go/types: Info.Instances is underpopulated

[adonovan]

Examining this program in the go/types playground (golang.org/x/tools/go/types/internal/play), which was recently augmented to show Info.Instances when the selection is an ast.Ident, the only identifier that has an entry in that map is the reference to Method (it has TypeArgs=[int] and Type=func(C[string])). Notably, there is no entry for either of the two references to Func. That seems like a bug.

package main

type C[T any] struct{}

func (C[T]) M()
func (C[T]) Method[U any]() {}

var _ = C[string].M
var _ = C[string].Method[int]

func Func[T any](T) {}

var _ = Func[int]
var _ = Func(1)

@griesemer @mrkfrmn