Adding a non-metadata installer-only `dev-dependencies` table to pyproject.toml

[nicholdav (David Nicholson)]

I get why @pradyunsg thinks using optional-dependencies for this is “dumb” – it feels weird that a user could install tests as an 'extra" – but my impression from the maybe-not-a-duplicate-topic was that a lot of people maintaining downstream package managers actually use this to run tests (edit: without building and inspecting an sdist)?

Like @CAM-Gerlach was saying here:

Providing a way to specify how to run tests (and docs?)

Repackagers and other downstreams (the main case we’re discussing here) aren’t going to want to (and often, their policies would not allow) creating a separate virtual environment and using pip to install packages from the internet into it, just so they can introspect it to determine what gets installed and figure out how to replicate it in their own environment. Of course, they can build the package at least to a sdist and then extract the extra’s dependencies from the core metadata in the PKG…

Would they lose this ability if there was a dev-dependencies table then?
Sorry if this is just revealing my ignorance about what one can get out of a distrib package