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| author | bors <bors@rust-lang.org> | 2015-02-07 18:20:55 +0000 |
|---|---|---|
| committer | bors <bors@rust-lang.org> | 2015-02-07 18:20:55 +0000 |
| commit | 61626b306314768b273892e3a547b896ef7a4dfd (patch) | |
| tree | fccabe06769bf28388471d950fa4cd55da128a53 /src/libsyntax | |
| parent | ce5aad2f107e79c5f1baab40aff35b7899322d94 (diff) | |
| parent | b445bf2bd1139236fd815bf93610ddaf17726111 (diff) | |
| download | rust-61626b306314768b273892e3a547b896ef7a4dfd.tar.gz rust-61626b306314768b273892e3a547b896ef7a4dfd.zip | |
Auto merge of #21984 - pnkfelix:make-for-loops-a-terminating-scope, r=nikomatsakis
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 @nikomatsakis (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]
Diffstat (limited to 'src/libsyntax')
| -rw-r--r-- | src/libsyntax/ext/expand.rs | 28 |
1 files changed, 20 insertions, 8 deletions
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs index 33712dae900..f9d8406b845 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) => { |