CMAKE_SHARED_LIBRARY_SUFFIX in script processing (-P) mode

Code
1

When I use cmake in -P mode (i.e. executing a script .cmake file) the standard CMake variable for shared library suffixes doesn’t seem to be defined:

~ $ more libsuffix.cmake 
message("CMAKE_SHARED_LIBRARY_SUFFIX: ${CMAKE_SHARED_LIBRARY_SUFFIX}")
~ $ cmake -P libsuffix.cmake 
CMAKE_SHARED_LIBRARY_SUFFIX:

It seems to work fine in normal usage - the variable is undefined only in -P mode. Can anyone advise on the correct way to access this definition in -P mode?

2

I suspect this is one of the variables set during platform checks the project() command does, so it just cannot be available in script mode.

3

Do different build tools use different conventions for this? I thought it was operating system specific, and if so couldn’t that be built in knowledge?

4

These variables are set by the specific CMake script under ${CMAKE_ROOT}/Modules/Platform

This is undocumented, but this script does work to define CMAKE_SHARED_LIBRARY_SUFFIX

get_property(cmake_role GLOBAL PROPERTY CMAKE_ROLE)
if(cmake_role STREQUAL "SCRIPT")
  set(CMAKE_PLATFORM_INFO_DIR ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY})
  # define CMAKE_HOST*, CMAKE_SYSTEM*, etc.
  include(${CMAKE_ROOT}/Modules/CMakeDetermineSystem.cmake)
  # set booleans like CYGWIN
  include(${CMAKE_ROOT}/Modules/CMakeSystemSpecificInitialize.cmake)

  include(${CMAKE_ROOT}/Modules/CMakeSystemSpecificInformation.cmake)

  include(${CMAKE_ROOT}/Modules/Platform/${CMAKE_SYSTEM_NAME}.cmake)
endif()

include(${CMAKE_ROOT}/Modules/CMakePrintSystemInformation.cmake)

run that in cmake -P and it works

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