Reintroduce hir::ExprKind::If #79328
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r? @davidtwco (rust_highfive has picked a reviewer for you, use r? to override) |
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Why is this useful? |
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That issue says:
What changed since then? |
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I don't know exactly what changed since that time. Maybe someone better than me in this field could make a better explanation? |
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Lowering |
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☔ The latest upstream changes (presumably #79529) made this pull request unmergeable. Please resolve the merge conflicts. Note that reviewers usually do not review pull requests until merge conflicts are resolved! Once you resolve the conflicts, you should change the labels applied by bors to indicate that your PR is ready for review. Post this as a comment to change the labels: |
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@voidc You should see the above comment about dropping order |
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Tried to Also, these tests are windows related :/ |
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I've pushed the blessed test output |
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@matthewjasper Thanks! It is very kind of you I may have to face this scenario again in the future and if it does, should I spin-up a Windows environment to bless the tests? |
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I guess creating a Windows environment is the easiest way to bless these tests if you need to do it yourself. |
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☀️ Test successful - checks-actions |
This was referenced Jan 14, 2021
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Reintroduce hir::ExprKind::If Basically copied and paste rust-lang#59288/rust-lang/rust-clippy#4080 with some modifications. The vast majority of tests were fixed and now there are only a few remaining. Since I am still unable to figure out the missing pieces, any help with the following list is welcome. - [ ] **Unnecessary `typeck` exception**: [Cheated on this one to make CI green.](https://github.com/rust-lang/rust/pull/79328/files#diff-3faee9ba23fc54a12b7c43364ba81f8c5660045c7e1d7989a02a0cee1c5b2051) - [x] **Incorrect span**: [Span should reference `then` and `else` separately.](https://github.com/rust-lang/rust/pull/79328/files#diff-cf2c46e82222ee4b1037a68fff8a1af3c4f1de7a6b3fd798aacbf3c0475abe3d) - [x] **New note regarding `assert!`**: [Modified but not "wrong". Maybe can be a good thing?](https://github.com/rust-lang/rust/pull/79328/files#diff-9e0d7c89ed0224e2b62060c957177c27db43c30dfe3c2974cb6b5091cda9cfb5) - [x] **Inverted report location**: [Modified but not "wrong". Locations were inverted.](https://github.com/rust-lang/rust/pull/79328/files#diff-f637ce7c1f68d523a165aa9651765df05e36c4d7d279194b1a6b28b48a323691) - [x] **`src/test/ui/point-to-type-err-cause-on-impl-trait-return.rs` has weird errors**: [Not sure why this is happening.](https://github.com/rust-lang/rust/pull/79328/files#diff-c823c09660f5b112f95e97e8ff71f1797b6c7f37dbb3d16f8e98bbaea8072e95) - [x] **Missing diagnostic**: [???](https://github.com/rust-lang/rust/pull/79328/files#diff-6b8ab09360d725ba4513933827f9796b42ff9522b0690f80b76de067143af2fc)
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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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…shtriplett Stabilize `let_chains` in Rust 1.64 # Stabilization proposal This PR proposes the stabilization of `#![feature(let_chains)]` in a future-compatibility way that will allow the **possible** addition of the `EXPR is PAT` syntax. Tracking issue: rust-lang#53667 Version: 1.64 (beta => 2022-08-11, stable => 2022-10-22). ## What is stabilized The ability to chain let expressions along side local variable declarations or ordinary conditional expressions. For example: ```rust pub enum Color { Blue, Red, Violet, } pub enum Flower { Rose, Tulip, Violet, } pub fn roses_are_red_violets_are_blue_printer( (first_flower, first_flower_color): (Flower, Color), (second_flower, second_flower_color): (Flower, Color), pick_up_lines: &[&str], ) { if let Flower::Rose = first_flower && let Color::Red = first_flower_color && let Flower::Violet = second_flower && let Color::Blue = second_flower_color && let &[first_pick_up_line, ..] = pick_up_lines { println!