setup.py: introduce TRITON_OFFLINE_BUILD

[SomeoneSerge]

In e.g. Nixpkgs (probably in other similar distributions as well) it's important to be able to inject dependencies rather than use vendored/locked dependencies. When we fail to provide complete dependencies for triton we want to get an immediate error, rather than an attempt to download a substitute from the internet (which fails after a timeout anyway, because we the actual builds offline). Sometimes we'd also try to override a recipe with a different version of a dependency than declared upstream, so e.g. we tend to treat strict semantic version checking as an optional feature.

This PR proposes an additional boolean environment variable meant to disable vendoring and fetching attempts in favour of either an immediate error ("input declared but not defined") or a later compile/link time error.

I'm happy to maintain a patch on the Nixpkgs side as well if you think this doesn't belong in your repo.

I'm waiting for the builds to finish.

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[ThomasRaoux]

I'm a bit concerned about adding yet another build mode that would be untested in CI although I'm not sure I fully understand what it is trying to do. Is it just to get different version of NV tools and LLVM? There are already environment variable for that. Why does this not work for you?

[SomeoneSerge]

There are already environment variable for that. Why does this not work for you?

That used to be sufficient when Package.syspath_var_name was first introduced. Now get_thirdparty_packages and get_thirdparty_packages have grown to implement more logic, in particular the version/url checks, so we're back to deciding on what is the proper way to skip over these branches:

triton/python/setup.py

Line 224 in ff7c691

(not os.path.exists(version_file_path) or Path(version_file_path).read_text() != p.url):

triton/python/setup.py

Lines 261 to 265 in ff7c691

	download = not os.path.exists(src_path)
	if os.path.exists(dst_path) and system == "Linux" and shutil.which(dst_path) is not None:
	curr_version = subprocess.check_output([dst_path, "--version"]).decode("utf-8").strip()
	curr_version = re.search(r"V([.|\d]+)", curr_version).group(1)
	download = download or curr_version != version

A universal knob to make things "offline or fail" is the logical solution looking through our lense, but we're happy to adjust