Abandon fastjet's build system and rewrite it in CMake

[matthewfeickert]

I think the time has come to CMake fastjet and submit a PR.

Originally posted by @lgray in #301 (comment)

While I'm not sure if the FastJet authors would be on-board with this, we would have the ability to just add CMake support which people can then use as they want I don't think that would require a restructure?

[matthewfeickert]

I see that there's something at least CMake related already on https://gitlab.com/fastjet/fastjet/-/merge_requests/4 which seems to be adding cmake.in configure files for downstream use. I think(?) that would be helpful for builds here, as that would allow for pulling in the FastJet config from a top level CMakeLists.txt file, but I would assume that it would still be good to have FastJet just support CMake in general.

@henryiii thoughts here?

[matthewfeickert]

An email response from the FastJet team RE: the idea of a contribution of adding CMake support:

It's something we've discussed as being of interest, but you guessed correctly regarding bandwidth! The main issue we see is that there are quite a few options in the current build system, and replicating them all would take some work and validation. Added to that, even though we're using CMake in other projects, I wouldn’t say we're as proficient in it as we would like to be. If at some point some of you are interested in contributing on this front, we'd be happy to try it out and give our thoughts.

[matthewfeickert]

First thing would probably be to migrate https://gitlab.com/fastjet/siscone to CMake and then to step through and migrate all the FastJet plugins https://gitlab.com/fastjet/fastjet/-/tree/master/plugins?ref_type=heads. Once those all work then FastJet itself could be migrated.

[matthewfeickert]

PR #4 provides a good summary (especially this bit #4 (comment)) of why this is needed as well and then also overviews why cgal is currently installed in such a terrible manner.

fastjet/setup.py

Lines 52 to 88 in 28ec47c

	zip_filename = DIR / pathlib.Path(CGAL_ZIP).parts[-1]
	with urllib.request.urlopen(CGAL_ZIP) as http_obj:
	with open(zip_filename, "wb") as file_obj:
	shutil.copyfileobj(http_obj, file_obj)
	with zipfile.ZipFile(zip_filename) as zip_obj:
	cgal_dir = DIR / zip_obj.namelist()[0]
	zip_obj.extractall(DIR)
	# Patch for segfault of LimitedWarning
	# For more info see https://github.com/scikit-hep/fastjet/pull/131
	subprocess.run(
	["patch", "src/ClusterSequence.cc", DIR / "patch_clustersequence.txt"],
	cwd=FASTJET,
	)
	# RPATH is set for shared libraries in the following locations:
	# * fastjet/
	# * fastjet/_fastjet_core/lib/
	# * fastjet/_fastjet_core/lib/python*/site-packages/
	_rpath = "'$$ORIGIN/_fastjet_core/lib:$$ORIGIN:$$ORIGIN/../..'"
	env = os.environ.copy()
	env["PYTHON"] = sys.executable
	env["PYTHON_INCLUDE"] = f'-I{sysconfig.get_path("include")}'
	env["CXXFLAGS"] = "-O3 -Bstatic -lgmp -Bdynamic -std=c++17"
	env["LDFLAGS"] = env.get("LDFLAGS", "") + f" -Wl,-rpath,{_rpath}"
	env["ORIGIN"] = "$ORIGIN" # if evaluated, it will still be '$ORIGIN'
	args = [
	f"--prefix={OUTPUT}",
	"--enable-thread-safety",
	"--disable-auto-ptr",
	"--enable-allcxxplugins",
	"--enable-cgal-header-only",
	"--enable-cgal",
	f"--with-cgaldir={cgal_dir}",