CMP0089

Compiler id for IBM Clang-based XL compilers is now XLClang.

CMake 3.15 and above recognize that IBM’s Clang-based XL compilers that define __ibmxl__ are a new front-end distinct from xlc with a different command line and set of capabilities. CMake now prefers to present this to projects by setting the CMAKE_<LANG>_COMPILER_ID variable to XLClang instead of XL. However, existing projects may assume the compiler id for Clang-based XL is just XL as it was in CMake versions prior to 3.15. Therefore this policy determines for Clang-based XL compilers which compiler id to report in the CMAKE_<LANG>_COMPILER_ID variable after language <LANG> is enabled by the project() or enable_language() command. The policy must be set prior to the invocation of either command.

The OLD behavior for this policy is to use compiler id XL. The NEW behavior for this policy is to use compiler id XLClang.

This policy was introduced in CMake version 3.15. Use the cmake_policy() command to set this policy to OLD or NEW explicitly. Unlike most policies, CMake version 3.19.0-rc3 does not warn by default when this policy is not set and simply uses OLD behavior. See documentation of the CMAKE_POLICY_WARNING_CMP0089 variable to control the warning.