go/types, types2: add missing Unalias calls (clarification)

This change adds an Unalias call in applyTypeFunc and arrayPtrDeref.
At the moment this doesn't change anything or fix any bugs because
of the way these two functions are invoked, but that could change
in the future.

Also, manually reviewed all type assertions to Type types.

Excluding assertions to type parameters, no obvious issues
were found except for #67540 for which a separate fix is pending.

There are potential issues with assertions type parameters
which will be addressed in a follow-up CL.

For #67547.

Change-Id: I312268dc5e104f95b68f115f00aec3ec4c82e41f
Reviewed-on: https://go-review.googlesource.com/c/go/+/587156
Reviewed-by: Robert Findley <[email protected]>
Auto-Submit: Robert Griesemer <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>

Author: griesemer

src/cmd/compile/internal/types2/builtins.go

@@ -960,7 +960,7 @@ func hasVarSize(t Type, seen map[*Named]bool) (varSized bool) {
 // applyTypeFunc returns nil.
 // If x is not a type parameter, the result is f(x).
 func (check *Checker) applyTypeFunc(f func(Type) Type, x *operand, id builtinId) Type {
-	if tp, _ := x.typ.(*TypeParam); tp != nil {
+	if tp, _ := Unalias(x.typ).(*TypeParam); tp != nil {
 		// Test if t satisfies the requirements for the argument
 		// type and collect possible result types at the same time.
 		var terms []*Term
@@ -1026,7 +1026,7 @@ func makeSig(res Type, args ...Type) *Signature {
 // arrayPtrDeref returns A if typ is of the form *A and A is an array;
 // otherwise it returns typ.
 func arrayPtrDeref(typ Type) Type {
-	if p, ok := typ.(*Pointer); ok {
+	if p, ok := Unalias(typ).(*Pointer); ok {
 		if a, _ := under(p.base).(*Array); a != nil {
 			return a
 		}