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FindBoost: Improve compiler prefix detection for GCC 5+ and clang 4+

Mateusz Łoskot requested to merge mloskot/cmake:ml/FindBoost-compiler-guess-update into master

FindBoost: Improve compiler prefix detection for GCC 5+ and clang 4+

Add recognition of compiler version and prefix for clang.

Accommodate changes to version numbering scheme for GCC 5+ and clang 4+

  • Minor number becomes patch, so excluded it from compiler prefix.
  • Improves searching for Boost 1.69+ libraries built with GCC 5+ and clang 4+, where library names are generated with compiler tag based on major version only eg. -gcc5 for GC 5.5.0 or -clang6 for clang 6.0.0
  • Follows up related changes in upcoming Boost 1.69 https://github.com/boostorg/build/pull/349

Dump detected compiler version in Boost_DEBUG message.

Replace use of CMAKE_COMPILER_IS_GNUCXX with CMAKE_CXX_COMPILER_ID.

Problem Example

Let's consider building Boost 1.69+ (current master or later) with GCC 5.5.0 and clang 6.0.0 on Linux:

b2 toolset=gcc   variant=debug,release address-model=64 --layout=versioned --with-system stage
b2 toolset=clang variant=debug,release address-model=64 --layout=versioned --with-system stage

This will generate the following libraries:

$ ls -1 libboost_system*
libboost_system-clang6-mt-d-x64-1_69.a
libboost_system-clang6-mt-d-x64-1_69.so
libboost_system-clang6-mt-d-x64-1_69.so.1.69.0
libboost_system-clang6-mt-x64-1_69.a
libboost_system-clang6-mt-x64-1_69.so
libboost_system-clang6-mt-x64-1_69.so.1.69.0
libboost_system-gcc5-mt-d-x64-1_69.a
libboost_system-gcc5-mt-d-x64-1_69.so
libboost_system-gcc5-mt-d-x64-1_69.so.1.69.0
libboost_system-gcc5-mt-x64-1_69.a
libboost_system-gcc5-mt-x64-1_69.so
libboost_system-gcc5-mt-x64-1_69.so.1.69.0

Now, we run CMake for a project that find_package for Boost:

cmake -DBOOST_ROOT=/mnt/d/boost.wsl -DBoost_ARCHITECTURE=-x64 ..

This will fail because Boost_COMPILER is guessed as -gcc55.

Obvious but inconvenient workaround is to fix the compiler tag manually:

cmake -DBOOST_ROOT=/mnt/d/boost.wsl -DBoost_ARCHITECTURE=-x64 -DBoost_COMPILER=-gcc5 ..

The changes propose in this MR improve the lookup and free users from manually specifying the compiler tag.

Topic-rename: FindBoost-compiler-guess-update

Edited by Mateusz Łoskot

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