("Roses are red, violets are blue, {}", first_pick_up_line); } } fn main() { roses_are_red_violets_are_blue_printer( (Flower::Rose, Color::Red), (Flower::Violet, Color::Blue), &["sugar is sweet and so are you"], ); } ``` ## Motivation The main motivation for this feature is improving readability, ergonomics and reducing paper cuts. For more examples, see the [RFC](https://github.com/rust-lang/rfcs/blob/master/text/2497-if-let-chains.md). ## What isn't stabilized * Let chains in match guards (`if_let_guard`) * Resolution of divergent non-terminal matchers * The `EXPR is PAT` syntax ## History * On 2017-12-24, [RFC: if- and while-let-chains](rust-lang/rfcs#2260) * On 2018-07-12, [eRFC: if- and while-let-chains, take 2](rust-lang/rfcs#2497) * On 2018-08-24, [Tracking issue for eRFC 2497, "if- and while-let-chains, take 2](rust-lang#53667) * On 2019-03-19, [Run branch cleanup after copy prop](rust-lang#59290) * On 2019-03-26, [Generalize diagnostic for x = y where bool is the expected type](rust-lang#59439) * On 2019-04-24, [Introduce hir::ExprKind::Use and employ in for loop desugaring](rust-lang#60225) * On 2019-03-19, [[let_chains, 1/6] Remove hir::ExprKind::If](rust-lang#59288) * On 2019-05-15, [[let_chains, 2/6] Introduce Let(..) in AST, remove IfLet + WhileLet and parse let chains](rust-lang#60861) * On 2019-06-20, [[let_chains, 3/6] And then there was only Loop](rust-lang#61988) * On 2020-11-22, [Reintroduce hir::ExprKind::If](rust-lang#79328) * On 2020-12-24, [Introduce hir::ExprKind::Let - Take 2](rust-lang#80357) * On 2021-02-19, [Lower condition of if expression before it's "then" block](rust-lang#82308) * On 2021-09-01, [Fix drop handling for `if let` expressions](rust-lang#88572) * On 2021-09-04, [Formally implement let chains](rust-lang#88642) * On 2022-01-19, [Add tests to ensure that let_chains works with if_let_guard](rust-lang#93086) * On 2022-01-18, [Introduce `enhanced_binary_op` feature](rust-lang#93049) * On 2022-01-22, [Fix `let_chains` and `if_let_guard` feature flags](rust-lang#93213) * On 2022-02-25, [Initiate the inner usage of `let_chains`](rust-lang#94376) * On 2022-01-28, [[WIP] Introduce ast::StmtKind::LetElse to allow the usage of `let_else` with `let_chains`](rust-lang#93437) * On 2022-02-26, [1 - Make more use of `let_chains`](rust-lang#94396) * On 2022-02-26, [2 - Make more use of `let_chains`](rust-lang#94400) * On 2022-02-27, [3 - Make more use of `let_chains`](rust-lang#94420) * On 2022-02-28, [4 - Make more use of `let_chains`](rust-lang#94445) * On 2022-02-28, [5 - Make more use of `let_chains`](rust-lang#94448) * On 2022-02-28, [6 - Make more use of `let_chains`](rust-lang#94465) * On 2022-03-01, [7 - Make more use of `let_chains`](rust-lang#94476) * On 2022-03-01, [8 - Make more use of `let_chains`](rust-lang#94484) * On 2022-03-01, [9 - Make more use of `let_chains`](rust-lang#94498) * On 2022-03-08, [Warn users about `||` in let chain expressions](rust-lang#94754) From the first RFC (2017-12-24) to the theoretical future stabilization day (2022-10-22), it can be said that this feature took 4 years, 9 months and 28 days of research, development, discussions, agreements and headaches to be settled. ## Divergent non-terminal matchers More specifically, rust-lang#86730. ```rust macro_rules! mac { ($e:expr) => { if $e { true } else { false } }; } fn main() { // OK! assert_eq!(mac!(true && let 1 = 1), true); // ERROR! Anything starting with `let` is not considered an expression assert_eq!(mac!(let 1 = 1 && true), true); } ``` To the best of my knowledge, such error or divergence is orthogonal, does not prevent stabilization and can be tackled independently in the near future or effectively in the next Rust 2024 edition. If not, then https://github.com/c410-f3r/rust/tree/let-macro-blah contains a set of changes that will consider `let` an expression. It is possible that none of the solutions above satisfies all applicable constraints but I personally don't know of any other plausible answers. ## Alternative syntax Taking into account the usefulness of this feature and the overwhelming desire to use both now and in the past, `let PAT = EXPR` will be utilized for stabilization but it doesn't or shall create any obstacle for a **possible** future addition of `EXPR is PAT`. The introductory snippet would then be written as the following. ```rust if first_flower is Flower::Rose && first_flower_color is Color::Red && second_flower is Flower::Violet && second_flower_color is Color::Blue && pick_up_lines is &[first_pick_up_line, ..] { println!