Rollup merge of rust-lang#38956 - theduke:document-field-init-shorthand-38830, r=steveklabnik

Update struct_expr grammar for field init shorthand. Part of the work for rust-lang#38830 . r? @steveklabnik

Author: steveklabnik

src/doc/grammar.md

@@ -510,8 +510,9 @@ unit_expr : "()" ;
 ### Structure expressions
 
 ```antlr
-struct_expr : expr_path '{' ident ':' expr
- [ ',' ident ':' expr ] *
+struct_expr_field_init : ident | ident ':' expr ;
+struct_expr : expr_path '{' struct_expr_field_init
+ [ ',' struct_expr_field_init ] *
  [ ".." expr ] '}' |
  expr_path '(' expr
  [ ',' expr ] * ')' |