Handle Struct { box i } syntax

Named structs can have `box` patterns that will bind to their fields.
This is similar to the behavior of the `ref` and `mut` fields, but is at
least a little bit surprising.

Author: ecstatic-morse

crates/ra_parser/src/grammar/patterns.rs

@@ -162,6 +162,9 @@ fn record_field_pat_list(p: &mut Parser) {
             T![..] => p.bump(),
             IDENT if p.nth(1) == T![:] => record_field_pat(p),
             T!['{'] => error_block(p, "expected ident"),
+            T![box] => {
+                box_pat(p);
+            }
             _ => {
                 bind_pat(p, false);
             }
@@ -271,9 +274,6 @@ fn bind_pat(p: &mut Parser, with_at: bool) -> CompletedMarker {
 }
 
 // test box_pat
-// struct Outer;
-// struct Inner;
-//
 // fn main() {
 //     let box i = ();
 //     let box Outer { box i, j: box Inner(box &x) } = ();

crates/ra_syntax/test_data/parser/inline/ok/0143_box_pat.rs

@@ -1,2 +1,5 @@
-struct Outer;
-struct Inner;
+fn main() {
+    let box i = ();
+    let box Outer { box i, j: box Inner(box &x) } = ();
+    let box ref mut i = ();
+}