Add a Post-Build Event on Windows to copy the correct custom Python DLL to the LLDB binaries dir

[enlight]

Summary

After a developer builds LLDB from source on Windows (assuming they've built it with Python support enabled), they may be somewhat flustered when it fails to launch with a cryptic error.

This happens because Windows can't find python27.dll (or python27_d.dll in case LLDB was built in debug mode). Many developers may have previously installed a release build of Python 2.7 and will not notice anything is amiss when they run a release build of LLDB because Windows will load the python27.dll from one of the system directories or PATH (rather than the one that the LLDB build instructions tell them to build). The issue tends to be more pronounced with debug builds of LLDB, since fewer developers probably have python27_d.dll sitting in one of the Windows system directories.

To ensure Windows loads the correct custom built Python DLL when launching LLDB I've added a post-build event that copies the relevant DLL (based on the LLDB build configuration) from PYTHON_HOME to the directory in which the LLDB executable is generated.

[zturner]

This looks great. This has always really annoyed me. One thing I want to point out based on your summary of the patch. A user *must* build Python himself, even if he is building a release version of LLDB. You *cannot* use the version that is installed on the system. The reason is because the release python on python.org is compiled with VC 2008, and LLDB is compiled with VC 2013. The two CRTs are ABI incompatible so you'll get heap corruption and other strange errors if you don't build Python yourself.

Patch looks fine though

lldb/trunk/CMakeLists.txt

add_custom_target( finish_swig ALL
         COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/finishSwigWrapperClasses.py "--srcRoot=${LLDB_SOURCE_DIR}" "--targetDir=${CMAKE_CURRENT_BINARY_DIR}/scripts" "--cfgBldDir=${CMAKE_CURRENT_BINARY_DIR}/scripts" "--prefix=${CMAKE_BINARY_DIR}" "--cmakeBuildConfiguration=${CMAKE_CFG_INTDIR}" -m
         DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/scripts/finishSwigWrapperClasses.py
         COMMENT "Python script sym-linking LLDB Python API")
     # We depend on liblldb being built before we can do this step.
     add_dependencies(finish_swig liblldb argdumper)
 
     # Ensure we do the python post-build step when building lldb.
     add_dependencies(lldb finish_swig)
+
+    # Add a Post-Build Event to copy the custom Python DLL to the lldb binaries dir so that Windows can find it when launching
+    # lldb.exe or any other executables that were linked with liblldb.
+    if (WIN32 AND NOT "${PYTHON_DLL}" STREQUAL "")
+        # When using the Visual Studio CMake generator the lldb binaries end up in Release/bin, Debug/bin etc.
+        file(TO_NATIVE_PATH "${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin" LLDB_BIN_DIR)
+        file(TO_NATIVE_PATH "${PYTHON_DLL}" PYTHON_DLL_NATIVE_PATH)
+        add_custom_command(
+            TARGET finish_swig
+            POST_BUILD
+            COMMAND "${CMAKE_COMMAND}" -E copy ${PYTHON_DLL_NATIVE_PATH} ${LLDB_BIN_DIR}
+            COMMENT "Copying Python DLL to LLDB binaries directory.")
+    endif ()
 endif ()