go.tools/go/types: fix ... parameter passing

Also: exclude test case from std test to fix build.

Fixes golang/go#6344.

R=adonovan
CC=golang-dev
https://golang.org/cl/13630043

go/types/call.go

@@ -143,7 +143,7 @@ func (check *checker) argument(sig *Signature, i int, x *operand, passSlice bool
 		typ = sig.params.vars[n-1].typ
 		if debug {
 			if _, ok := typ.(*Slice); !ok {
-				check.dump("%s: expected slice type, got %s", sig.params.vars[n-1].Pos(), typ)
+				check.dump("%s: expected unnamed slice type, got %s", sig.params.vars[n-1].Pos(), typ)
 			}
 		}
 	default:
@@ -157,7 +157,7 @@ func (check *checker) argument(sig *Signature, i int, x *operand, passSlice bool
 			check.errorf(x.pos(), "can only use ... with matching parameter")
 			return
 		}
-		if _, ok := x.typ.(*Slice); !ok {
+		if _, ok := x.typ.Underlying().(*Slice); !ok {
 			check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
 			return
 		}

go/types/stdlib_test.go

@@ -121,6 +121,7 @@ func TestStdfixed(t *testing.T) {
 		"bug373.go",    // TODO(gri) implement use checks
 		"bug376.go",    // TODO(gri) built-ins must be called (no built-in function expressions)
 		"issue3924.go", // TODO(gri) && and || produce bool result (not untyped bool)
+		"issue4847.go", // TODO(gri) initialization cycle error not found
 	)
 }
 

go/types/testdata/expr3.src

@@ -380,3 +380,9 @@ func _calls() {
 	fi(0, g2)
 	fi(0, g2 /* ERROR "2-valued expression" */ ())
 }
+
+func issue6344() {
+	type T []interface{}
+	var x T
+	fi(x...) // ... applies also to named slices
+}