Unclear how to evaluate a marker for a set of extras

This is possibly similar to #448, but I think it's a different use case. I'm not completely clear on what "operations" #448 is meant to cover, so apologies if I missed that this is already part of that discussion.

I have two requirements:

a_req = Requirement("a[b,c]")
a_dep = Requirement("foo; extra == 'b'")

I want to check whether a_dep should apply, given that I am looking at it in the context of a_req. So, I have a set of extras, and I want to evaluate a_dep.marker to see if any apply. In the given case, I expect to get True.

The simplest way I can see is any(a_dep.marker.evaluate(environment={"extra": e}) for e in a_req.extras).

Is that the best way of doing this? Would it be useful to have an additional argument to Marker.evaluate() that specified a set of extras to check - then I could do a_dep.marker.evaluate(extras=a_req.extras) which seems more natural.

Start by reading Marker.evaluate and the related discussion in issue #448; the issue does not name implementation files or tests. Determine whether evaluating a marker against a set of extras is already supported or needs an API decision, and consider the issue resolved when that behavior and its expected result are clearly established.