Dylan DPC b79ad57ad7 Rollup merge of #102998 - nathanwhit:let-chains-drop-order, r=eholk ... Drop temporaries created in a condition, even if it's a let chain Fixes #100513. During the lowering from AST to HIR we wrap expressions acting as conditions in a `DropTemps` expression so that any temporaries created in the condition are dropped after the condition is executed. Effectively this means we transform ```rust if Some(1).is_some() { .. } ``` into (roughly) ```rust if { let _t = Some(1).is_some(); _t } { .. } ``` so that if we create any temporaries, they're lifted into the new scope surrounding the condition, so for example something along the lines of ```rust if { let temp = Some(1); let _t = temp.is_some(); _t }. ``` Before this PR, if the condition contained any let expressions we would not introduce that new scope, instead leaving the condition alone. This meant that in a let-chain like ```rust if get_drop("first").is_some() && let None = get_drop("last") { println!("second"); } else { .. } ``` the temporary created for `get_drop("first")` would be lifted into the _surrounding block_, which caused it to be dropped after the execution of the entire `if` expression. After this PR, we wrap everything but the `let` expression in terminating scopes. The upside to this solution is that it's minimally invasive, but the downside is that in the worst case, an expression with `let` exprs interspersed like ```rust if get_drop("first").is_some() && let Some(_a) = get_drop("fifth") && get_drop("second").is_some() && let Some(_b) = get_drop("fourth") { .. } ``` gets _multiple_ new scopes, roughly ```rust if { let _t = get_drop("first").is_some(); _t } && let Some(_a) = get_drop("fifth") && { let _t = get_drop("second").is_some(); _t } && let Some(_b) = get_drop("fourth") { .. } ``` so instead of all of the temporaries being dropped at the end of the entire condition, they will be dropped right after they're evaluated (before the subsequent `let` expr). So while I'd say the drop behavior around let-chains is _less_ surprising after this PR, it still might not exactly match what people might expect. For tests, I've just extended the drop order tests added in #100526. I'm not sure if that's the best way to go about it, though, so suggestions are welcome.		2022-10-15 15:45:32 +05:30
..
src	Rollup merge of #102998 - nathanwhit:let-chains-drop-order, r=eholk	2022-10-15 15:45:32 +05:30
Cargo.toml	Temporarily reinstate doctest=false	2022-10-05 09:53:49 +09:00