36     //     let _ = match x {} - 1;  // no parens
44     //     Example: `let _ = $match - 1;`
74     //         _ => m! {} - 1,  // binary subtraction operator
90     //         _ => m! {} - 1,  // no parens
98     //     if let _ = (Struct {}) {}  // needs parens
101     //         () if let _ = Struct {} => {}  // no parens
127     //     let _ = (return) - 1;  // without paren, this would return -1
129     //     let _ = return + 1;  // no paren because '+' cannot begin expr
136     //     let _ = 1 + return 1;  // no parens if rightmost subexpression
138     //     let _ = 1 + (return 1) + 1;  // needs parens
145     //     let _ = x as u8 + T;
147     //     let _ = (x as u8) < T;
360             _ => default_prec <= self.previous_operator,  in rightmost_subexpression_precedence()
363             _ => !self.next_operator_can_begin_expr,  in rightmost_subexpression_precedence()
381             || ((self.stmt || self.leftmost_subexpression_in_stmt) && matches!(expr, Expr::Let(_)))  in parenthesize()
384             || (self.condition && matches!(expr, Expr::Struct(_)))  in parenthesize()
396                         | Expr::Path(_)  in parenthesize()
424                 Expr::Break(_)  in precedence()
425                 | Expr::Closure(_)  in precedence()
426                 | Expr::Let(_)  in precedence()
427                 | Expr::Return(_)  in precedence()
428                 | Expr::Yield(_) => {  in precedence()
432                 _ => {}  in precedence()
483         Expr::Assign(_) => fixup.previous_operator <= Precedence::Assign,  in scan_left()
488         Expr::Cast(_) => fixup.previous_operator < Precedence::Cast,  in scan_left()
490         _ => true,  in scan_left()
504         _ => precedence < fixup.next_operator,  in scan_right()
518                 _ => bailout_offset >= 1,  in scan_right()
529                     _ => 1,  in scan_right()
547                 _ => bailout_offset >= 1,  in scan_right()
562                     _ => 1,  in scan_right()
589                 _ => bailout_offset >= 1,  in scan_right()
600                     _ => 1,  in scan_right()
631                         _ => 1,  in scan_right()
635                     (Scan::Fail, _) => false,  in scan_right()
637                     (Scan::Bailout | Scan::Consume, _) => true,  in scan_right()
668                 _ => Scan::Consume,  in scan_right()
685                 _ => Scan::Consume,  in scan_right()
726                 _ => {}  in scan_right()
736         Expr::Array(_)  in scan_right()
737         | Expr::Assign(_)  in scan_right()
738         | Expr::Async(_)  in scan_right()
739         | Expr::Await(_)  in scan_right()
740         | Expr::Binary(_)  in scan_right()
741         | Expr::Block(_)  in scan_right()
742         | Expr::Call(_)  in scan_right()
743         | Expr::Cast(_)  in scan_right()
744         | Expr::Const(_)  in scan_right()
745         | Expr::Continue(_)  in scan_right()
746         | Expr::Field(_)  in scan_right()
747         | Expr::ForLoop(_)  in scan_right()
748         | Expr::Group(_)  in scan_right()
749         | Expr::If(_)  in scan_right()
750         | Expr::Index(_)  in scan_right()
751         | Expr::Infer(_)  in scan_right()
752         | Expr::Lit(_)  in scan_right()
753         | Expr::Loop(_)  in scan_right()
754         | Expr::Macro(_)  in scan_right()
755         | Expr::Match(_)  in scan_right()
756         | Expr::MethodCall(_)  in scan_right()
757         | Expr::Paren(_)  in scan_right()
758         | Expr::Path(_)  in scan_right()
759         | Expr::Range(_)  in scan_right()
760         | Expr::Repeat(_)  in scan_right()
761         | Expr::Struct(_)  in scan_right()
762         | Expr::Try(_)  in scan_right()
763         | Expr::TryBlock(_)  in scan_right()
764         | Expr::Tuple(_)  in scan_right()
765         | Expr::Unsafe(_)  in scan_right()
766         | Expr::Verbatim(_)  in scan_right()
767         | Expr::While(_) => match fixup.next_operator {  in scan_right()
769             _ if precedence == Precedence::Let && fixup.next_operator < Precedence::Let => {  in scan_right()
772             _ => consume_by_precedence,  in scan_right()