go/types, types2: consider methods when unifying type parameters and constraints
An inferred type argument must implement its type parameter's constraint's
methods whether or not a core type exists. This allows us to infer type
parameters used in method signatures.
Fixes #51593.
Change-Id: I1fddb05a71d442641b4311d8e30a13ea9bdb4db5
Reviewed-on: https://go-review.googlesource.com/c/go/+/472298
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>