bjoernager/rust
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adjust larger comment to include the body

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This commit is contained in:
Niko Matsakis 2019-09-17 04:47:54 -04:00
parent 716b2bcfb3
commit 2d8b10f63c
1 changed files with 10 additions and 10 deletions
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20
src/librustc/hir/lowering/item.rs
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@ -1099,8 +1099,7 @@ impl LoweringContext<'_> {
// from:
//
// async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
// async move {
// }
// <body>
// }
//
// into:
@ -1113,11 +1112,19 @@ impl LoweringContext<'_> {
// let <pattern> = __arg1;
// let __arg0 = __arg0;
// let <pattern> = __arg0;
// drop-temps { <body> } // see comments later in fn for details
// }
// }
//
// If `<pattern>` is a simple ident, then it is lowered to a single
// `let <pattern> = <pattern>;` statement as an optimization.
//
// Note that the body is embedded in `drop-temps`; an
// equivalent desugaring would be `return { <body>
// };`. The key point is that we wish to drop all the
// let-bound variables and temporaries created in the body
// (and its tail expression!) before we drop the
// parameters (c.f. rust-lang/rust#64512).
for (index, parameter) in decl.inputs.iter().enumerate() {
let parameter = this.lower_param(parameter);
let span = parameter.pat.span;
@ -1231,7 +1238,7 @@ impl LoweringContext<'_> {
ThinVec::new(),
);
// Create a block like
// As noted above, create the final block like
//
// ```
// {
@ -1240,13 +1247,6 @@ impl LoweringContext<'_> {
// drop-temps { <user-body> }
// }
// ```
//
// This construction is carefully calibrated to
// get the drop-order correct. In particular, the
// drop-temps ensures that any temporaries in the
// tail expression of `<user-body>` are dropped
// *before* the parameters are dropped (see
// rust-lang/rust#64512).
let body = this.block_all(
desugared_span,
statements.into(),