[WIP] [let_chains, 4/N] Introduce hir::ExprKind::Let
#68577
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disallowed positions is checked in ast_validation in next commit
rust-highfive
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Centril
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Jan 27, 2020
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| /// Emits an error banning the `let` expression provided in the given location. | ||
| fn ban_let_expr(&self, expr: &'a Expr) { |
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It's probably a better idea to move this to feature gating under e.g. #![feature(let_expr)] so that we can test ::Let more than what let_chains alone would allow. We could also move that, or the ast_validation logic, out of this PR and land it separately.
| @@ -513,33 +513,6 @@ warning: the feature `let_chains` is incomplete and may cause the compiler to cr | |||
| LL | #![feature(let_chains)] // Avoid inflating `.stderr` with overzealous gates in this test. | |||
| | ^^^^^^^^^^ | |||
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| error[E0658]: `match` is not allowed in a `const` | |||
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::Let can result in switching on the discriminant, like or-patterns. Alone however, it is not control flow. That said, we should probably gate let p = s here too?
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@bors try @rust-timer queue |
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Awaiting bors try build completion |
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⌛ Trying commit 6ed41a8 with merge 460f28a6daf1e5ebd90eb84972688220a0f03b6a... |
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The job Click to expand the log.I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact |
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Some notes that seem important:
struct D(usize);
impl Drop for D {
fn drop(&mut self) {
dbg!(self.0);
}
}
fn main() {
if let Some(d) = Some(D(0)) {
D(1);
}
D(2);
let mut x = Some(D(3));
while let Some(d) = x.take() {
D(4);
}
D(5);
}should result in: [src/main.rs:5] self.0 = 1
[src/main.rs:5] self.0 = 0
[src/main.rs:5] self.0 = 2
[src/main.rs:5] self.0 = 4
[src/main.rs:5] self.0 = 3
[src/main.rs:5] self.0 = 5That is: Note to self: Add a test for this!
match let Some(d) = Some(D(0)) {
// borrowck doesn't understand that `true` and the pattern matching conincide.
true => D(1),
_ => {} // make sure `d` is not available here.
}
D(2);
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☀️ Try build successful - checks-azure |
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Queued 460f28a6daf1e5ebd90eb84972688220a0f03b6a with parent 8a79d08, future comparison URL. |
JohnCSimon
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@Centril any updates? |
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Closing this for now. I'll need to think some more about how to make progress here. |
voidc
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bors
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Introduce `hir::ExprKind::Let` - Take 2 Builds on rust-lang#68577 and depends on rust-lang#79328. cc rust-lang#53667
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Introduces
hir::ExprKind::Let(&Pat<'_>, &Expr<'_>). That is, this introduceslet pat = exprexpressions.For now, this is very much WIP and probably depends on #67668 to remove the hacks in HAIR / region / generator_interior, but I thought it would be useful to have this open for discussion purposes and so that I can check perf.
cc #53667.
r? @matthewjasper cc @oli-obk