("Roses are red, violets are blue, {}", first_pick_up_line); } ``` Just to reinforce, this PR only unblocks a **possible** future road for `EXPR is PAT` and does emphasize what is better or what is worse. ## Tests * [Verifies the drop order of let chains and ensures it won't change in the future in an unpredictable way](https://github.com/rust-lang/rust/blob/master/src/test/ui/mir/mir_let_chains_drop_order.rs) * [AST lowering does not wrap let chains in an `DropTemps` expression](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/ast-lowering-does-not-wrap-let-chains.rs) * [Checks pretty printing output](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/ast-pretty-check.rs) * [Verifies uninitialized variables due to MIR modifications](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/chains-without-let.rs) * [A collection of statements where `let` expressions are forbidden](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.rs) * [All or at least most of the places where let chains are allowed](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/feature-gate.rs) * [Ensures that irrefutable lets are allowed in let chains](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/irrefutable-lets.rs) * [issue-88498.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-88498.rs), [issue-90722.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-90722.rs), [issue-92145.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-92145.rs) and [issue-93150.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-93150.rs) were bugs found by third parties and fixed overtime. * [Indexing was triggering a ICE due to a wrongly constructed MIR graph](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/no-double-assigments.rs) * [Protects the precedence of `&&` in relation to other things](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/protect-precedences.rs) * [`let_chains`, as well as `if_let_guard`, has a valid MIR graph that evaluates conditional expressions correctly](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/then-else-blocks.rs) Most of the infra-structure used by let chains is also used by `if` expressions in stable compiler versions since rust-lang#80357 and rust-lang#88572. As a result, no bugs were found since the integration of rust-lang#88642. ## Possible future work * Let chains in match guards is implemented and working but stabilization is blocked by `if_let_guard`. * The usage of `let_chains` with `let_else` is possible but not implemented. Regardless, one attempt was introduced and closed in rust-lang#93437. Thanks `@Centril` for creating the RFC and huge thanks (again) to `@matthewjasper` for all the reviews, mentoring and MIR implementations. Fixes rust-lang#53667
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Sep 15, 2022
Stabilize `let_chains` in Rust 1.64
# Stabilization proposal
This PR proposes the stabilization of `#![feature(let_chains)]` in a future-compatibility way that will allow the **possible** addition of the `EXPR is PAT` syntax.
Tracking issue: #53667
Version: 1.64 (beta => 2022-08-11, stable => 2022-10-22).
## What is stabilized
The ability to chain let expressions along side local variable declarations or ordinary conditional expressions. For example:
```rust
pub enum Color {
Blue,
Red,
Violet,
}
pub enum Flower {
Rose,
Tulip,
Violet,
}
pub fn roses_are_red_violets_are_blue_printer(
(first_flower, first_flower_color): (Flower, Color),
(second_flower, second_flower_color): (Flower, Color),
pick_up_lines: &[&str],
) {
if let Flower::Rose = first_flower
&& let Color::Red = first_flower_color
&& let Flower::Violet = second_flower
&& let Color::Blue = second_flower_color
&& let &[first_pick_up_line, ..] = pick_up_lines
{
println!("Roses are red, violets are blue, {}", first_pick_up_line);
}
}
fn main() {
roses_are_red_violets_are_blue_printer(
(Flower::Rose, Color::Red),
(Flower::Violet, Color::Blue),
&["sugar is sweet and so are you"],
);
}
```
## Motivation
The main motivation for this feature is improving readability, ergonomics and reducing paper cuts.
