find_package interferes with existing installation

[LecrisUT]

This is a quick but rather subtle issue. My CMake list file goes like:

if (NOT TARGET Spglib::symspg)
    find_package(Spglib CONFIG)
    if (NOT Spglib_FOUND)
        message(STATUS "Using bundled spglib sources")
        add_subdirectory(${PROJECT_SOURCE_DIR}/.. _deps/spglib-build)
    endif ()
endif ()

If I pip install from scratch it works just fine, i.e. the add_subdirectory is used. But if I run pip install again, then it picks up the current installation and it goes through find_package even though it is later removed at the install stage when the previous version is uninstalled.

I think the issue is with working around NO_CMAKE_INSTALL_PREFIX, but it is weird, shouldn't that point to tmp folder that would not interfere? Otherwise I did not configure any prefix for it to use. Any clues on what's happening here and how to work around it?

I believe the issue is with:

scikit-build-core/src/scikit_build_core/builder/builder.py

Lines 133 to 139 in 4f06e8c

	# Add site-packages to the prefix path for CMake
	site_packages = Path(sysconfig.get_path("purelib"))
	self.config.prefix_dirs.append(site_packages)
	logger.debug("SITE_PACKAGES: {}", site_packages)
	if site_packages != DIR.parent.parent:
	self.config.prefix_dirs.append(DIR.parent.parent)
	logger.debug("Extra SITE_PACKAGES: {}", site_packages)

[henryiii]

I'm assuming you haven't set CMAKE_EXPORT_PACKAGE_REGISTRY, which could muddle with this.

The CMake way to do this is with the new-ish (3.24 IIRC) FindPackage + FetchContent integration:
(see https://github.com/scikit-hep/boost-histogram/blob/8ded2db528ac1a8538462239a72a1f1efa5e10cf/CMakeLists.txt#L45-L50)

[LecrisUT]

CMAKE_EXPORT_PACKAGE_REGISTRY nope not setup, on the pyproject.toml everything is rather vanilla, and the current CMakeLists.txt does not mess with anything related to find_package.

The CMake way to do this is with the new-ish (3.24 IIRC) FindPackage + FetchContent integration:

Yeah, for proper dependencies I do use the FetchContent approach. But this is a special case where I want to use the bundled project instead, i.e. Spglib_python where that snippet is in is just the python bindings and it is a subproject/subdir of Spglib so that if the system installed Spglib is found use and link to it, otherwise use the bundled source files commit-locked to the current sources.