Due to the way the qt-cmake script injects its CMAKE_TOOLCHAIN_FILE argument into the cmake command line, the script is only usable to configure a CMake build system. It cannot be used to run subsequent commands like:

qt-cmake --build _builddir_
qt-cmake --install _builddir_

...because the -DCMAKE_TOOLCHAIN_FILE=... argument is not valid in those modes.

I brought this up with the CMake team, and they suggested using the CMAKE_TOOLCHAIN_FILE environment variable to set the toolchain file, rather than the -D argument, since the environment variable is safe in any mode. (It'll simply be ignored, during --build or --install runs.)

IOW,

# Instead of ending qt-cmake with...
exec "$cmake_path" -DCMAKE_TOOLCHAIN_FILE="$toolchain_path"  "$@"

# use...
CMAKE_TOOLCHAIN_FILE="$toolchain_path" exec "$cmake_path" "$@"

...and qt-cmake will become a complete cmake command alternative for Qt users.