Prevent setting an index as both explicit and default

[mkniewallner]

Unless I'm missing a use case, it seems to me that default = true won't actually do anything when set on an index that also sets explicit = true.

Consider for instance:

[project]
name = "foo"
version = "0.0.1"
dependencies = ["mypy==1.13.0"]

[[tool.uv.index]]
name = "test-pypi"
url = "https://test.pypi.org/simple"
explicit = true
default = true

default = true allows disabling default PyPi index, but in that specific case, it won't, which is expected, since the index is an explicit one, so mypy will correctly be resolved from public PyPi.

If there really is no use case for having both explicit = true and default = true for an index, should uv error out, to better convey that this is not a real use case?

[charliermarsh]

I think this probably should be allowed.