vcpkg usd in debug mode: python linking error

[ju-manns]

Hi,
I am trying to build USD using version 25.2 of the usd vcpkg port on Windows.
I modified the portfile to enable python support using the vcpkg python. If I build in release mode only, all compiles fine. In debug mode however, I get the error

FAILED: pxr/external/boost/python/usd_python.dll pxr/external/boost/python/usd_python.lib
LINK : fatal error LNK1104: Cannot open file "python311.lib"

If I also pass -DPXR_USE_DEBUG_PYTHON:BOOL=ON in the portfile, I get LINK : fatal error LNK1104: Cannot open file "python311_d.lib" instead.
The linking command shows that the build system tries to link vcpkg_installed\x64-windows\lib\python3.lib.
However, when I remove the lines

OpenUSD/pxr/external/boost/python/CMakeLists.txt

Line 16 in 47117bc

${PYTHON_LIBRARIES}

I notice that the build system no longer tries to link vcpkg_installed\x64-windows\lib\python3.lib but the afforementioned error still shows up. Is there some duplicate linking of the python lib going on?

[meshula]

To the best of my knowledge vcpkg itself doesn't provide a debug build of python. Because msvc links to different runtimes for debug and release, I don't think you can accomplish a vcpkg based debug build without actually providing the python debug linked library yourself and setting up vcpkg to point to it, and that extends to any dependencies of python that might be supplied otherwise by vcpkg.

If someone else knows otherwise please let us know. What I wrote here is what I encountered when I attempted it. Unfortunately I don't have the recipe I used because I stopped when I realized dependencies like pyside would also need to be compiled for debug.

[jesschimein]

Filed as internal issue #USD-10678

(This is an automated message. See here for more information.)

[ju-manns]

To the best of my knowledge vcpkg itself doesn't provide a debug build of python. Because msvc links to different runtimes for debug and release, I don't think you can accomplish a vcpkg based debug build without actually providing the python debug linked library yourself and setting up vcpkg to point to it, and that extends to any dependencies of python that might be supplied otherwise by vcpkg.

If someone else knows otherwise please let us know. What I wrote here is what I encountered when I attempted it. Unfortunately I don't have the recipe I used because I stopped when I realized dependencies like pyside would also need to be compiled for debug.

vcpkg does provide python debug builds and we have a working usd vcpkg debug build linked against vcpkg's python. This error only occurs now that we want to update to 25.02 and use the new internal boost-python. The linking error also only occurs for this new module.

[meshula]

Thanks for the note. For my own knowledge, since I can't find details via google (the information I reported above is what I have in my notes) how do you instruct vcpkg to use a debug python?

[ju-manns]

The issue seems to be related to microsoft/vcpkg#33724 which is the reason, why there is a python_d lib on windows but no python_d.exe.
However, boost_python manages to link python_d.dll on Windows despite this issue in the python port. That's why we used to have a working debug usd build linked against python on Windows.
Therefor I think this issue is indeed a problem with how the new external/boost/python module tries to link python.

[meshula]

Ok, I worked through the cmake script, and here's what I found.

If you set PXR_USE_INTERNAL_BOOST_PYTHON to zero, then the linked library is specified in CMake via ${Boost_PYTHON_LIBRARY}. working through cmake/defaults/Packages.cmake we see we need to set these variables PXR_ENABLE_PYTHON_SUPPORT AND PXR_USE_BOOST_PYTHON , and then the following clause starting with if(PXR_ENABLE_PYTHON_SUPPORT) goes on to set up the python libraries and boost library variables, and then finally we find this

    if(PXR_USE_BOOST_PYTHON)
        if(WIN32 AND PXR_USE_DEBUG_PYTHON)
            set(Boost_USE_DEBUG_PYTHON ON)
        endif()

followed by another find_package. I have to guess that the answer to your question in or near one of these code blocks, and perhaps stepping through it with a python debugger might help determine why your debug libraries are not being found.

I don't have a way right now to try to do a windows debug python build, and the windows debug python build is not set up to run in the CI suite, so although I'm not able to dig deeper, I'm hopeful that maybe these clues are useful. If you are able to determine if the logic I'm pointing to here isn't working in your case (I am thinking that this is where the problem lies), that could point to a change we need to make in the detection logic.