For more examples, see the [RFC](https://github.com/rust-lang/rfcs/blob/master/text/2497-if-let-chains.md).
## What isn't stabilized
* Let chains in match guards (`if_let_guard`)
* Resolution of divergent non-terminal matchers
* The `EXPR is PAT` syntax
## History
* On 2017-12-24, [RFC: if- and while-let-chains](rust-lang/rfcs#2260)
* On 2018-07-12, [eRFC: if- and while-let-chains, take 2](rust-lang/rfcs#2497)
* On 2018-08-24, [Tracking issue for eRFC 2497, "if- and while-let-chains, take 2](rust-lang/rust#53667)
* On 2019-03-19, [Run branch cleanup after copy prop](rust-lang/rust#59290)
* On 2019-03-26, [Generalize diagnostic for x = y where bool is the expected type](rust-lang/rust#59439)
* On 2019-04-24, [Introduce hir::ExprKind::Use and employ in for loop desugaring](rust-lang/rust#60225)
* On 2019-03-19, [[let_chains, 1/6] Remove hir::ExprKind::If](rust-lang/rust#59288)
* On 2019-05-15, [[let_chains, 2/6] Introduce Let(..) in AST, remove IfLet + WhileLet and parse let chains](rust-lang/rust#60861)
* On 2019-06-20, [[let_chains, 3/6] And then there was only Loop](rust-lang/rust#61988)
* On 2020-11-22, [Reintroduce hir::ExprKind::If](rust-lang/rust#79328)
* On 2020-12-24, [Introduce hir::ExprKind::Let - Take 2](rust-lang/rust#80357)
* On 2021-02-19, [Lower condition of if expression before it's "then" block](rust-lang/rust#82308)
* On 2021-09-01, [Fix drop handling for `if let` expressions](rust-lang/rust#88572)
* On 2021-09-04, [Formally implement let chains](rust-lang/rust#88642)
* On 2022-01-19, [Add tests to ensure that let_chains works with if_let_guard](rust-lang/rust#93086)
* On 2022-01-18, [Introduce `enhanced_binary_op` feature](rust-lang/rust#93049)
* On 2022-01-22, [Fix `let_chains` and `if_let_guard` feature flags](rust-lang/rust#93213)
* On 2022-02-25, [Initiate the inner usage of `let_chains`](rust-lang/rust#94376)
* On 2022-01-28, [[WIP] Introduce ast::StmtKind::LetElse to allow the usage of `let_else` with `let_chains`](rust-lang/rust#93437)
* On 2022-02-26, [1 - Make more use of `let_chains`](rust-lang/rust#94396)
* On 2022-02-26, [2 - Make more use of `let_chains`](rust-lang/rust#94400)
* On 2022-02-27, [3 - Make more use of `let_chains`](rust-lang/rust#94420)
* On 2022-02-28, [4 - Make more use of `let_chains`](rust-lang/rust#94445)
* On 2022-02-28, [5 - Make more use of `let_chains`](rust-lang/rust#94448)
* On 2022-02-28, [6 - Make more use of `let_chains`](rust-lang/rust#94465)
* On 2022-03-01, [7 - Make more use of `let_chains`](rust-lang/rust#94476)
* On 2022-03-01, [8 - Make more use of `let_chains`](rust-lang/rust#94484)
* On 2022-03-01, [9 - Make more use of `let_chains`](rust-lang/rust#94498)
* On 2022-03-08, [Warn users about `||` in let chain expressions](rust-lang/rust#94754)
From the first RFC (2017-12-24) to the theoretical future stabilization day (2022-10-22), it can be said that this feature took 4 years, 9 months and 28 days of research, development, discussions, agreements and headaches to be settled.
