build: improve python check for Windows

[compnerd]

Summary

If we have a new enough CMake, use find_package(Python3). This version is able to check both 32-bit and 64-bit versions and will setup everything properly without the user needing to specify PYTHON_HOME. This enables building lldb's python bindings on Windows under Azure's CI again.

[JDevlieghere]

I proposed this in https://reviews.llvm.org/D64881 and the consensus was that we didn't want to do this.

Also I don't think this should be a Windows-only thing.

[compnerd]

The reason for bringing this back up as a Windows specific thing is that currently, there is no good way to build LLDB with python support without having to specify additional details on *just* windows because the windows path is doing something special. This is trying to bring the windows path to parity with the Linux path.

[labath]

Yeah, I'd still like to avoid having multiple paths for configuring python, as one of them is bound to end up broken sooner or later. However, given that there's already talk about bumping the minimum cmake version, maybe we could do an lldb-specific bump first?

Though I am generally against aggressive version bumps, this python+windows situation is sufficiently messy that I think the bump may be worth it. Given that this code is python3 specific and other platforms still support python2, maybe we can make this bump windows-specific at first, and then extend it to other platforms once we officially stop supporting python2 ?

[+ other windows stakeholders: @amccarth, @ted, @aleksandr.urakov ]

lldb/cmake/modules/LLDBConfig.cmake

225

What if I use a single-config generator and build a release configuration. Is the "development" thingy still required?

[compnerd]

Yeah, doing an incremental rollout makes sense.

lldb/cmake/modules/LLDBConfig.cmake

225

Yes, it is - the component is the headers for building.

[amccarth]

In D69535#1724797, @labath wrote:

.. Given that this code is python3 specific and other platforms still support python2, maybe we can make this bump windows-specific at first, and then extend it to other platforms once we officially stop supporting python2 ?

Yes, please. It's a mess on Windows, so I'll support a Windows-specific version bump.

[compnerd]

Use @labath's suggestion of bumping minimum required version for Windows

[labath]

This looks fine to me, and it's really great to get rid of the that code, but it would be good for some some "windows person" to ack this too. I'm particularly interested in Stella's opinion, as according to http://lab.llvm.org:8011/buildslaves/win-py3-buildbot, her bot still runs cmake 3.11. @stella.stamenova, would it be possible to upgrade that bot to cmake>=3.13 ?

[compnerd]

@stella.stamenova ping

[stella.stamenova]

Sorry, I was out on vacation until today :).

The bot is actually running 3.14 already, I updated the host file to reflect that.

[compnerd]

GIT 2046d72e916

lldb/cmake/modules/LLDBConfig.cmake

function(find_python_libs_windows)
 
   message(STATUS "LLDB Found PythonExecutable: ${PYTHON_EXECUTABLE} (${PYTHON_VERSION_STRING})")
   message(STATUS "LLDB Found PythonLibs: ${PYTHON_LIB} (${PYTHONLIBS_VERSION_STRING})")
   message(STATUS "LLDB Found PythonDLL: ${PYTHON_DLL}")
   message(STATUS "LLDB Found PythonIncludeDirs: ${PYTHON_INCLUDE_DIR}")
 endfunction(find_python_libs_windows)
 
 if (NOT LLDB_DISABLE_PYTHON)
+  if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.13 AND CMAKE_SYSTEM_NAME STREQUAL Windows)
+    find_package(Python3 COMPONENTS Interpreter Development REQUIRED)
+    if(Python3_VERSION VERSION_LESS 3.5)
+      message(FATAL_ERROR "Python 3.5 or newer is required (found: ${Python3_VERSION})")
+    endif()
+    set(PYTHON_LIBRARY ${Python3_LIBRARIES})
+    include_directories(${Python3_INCLUDE_DIRS})
+  else()
     if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Windows")
       find_python_libs_windows()
 
       if (NOT LLDB_RELOCATABLE_PYTHON)
         file(TO_CMAKE_PATH "${PYTHON_HOME}" LLDB_PYTHON_HOME)
         add_definitions( -DLLDB_PYTHON_HOME="${LLDB_PYTHON_HOME}" )
       endif()
     else()
       find_package(PythonInterp REQUIRED)
       find_package(PythonLibs REQUIRED)
     endif()
 
     if (NOT CMAKE_CROSSCOMPILING)
       string(REPLACE "." ";" pythonlibs_version_list ${PYTHONLIBS_VERSION_STRING})
       list(GET pythonlibs_version_list 0 pythonlibs_major)
       list(GET pythonlibs_version_list 1 pythonlibs_minor)
 
       # Ignore the patch version. Some versions of macOS report a different patch
       # version for the system provided interpreter and libraries.
       if (NOT PYTHON_VERSION_MAJOR VERSION_EQUAL pythonlibs_major OR
           NOT PYTHON_VERSION_MINOR VERSION_EQUAL pythonlibs_minor)
         message(FATAL_ERROR "Found incompatible Python interpreter (${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR})"
                             " and Python libraries (${pythonlibs_major}.${pythonlibs_minor})")
       endif()
     endif()
 
     if (PYTHON_INCLUDE_DIR)
       include_directories(${PYTHON_INCLUDE_DIR})
     endif()
   endif()
+endif()
 
 if (LLDB_DISABLE_PYTHON)
   unset(PYTHON_INCLUDE_DIR)
   unset(PYTHON_LIBRARY)
   unset(PYTHON_EXECUTABLE)
   add_definitions( -DLLDB_DISABLE_PYTHON )
 endif()