go/types, types2: cannot handle partially instantiated generic function argument

[griesemer]

package p

func f(func(int) string) {}

func g[P, Q any](P) Q { var q Q; return q }

func _() {
	f(g)      // ok
	f(g[int]) // ERROR: cannot infer Q

	var _ func(int) string = g      // ok
	var _ func(int) string = g[int] // ok
}

The type-checker currently cannot handle a partially instantiated generic function argument.
Would be good to fix for 1.21 but not a release blocker.

[gopherbot]

Change https://go.dev/cl/494116 mentions this issue: go/types, types2: permit partially instantiated functions as function arguments