Support `{root:uri}`-like workflow in `build-system.requires`

[LecrisUT]

Consider a project with multiple sub-packages that depend on each other through their cmake find_package. We want that during the build step with isolation the appropriate dependency is used:

• when built from sdist: use the PyPI index
• when built from local git checkout: use relative path pointer
• when built from git url/archive: same as local checkout (if possible)

Borrowing hatch's {root:uri} the effective pyproject.toml would look like

[build-system]
requires = [ "foo >=1.0 @ {root:uri}/../bar" ]

Afaiu this is not possible because the pip/uv fronted would have to recognise that pattern and it would not be acceptable on PyPI.

But we have dynamically inserted build-system.requires, so wouldn't it be possible to expose that on a tool.scikit-build field and expand it with or without the @ qualifier?

[henryiii]

Do you have a link to the hatchling feature? We ultimately have to report a valid package specifier that is passed to pip/uv/etc, but I believe with overrides (we already have if.from-sdist) all we'd need is a config option for a package to add to the dynamic requirement list.

[LecrisUT]

Do you have a link to the hatchling feature?

• https://hatch.pypa.io/latest/config/dependency/#local (the tip box)
• https://github.com/pypa/hatch/blob/64031c1cf5d02d85203f68cb7a4fd5db2aa7a004/backend/src/hatchling/utils/context.py#L41-L43

Basically they resolve the paths to file: before handing over to the frontends. And I see that they only support file:, so if we focus only that form also, it should be easy to implement that translation as well.