Ports fail on Windows since Python update

[cskrisz]

Since Python was updated from 3.5.4 to 3.7.3 (#6383) importing external modules does not work in scripts, e.g.:

-- Found PythonInterp: F:/vcpkg/downloads/tools/python/python3/python.exe (found version "3.7.3") 
-- Constructing LLVMBuild project information
CMake Error at CMakeLists.txt:683 (message):
  Unexpected failure executing llvm-build: Traceback (most recent call last):

    File "F:/vcpkg/buildtrees/llvm/src/llvm-7.0.0.src/utils/llvm-build/llvm-build", line 3, in <module>
      import llvmbuild

  ModuleNotFoundError: No module named 'llvmbuild'

This behavior is unique to the Python embeddable package and it seems to work that way since Python version 3.6.0.

The build works fine when

• Using the host's Python installation or
• Adding the module path to vcpkg\downloads\tools\python\python3\python37._pth

Packages that use Python 3 and might be affected: botan, clblas, ctemplate, folly, gl3w, glad, gtk, hyperscan, hyperscan, llvm, open62541, opencl, physx, pybind11, qscintilla, qt5-base, shaderc, shogun, spirv-tools, xmsh

Related issues: #6979, #6984, #7066

Machine setup: Windows 10 1903 x64, VS2019

[MVoz]

most likely there is not enough module to build
example of use

https://github.com/microsoft/vcpkg/blob/master/ports/duktape/portfile.cmake
https://github.com/microsoft/vcpkg/blob/master/ports/open62541/portfile.cmake

vcpkg_find_acquire_program(PYTHON3)
get_filename_component(PYTHON3_DIR "${PYTHON3}" DIRECTORY)
vcpkg_add_to_path("${PYTHON3_DIR}")
if(NOT EXISTS ${PYTHON3_DIR}/easy_install${EXECUTABLE_SUFFIX})
    if(NOT EXISTS ${PYTHON3_DIR}/Scripts/pip${EXECUTABLE_SUFFIX})
        vcpkg_download_distfile(GET_PIP
            URLS "https://bootstrap.pypa.io/get-pip.py"
            FILENAME "tools/python/python3/get-pip.py"
            SHA512 99520d223819708b8f6e4b839d1fa215e4e8adc7fcd0db6c25a0399cf2fa10034b35673cf450609303646d12497f301ef53b7e7cc65c78e7bce4af0c673555ad
        )
        execute_process(COMMAND ${PYTHON3_DIR}/python${EXECUTABLE_SUFFIX} ${PYTHON3_DIR}/get-pip.py)
    endif()
    execute_process(COMMAND ${PYTHON3_DIR}/Scripts/pip${EXECUTABLE_SUFFIX} install six)
else()
    execute_process(COMMAND ${PYTHON3_DIR}/easy_install${EXECUTABLE_SUFFIX} six)
endif()

pip install six)

or manual

F:/vcpkg/downloads/tools/python/python3/python.exe -mpip install -U --force six

although the file python37._pth
can also be the cause, it can be simply removed

[cskrisz]

Primarily, the problem is with modules located in the same folder as the script being run. (Though pip packages are likely affected as well.)

[wasabinza]

Removing the vcpkg\downloads\tools\python\python3\python37._pth file appeared to be sufficient for me to build llvm with vcpkg.