See “Concatenating paths when building pkg-config files” for a discussion of the problem in a somewhat different context and a suggested fix (I don’t know CMake myself, sorry).

[robUx4]

I tried using cmake_path but cmake being cmake it doesn't work for obscure reasons

  if(${CMAKE_VERSION} VERSION_LESS "3.20.0") 
    set(libdir "\$\{prefix\}/${CMAKE_INSTALL_LIBDIR}")
    set(includedir "\$\{prefix\}/${CMAKE_INSTALL_INCLUDEDIR}")
  else()
    cmake_path(RELATIVE_PATH "${CMAKE_INSTALL_LIBDIR}" BASE_DIRECTORY "${CMAKE_INSTALL_PREFIX}" libdir)
    cmake_path(RELATIVE_PATH ${CMAKE_INSTALL_INCLUDEDIR} BASE_DIRECTORY ${CMAKE_INSTALL_PREFIX} includedir)
  endif()

[build] CMake Error at CMakeLists.txt:135 (cmake_path):
[build]   cmake_path RELATIVE_PATH called with unexpected arguments.
[build] 
[build] 
[build] CMake Error at CMakeLists.txt:136 (cmake_path):
[build]   cmake_path RELATIVE_PATH called with unexpected arguments.
[build] 
[build] 

[robUx4]

Apparently it wants variables not paths. Luckily it's already in a variable...