flit-core: pyproject.toml missing dependencies on toml and tomli

[adamjstewart]

@takluyver I'm updating Spack's flit and flit-core packages and I noticed that flit-core's pyproject.toml does not list any dependencies. However, tomli (and possibly toml?) seem to be required to use flit-core. Is that correct? Should these be explicitly listed in the pyproject.toml? I realize that there's a cyclic dependency between flit-core and tomli, is this the reason this dependency isn't listed?

[takluyver]

You're right, tomli is required (it replaced toml from Flit version 3.4).

There's actually no metadata at all in flit_core's pyproject.toml, precisely because we'd need a TOML parser to read it. The metadata that would normally be there is embedded in the code instead:

flit/flit_core/flit_core/build_thyself.py

Lines 19 to 36 in ec6e6b7

	metadata_dict = {
	"name": "flit_core",
	"version": __version__,
	"author": "Thomas Kluyver & contributors",
	"author_email": "thomas@kluyver.me.uk",
	"home_page": "https://github.com/pypa/flit",
	"summary": (
	"Distribution-building parts of Flit. " "See flit package for more information"
	),
	"requires_dist": [
	"tomli",
	],
	'requires_python': '>=3.6',
	'classifiers': [
	"License :: OSI Approved :: BSD License",
	"Topic :: Software Development :: Libraries :: Python Modules",
	]
	}

The cyclic dependency is a bit of a pain. My current best idea for how to deal with it is described on the bootstrapping page. But there's a (long) ongoing discussion about this, e.g. #462, #481, #483.

[adamjstewart]

Thanks, that explains it. I think it still might be useful to include in the pyproject.toml for humans to read, but I'll leave that up to you. For what it's worth, in Spack our bootstrapping strategy is to download a copy of the flit-core source code when building tomli but not installing flit-core, and having a dependency on tomli in the flit-core package.

[pradyunsg]

The other option is putting a comment in the pyproject.toml file, stating where to find the data + a link to the above comment. :)

Do you want to file a PR?