go.tools/go/types: range iteration variables are typed (not untyped)

R=adonovan
CC=golang-dev
https://golang.org/cl/14516044

go/types/stmt.go

@@ -511,18 +511,18 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 		switch typ := x.typ.Underlying().(type) {
 		case *Basic:
 			if isString(typ) {
-				key = Typ[UntypedInt]
+				key = Typ[Int]
-				val = Typ[UntypedRune]
+				val = Typ[Rune]
 			}
 		case *Array:
-			key = Typ[UntypedInt]
+			key = Typ[Int]
 			val = typ.elt
 		case *Slice:
-			key = Typ[UntypedInt]
+			key = Typ[Int]
 			val = typ.elt
 		case *Pointer:
 			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
-				key = Typ[UntypedInt]
+				key = Typ[Int]
 				val = typ.elt
 			}
 		case *Map:

go/types/testdata/stmt0.src

@@ -507,7 +507,7 @@ func typeswitch2() {
    }
 }
 
-func rangeloops() {
+func rangeloops1() {
 	var (
 		x int
 		a [10]float32
@@ -612,6 +612,26 @@ func rangeloops() {
 	}
 }
 
+func rangeloops2() {
+	type I int
+	type R rune
+
+	var a [10]int
+	var i I
+	_ = i
+	for i /* ERROR cannot assign */ = range a {}
+	for i /* ERROR cannot assign */ = range &a {}
+	for i /* ERROR cannot assign */ = range a[:] {}
+
+	var s string
+	var r R
+	_ = r
+	for i /* ERROR cannot assign */ = range s {}
+	for i /* ERROR cannot assign */ = range "foo" {}
+	for _, r /* ERROR cannot assign */ = range s {}
+	for _, r /* ERROR cannot assign */ = range "foo" {}
+}
+
 func labels0() {
 	goto L0
 	goto L1