Add hir::GenericArg::Infer

[JulianKnodt]

In order to extend inference to consts, make an Infer type on hir::GenericArg.

[JulianKnodt]

r? @lcnr
I'm not sure if you intended for const inference to work here yet, I didn't add it (but can if it's already possible)

[JulianKnodt]

@rustbot label: +S-waiting-on-review

[JulianKnodt]

@rustbot label: +S-waiting-on-review -S-waiting-on-author

[lcnr]

after this r=me 😅 thanks for working on this ❤️

[lcnr]

for this to work you have to modify fn opt_const_param_of to also run for GenericArg::Infer, don't you?

For that we probably want to remove the filter(|arg| arg.is_const()) and such and instead look at all const and type parameters to find the right one. Feel free to either add a FIXME in that method or implement it in this PR

[JulianKnodt]

I changed them all to match on GenericArg::Infer | GenericArg::Const which may need to be changed since some code depends on matching on GenericParamDefKind::Const, but need to double check that

[lcnr]

this isn't quite right, further down we use the arg_index while filtering by matches!(param.kind, ty::GenericParamDefKind::Const { .. }) so we can get mismatches here. I think we want to filter with !arg.is_lifetime()

[JulianKnodt]

hm just changing it to lifetimes doesn't seem to work, is there any reason to filter later and instead just move the conditional into the position call: position(|a| matches!(a, Infer|Const) && ...)? and have nth(index)
(sorry, it's a bit late where I am so will get to this tmrw)

[lcnr]

you also have to modify the GenericParamKind filter when searching for the param in the generics.

[lcnr]

i.e. use !is_lifetime both when computing and when using the arg_index

[JulianKnodt]

I've been trying to finagle this, but it seems to be more annoying than this small change, so I'll just leave a FIXME

[lcnr]

@bors r=oli-obk,lcnr

[bors]

📌 Commit 8759f00 has been approved by oli-obk,lcnr

[lcnr]

while I assume it won't matter, better safe than sorry
@bors rollup=never

[bors]

⌛ Testing commit 8759f00 with merge cc4cb3f8f09c50d50407106fee4b008df6e11b1e...

[bors]

💔 Test failed - checks-actions

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[lcnr]

@bors retry

[bors]

⌛ Testing commit 8759f00 with merge fd853c0...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk,lcnr
Pushing fd853c0 to master...