go/types, types2: explicitly look for nil type arguments in infer
Don't assume we have all type arguments if the number of type arguments
matches the number of type parameters. Instead, look explicitly for nil
type arguments in the provided targs.
Preparation for type inference with type arguments provided for type
parameters of generic function arguments passed to other functions.
For #59338.
Change-Id: I00918cd5ed06ae3277b4e41a3641063e0f53fef0
Reviewed-on: https://go-review.googlesource.com/c/go/+/494115 Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
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