## Divergent non-terminal matchers
More specifically, rust-lang/rust#86730.
```rust
macro_rules! mac {
($e:expr) => {
if $e {
true
} else {
false
}
};
}
fn main() {
// OK!
assert_eq!(mac!(true && let 1 = 1), true);
// ERROR! Anything starting with `let` is not considered an expression
assert_eq!(mac!(let 1 = 1 && true), true);
}
```
To the best of my knowledge, such error or divergence is orthogonal, does not prevent stabilization and can be tackled independently in the near future or effectively in the next Rust 2024 edition. If not, then https://github.com/c410-f3r/rust/tree/let-macro-blah contains a set of changes that will consider `let` an expression.
It is possible that none of the solutions above satisfies all applicable constraints but I personally don't know of any other plausible answers.
## Alternative syntax
Taking into account the usefulness of this feature and the overwhelming desire to use both now and in the past, `let PAT = EXPR` will be utilized for stabilization but it doesn't or shall create any obstacle for a **possible** future addition of `EXPR is PAT`.
The introductory snippet would then be written as the following.
```rust
if first_flower is Flower::Rose
&& first_flower_color is Color::Red
&& second_flower is Flower::Violet
&& second_flower_color is Color::Blue
&& pick_up_lines is &[first_pick_up_line, ..]
{
println!("Roses are red, violets are blue, {}", first_pick_up_line);
}
```
Just to reinforce, this PR only unblocks a **possible** future road for `EXPR is PAT` and does emphasize what is better or what is worse.
## Tests
* [Verifies the drop order of let chains and ensures it won't change in the future in an unpredictable way](https://github.com/rust-lang/rust/blob/master/src/test/ui/mir/mir_let_chains_drop_order.rs)
* [AST lowering does not wrap let chains in an `DropTemps` expression](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/ast-lowering-does-not-wrap-let-chains.rs)
* [Checks pretty printing output](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/ast-pretty-check.rs)
* [Verifies uninitialized variables due to MIR modifications](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/chains-without-let.rs)
* [A collection of statements where `let` expressions are forbidden](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/disallowed-positions.rs)
* [All or at least most of the places where let chains are allowed](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/feature-gate.rs)
* [Ensures that irrefutable lets are allowed in let chains](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/irrefutable-lets.rs)
* [issue-88498.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-88498.rs), [issue-90722.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-90722.rs), [issue-92145.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-92145.rs) and [issue-93150.rs](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/issue-93150.rs) were bugs found by third parties and fixed overtime.
* [Indexing was triggering a ICE due to a wrongly constructed MIR graph](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/no-double-assigments.rs)
* [Protects the precedence of `&&` in relation to other things](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/protect-precedences.rs)
* [`let_chains`, as well as `if_let_guard`, has a valid MIR graph that evaluates conditional expressions correctly](https://github.com/rust-lang/rust/blob/master/src/test/ui/rfc-2497-if-let-chains/then-else-blocks.rs)
Most of the infra-structure used by let chains is also used by `if` expressions in stable compiler versions since rust-lang/rust#80357 and rust-lang/rust#88572. As a result, no bugs were found since the integration of rust-lang/rust#88642.
## Possible future work
* Let chains in match guards is implemented and working but stabilization is blocked by `if_let_guard`.
* The usage of `let_chains` with `let_else` is possible but not implemented. Regardless, one attempt was introduced and closed in rust-lang/rust#93437.
Thanks `@Centril` for creating the RFC and huge thanks (again) to `@matthewjasper` for all the reviews, mentoring and MIR implementations.
Fixes #53667
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Basically copied and paste #59288/rust-lang/rust-clippy#4080 with some modifications.
The vast majority of tests were fixed and now there are only a few remaining. Since I am still unable to figure out the missing pieces, any help with the following list is welcome.
typeckexception: Cheated on this one to make CI green.thenandelseseparately.assert!: Modified but not "wrong". Maybe can be a good thing?src/test/ui/point-to-type-err-cause-on-impl-trait-return.rshas weird errors: Not sure why this is happening.