fix: box_syntax(#1412)

Change-Id: I6e20e0163fa545de37226c1561b3b7103615626c

crates/ra_parser/src/grammar/expressions.rs

@@ -583,3 +583,8 @@ pub(crate) fn named_field_list(p: &mut Parser) {
     p.expect(T!['}']);
     m.complete(p, NAMED_FIELD_LIST);
 }
+
+// test box_syntax
+// fn foo() {
+//     let x = box 1i32;
+// }

crates/ra_syntax/tests/data/parser/inline/ok/0132_box_syntax.rs

@@ -0,0 +1,3 @@
+fn foo() {
+    let x = box 1i32;
+}