From b445bf2bd1139236fd815bf93610ddaf17726111 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Wed, 4 Feb 2015 13:24:44 +0100
Subject: [PATCH] make `for PAT in ITER_EXPR { ... }` a terminating-scope for
ITER_EXPR.
In effect, temporary anonymous values created during the evaluation of
ITER_EXPR no longer not live for the entirety of the block surrounding
the for-loop; instead they only live for the extent of the for-loop
itself, and no longer.
----
There is one case I know of that this breaks, demonstrated to me by
niko (but it is also a corner-case that is useless in practice). Here
is that case:
```
fn main() {
let mut foo: Vec<&i8> = Vec::new();
for i in &[1, 2, 3] { foo.push(i) }
}
```
Note that if you add any code following the for-loop above, or even a
semicolon to the end of it, then the code will stop compiling (i.e.,
it gathers a vector of references but the gathered vector cannot
actually be used.)
(The above code, despite being useless, did occur in one run-pass test
by accident; that test is updated here to accommodate the new
striction.)
----
So, technically this is a:
[breaking-change]
---
src/libsyntax/ext/expand.rs | 28 ++++++++++++++++-------
src/test/run-pass/loop-label-shadowing.rs | 2 +-
2 files changed, 21 insertions(+), 9 deletions(-)
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index eaee67f9a6174..d75766c608ba0 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -230,15 +230,18 @@ pub fn expand_expr(e: P<ast::Expr>, fld: &mut MacroExpander) -> P<ast::Expr> {
ast::ExprForLoop(pat, head, body, opt_ident) => {
// to:
//
- // match ::std::iter::IntoIterator::into_iter(<head>) {
- // mut iter => {
- // [opt_ident]: loop {
- // match ::std::iter::Iterator::next(&mut iter) {
- // ::std::option::Option::Some(<pat>) => <body>,
- // ::std::option::Option::None => break
+ // {
+ // let result = match ::std::iter::IntoIterator::into_iter(<head>) {
+ // mut iter => {
+ // [opt_ident]: loop {
+ // match ::std::iter::Iterator::next(&mut iter) {
+ // ::std::option::Option::Some(<pat>) => <body>,
+ // ::std::option::Option::None => break
+ // }
// }
// }
- // }
+ // };
+ // result
// }
// expand <head>
@@ -319,7 +322,16 @@ pub fn expand_expr(e: P<ast::Expr>, fld: &mut MacroExpander) -> P<ast::Expr> {
fld.cx.expr_call(span, fld.cx.expr_path(into_iter_path), vec![head])
};
- fld.cx.expr_match(span, into_iter_expr, vec![iter_arm])
+
+ let match_expr = fld.cx.expr_match(span, into_iter_expr, vec![iter_arm]);
+
+ // `{ let result = ...; result }`
+ let result_ident = token::gensym_ident("result");
+ fld.cx.expr_block(
+ fld.cx.block_all(
+ span,
+ vec![fld.cx.stmt_let(span, false, result_ident, match_expr)],
+ Some(fld.cx.expr_ident(span, result_ident))))
}
ast::ExprClosure(capture_clause, fn_decl, block) => {
diff --git a/src/test/run-pass/loop-label-shadowing.rs b/src/test/run-pass/loop-label-shadowing.rs
index 686a9a002cebf..d96ff869fa0ab 100644
--- a/src/test/run-pass/loop-label-shadowing.rs
+++ b/src/test/run-pass/loop-label-shadowing.rs
@@ -13,7 +13,7 @@
fn main() {
let mut foo = Vec::new();
'foo: for i in &[1, 2, 3] {
- foo.push(i);
+ foo.push(*i);
}
}