swift

4b8068d1 - [runtime] Handle same-type constraints when resolving generic params

[runtime] Handle same-type constraints when resolving generic params Generic parameters for a context are normally classified as "key", meaning they have actual metadata provided at runtime, or non-key, meaning they're derivable from somewhere else. However, a nested context or constrained extension can take what would be a "key" parameter in a parent context and make it non-key in a child context. This messes with the mapping between the (depth, index) representation of generic parameters and the flat list of generic arguments. Fix this by (1) consistently substituting out extension contexts with the contexts of the extended types, and (2) using the most nested context to decide which parameters are key, instead of the context a parameter was originally introduced in. Note that (1) may have problems if/when extensions start introducing their /own/ generic parameters. For now I tried to be consistent with what was there. rdar://problem/52364601