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Auto merge of #27215 - pnkfelix:fsk-placer-take-5-just-in, r=nikomatsakis

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Macro desugaring of `in PLACE { BLOCK }` into "simpler" expressions following the in-development "Placer" protocol.

Includes Placer API that one can override to integrate support for `in` into one's own type.  (See [RFC 809].)

[RFC 809]: https://github.com/rust-lang/rfcs/blob/master/text/0809-box-and-in-for-stdlib.md

Part of #22181

Replaced PR #26180.

Turns on the `in PLACE { BLOCK }` syntax, while leaving in support for the old `box (PLACE) EXPR` syntax (since we need to support that at least until we have a snapshot with support for `in PLACE { BLOCK }`.

(Note that we are not 100% committed to the `in PLACE { BLOCK }` syntax.  In particular I still want to play around with some other alternatives.  Still, I want to get the fundamental framework for the protocol landed so we can play with implementing it for non `Box` types.)

----

Also, this PR leaves out support for desugaring-based `box EXPR`.  We will hopefully land that in the future, but for the short term there are type-inference issues injected by that change that we want to resolve separately.
This commit is contained in:
bors 2015-07-24 10:12:20 +00:00
commit 9413a926fc
28 changed files with 899 additions and 47 deletions
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45
src/libsyntax/parse/parser.rs
View file

@ -2612,18 +2612,43 @@ impl<'a> Parser<'a> {
ex = ExprAddrOf(m, e);
}
token::Ident(_, _) => {
if !self.check_keyword(keywords::Box) {
if !self.check_keyword(keywords::Box) && !self.check_keyword(keywords::In) {
return self.parse_dot_or_call_expr();
}
let lo = self.span.lo;
let box_hi = self.span.hi;
let keyword_hi = self.span.hi;
let is_in = self.token.is_keyword(keywords::In);
try!(self.bump());
// Check for a place: `box(PLACE) EXPR`.
if is_in {
let place = try!(self.parse_expr_res(Restrictions::RESTRICTION_NO_STRUCT_LITERAL));
let blk = try!(self.parse_block());
hi = blk.span.hi;
let blk_expr = self.mk_expr(blk.span.lo, blk.span.hi, ExprBlock(blk));
ex = ExprBox(Some(place), blk_expr);
return Ok(self.mk_expr(lo, hi, ex));
}
// FIXME (#22181) Remove `box (PLACE) EXPR` support
// entirely after next release (enabling `(box (EXPR))`),
// since it will be replaced by `in PLACE { EXPR }`, ...
//
// ... but for now: check for a place: `box(PLACE) EXPR`.
if try!(self.eat(&token::OpenDelim(token::Paren)) ){
// Support `box() EXPR` as the default.
// SNAP d4432b3
// Enable this warning after snapshot ...
//
// let box_span = mk_sp(lo, self.last_span.hi);
// self.span_warn(
// box_span,
// "deprecated syntax; use the `in` keyword now \
// (e.g. change `box (<expr>) <expr>` to \
// `in <expr> { <expr> }`)");
// Continue supporting `box () EXPR` (temporarily)
if !try!(self.eat(&token::CloseDelim(token::Paren)) ){
let place = try!(self.parse_expr_nopanic());
try!(self.expect(&token::CloseDelim(token::Paren)));
@ -2634,10 +2659,15 @@ impl<'a> Parser<'a> {
self.span_err(span,
&format!("expected expression, found `{}`",
this_token_to_string));
let box_span = mk_sp(lo, box_hi);
// Spanning just keyword avoids constructing
// printout of arg expression (which starts
// with parenthesis, as established above).
let box_span = mk_sp(lo, keyword_hi);
self.span_suggestion(box_span,
"try using `box()` instead:",
"box()".to_string());
"try using `box ()` instead:",
format!("box ()"));
self.abort_if_errors();
}
let subexpression = try!(self.parse_prefix_expr());
@ -2650,6 +2680,7 @@ impl<'a> Parser<'a> {
// Otherwise, we use the unique pointer default.
let subexpression = try!(self.parse_prefix_expr());
hi = subexpression.span.hi;
// FIXME (pnkfelix): After working out kinks with box
// desugaring, should be `ExprBox(None, subexpression)`
// instead.