go.tools/go/types: address and slice operations are not addressable

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/89380044

go/types/expr.go

@@ -84,14 +84,12 @@ func (check *checker) unary(x *operand, op token.Token) {
 	case token.AND:
 		// spec: "As an exception to the addressability
 		// requirement x may also be a composite literal."
-		if _, ok := unparen(x.expr).(*ast.CompositeLit); ok {
+		if _, ok := unparen(x.expr).(*ast.CompositeLit); !ok && x.mode != variable {
-			x.mode = variable
-		}
-		if x.mode != variable {
 			check.invalidOp(x.pos(), "cannot take address of %s", x)
 			x.mode = invalid
 			return
 		}
+		x.mode = value
 		x.typ = &Pointer{base: x.typ}
 		return
 
@@ -1228,7 +1226,6 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 				}
 				// spec: "For untyped string operands the result
 				// is a non-constant value of type string."
-				x.mode = value
 				if typ.kind == UntypedString {
 					x.typ = Typ[String]
 				}
@@ -1247,13 +1244,11 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
 				valid = true
 				length = typ.len
-				x.mode = variable
 				x.typ = &Slice{elem: typ.elem}
 			}
 
 		case *Slice:
 			valid = true
-			x.mode = variable
 			// x.typ doesn't change
 		}
 
@@ -1262,6 +1257,8 @@ func (check *checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 			goto Error
 		}
 
+		x.mode = value
+
 		// spec: "Only the first index may be omitted; it defaults to 0."
 		if slice3(e) && (e.High == nil || sliceMax(e) == nil) {
 			check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")

go/types/testdata/expr0.src

@@ -21,6 +21,7 @@ var (
 	b10 = &true /* ERROR "cannot take address" */
 	b11 = &b0
 	b12 = <-b0 /* ERROR "cannot receive" */
+	b13 = & & /* ERROR "cannot take address" */ b0
 
 	// int
 	i0 = 1

go/types/testdata/expr3.src

@@ -44,6 +44,7 @@ func indexes() {
 	_ = a[10:0:10] /* ERROR "invalid slice indices" */
 	_ = a[0:10:0] /* ERROR "invalid slice indices" */
 	_ = a[10:0:0] /* ERROR "invalid slice indices" */
+	_ = &a /* ERROR "cannot take address" */ [:10]
 
 	pa := &a
 	_ = pa[9]
@@ -61,6 +62,7 @@ func indexes() {
 	_ = pa[10:0:10] /* ERROR "invalid slice indices" */
 	_ = pa[0:10:0] /* ERROR "invalid slice indices" */
 	_ = pa[10:0:0] /* ERROR "invalid slice indices" */
+	_ = &pa /* ERROR "cannot take address" */ [:10]
 
 	var b [0]int
 	_ = b[0 /* ERROR "index .* out of bounds" */ ]
@@ -87,6 +89,7 @@ func indexes() {
 	_ = s[10:0:10] /* ERROR "invalid slice indices" */
 	_ = s[0:10:0] /* ERROR "invalid slice indices" */
 	_ = s[10:0:0] /* ERROR "invalid slice indices" */
+	_ = &s /* ERROR "cannot take address" */ [:10]
 
 	var t string
 	_ = t[- /* ERROR "negative" */ 1]