Many of the modifications putting in `Box::new` calls also include a
pointer to Issue 22405, which tracks going back to `box <expr>` if
possible in the future.
(Still tried to use `Box<_>` where it sufficed; thus some tests still
have `box_syntax` enabled, as they use a mix of `box` and `Box::new`.)
Precursor for overloaded-`box` and placement-`in`; see Issue 22181.
In summary these are some example transitions this change makes:
'a || => ||: 'a
proc:Send() => proc():Send
The intended syntax for closures is to put the lifetime bound not at the front
but rather in the list of bounds. Currently there is no official support in the
AST for bounds that are not 'static, so this case is currently specially handled
in the parser to desugar to what the AST is expecting. Additionally, this moves
the bounds on procedures to the correct position, which is after the argument
list.
The current grammar for closures and procedures is:
procedure := 'proc' [ '<' lifetime-list '>' ] '(' arg-list ')'
[ ':' bound-list ] [ '->' type ]
closure := [ 'unsafe' ] ['<' lifetime-list '>' ] '|' arg-list '|'
[ ':' bound-list ] [ '->' type ]
lifetime-list := lifetime | lifetime ',' lifetime-list
arg-list := ident ':' type | ident ':' type ',' arg-list
bound-list := bound | bound '+' bound-list
bound := path | lifetime
This does not currently handle the << ambiguity in `Option<<'a>||>`, I am
deferring that to a later patch. Additionally, this removes the support for the
obsolete syntaxes of ~fn and &fn.
Closes#10553Closes#10767Closes#11209Closes#11210Closes#11211
