go/types: fix a bug with type instantiation

Change-Id: I977bb5525a40d0e17c27bbc01d7c77426e1bad00

src/go/types/subst.go

@@ -122,22 +122,25 @@ func (s *subster) typ(typ Type) (res Type) {
 		}
 
 	case *Named:
+		// if not all type parameters are known, create a parameterized type
+		if isParameterizedList(s.targs) {
+			return &Parameterized{t.obj, s.targs}
+		}
+
 		// TODO(gri) revisit name creation (function local types, etc.) and factor out
 		name := TypeString(t, nil) + "<" + typeListString(s.targs) + ">"
-		//s.check.dump("- %s => %s", t, name)
 		if tname, found := s.check.typMap[name]; found {
-			//s.check.dump("- found %s", tname)
 			return tname.typ
 		}
+
 		// create a new named type and populate caches to avoid endless recursion
 		// TODO(gri) should use actual instantiation position
 		tname := NewTypeName(t.obj.pos, s.check.pkg, name, nil)
 		s.check.typMap[name] = tname
 		named := NewNamed(tname, nil, nil)
 		s.cache[t] = named
-		//s.check.dump("- installed %s", tname)
 		named.underlying = s.typ(t.underlying).Underlying()
-		//s.check.dump("- finished %s", tname)
+
 		// instantiate custom methods as necessary
 		for _, m := range t.methods {
 			// methods may not have a fully set up signature yet

src/go/types/testdata/tmp.go2

@@ -1,13 +1,30 @@
-// Copyright 2019 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
 package p
 
-type S(type T) struct {
-        f T
+type Pair(type K) struct {
+	key K
 }
 
-func (r S(T)) m() T {
-        return r.f
-}
+type Receiver(type T) struct {
+	values T
+}
+
+type Iterator(type K) struct {
+	r Receiver(Pair(K))
+}
+
+func (r Receiver(T)) Values() T {
+	return r.values
+}
+
+func Values (type T) (r Receiver(T)) T {
+        return r.values
+}
+
+func (it Iterator(K)) Next() K {
+	// x := it.r.Values()
+        x := Values(Pair(K))(it.r)
+        // it         : Iterator(K)
+        // it.r       : Receiver(Pair(K))
+        // it.r.Values: Pair(K)
+	return x.key
+}

src/go/types/testdata/typeinst2.go2

@@ -56,3 +56,25 @@ func (l List(E)) Head() (_ E, _ bool) {
 	}
 	return
 }
+
+// A test case for instantiating types with other types (extracted from map.go2)
+
+type Pair(type K) struct {
+	key K
+}
+
+type Receiver(type T) struct {
+	values T
+}
+
+type Iterator(type K) struct {
+	r Receiver(Pair(K))
+}
+
+func Values (type T) (r Receiver(T)) T {
+        return r.values
+}
+
+func (it Iterator(K)) Next() K {
+        return Values(Pair(K))(it.r).key
+}