[dev.go2go] go/types: don't rely on completed interfaces in isParameterized predicate

Also, take type lists into account when computing predicate.
Addresses crash #27 of #39634.

Updates #39634.

Change-Id: Id6e1d0d86ac1cb9d79828a3b5fdfbeba0e6aace0
Reviewed-on: https://go-review.googlesource.com/c/go/+/240902
Reviewed-by: Robert Griesemer <[email protected]>

Author: griesemer

src/go/types/fixedbugs/issue39634.go2

@@ -42,3 +42,7 @@ func F20(type t Z20)() { F20(t /* ERROR invalid composite literal type */ {}) }
 // crash 21
 type Z21 /* ERROR illegal cycle */ interface{ Z21 }
 func F21(type *T Z21)() { ( /* ERROR not used */ F21(Z21)) }
+
+// crash 27
+func e27(type T)() interface{ (x27 /* ERROR not a type */ ) }
+func x27() { e27() /* ERROR cannot infer T */ }

src/go/types/infer.go

@@ -212,13 +212,25 @@ func isParameterized(typ Type, seen map[Type]bool) (res bool) {
 		return isParameterized(t.params, seen) || isParameterized(t.results, seen)
 
 	case *Interface:
-		t.assertCompleteness()
-		for _, m := range t.allMethods {
-			if isParameterized(m.typ, seen) {
-				return true
+		if t.allMethods != nil {
+			// interface is complete - quick test
+			for _, m := range t.allMethods {
+				if isParameterized(m.typ, seen) {
+					return true
+				}
 			}
+			return isParameterizedList(unpack(t.allTypes), seen)
 		}
 
+		return t.iterate(func(t *Interface) bool {
+			for _, m := range t.methods {
+				if isParameterized(m.typ, seen) {
+					return true
+				}
+			}
+			return isParameterizedList(unpack(t.types), seen)
+		}, nil)
+
 	case *Map:
 		return isParameterized(t.key, seen) || isParameterized(t.elem, seen)