windeployqt doesn't deploy qwindowsd.dll for a debug application - c++

Question

I'm trying to use windeployqt.exe (Qt 5.13.2) to deploy dlls for a debug application generated by CMake 3.16. All the dlls are deployed correctly except for the platform plugin dll, which deploys qwindows.dll instead of qwindowsd.dll and results in the following error when I try to run the executable:
This application failed to start because no Qt platform plugin could be initialized.
So far, I've tried:
Specifying --debug on the windeployqt command line. That failed because Qt5Coredd.dll could not be found (note the double d's).
Verifying that no Qt plugin related environment variables are set.
Checked PATH to make sure it doesn't contain any folder with a platforms directory.
If I copy qwindowsd.dll manually, everything works fine. However I'd really like to figure out what I'm doing wrong with windeployqt.

Answer 1

This is apparently a known problem that Qt have dragged their heels on fixing, but I figured out a workaround in CMake - this works for both the Ninja generator/Visual Studio's built in CMake support as well as the regular Visual Studio solution generator
# Split windeployqt into 2 parts to fix issue with deploying debug plugins
add_custom_command(TARGET MyApp POST_BUILD
COMMAND ${QT_PATH}/bin/windeployqt --compiler-runtime --no-plugins ${MY_APP_EXE})
if (CMAKE_GENERATOR STREQUAL "Ninja")
# Ninja is a single-config generator so we can use CMAKE_BUILD_TYPE to generate different commands
if (CMAKE_BUILD_TYPE STREQUAL "Debug")
add_custom_command(TARGET MyApp POST_BUILD
COMMAND ${QT_PATH}/bin/windeployqt --debug --no-compiler-runtime --no-translations --no-libraries ${MY_APP_EXE})
else()
add_custom_command(TARGET MyApp POST_BUILD
COMMAND ${QT_PATH}/bin/windeployqt --release --no-compiler-runtime --no-translations --no-libraries ${MY_APP_EXE})
endif()
else()
# if in MSVC we have to check the configuration at runtime instead of generating different commands
add_custom_command(TARGET MyApp POST_BUILD
COMMAND cmd.exe /c if "$(Configuration)" == "Debug" ${QT_PATH}/bin/windeployqt --debug --no-compiler-runtime --no-translations --no-libraries ${MY_APP_EXE})
add_custom_command(TARGET MyApp POST_BUILD
COMMAND cmd.exe /c if not "$(Configuration)" == "Debug" ${QT_PATH}/bin/windeployqt --release --no-compiler-runtime --no-translations --no-libraries ${MY_APP_EXE})
endif()