Warn users about `||` in let chain expressions #94754

c410-f3r · 2022-03-08T22:28:47Z

Or more specifically, warn that || operators are forbidden.

This PR is simple so I guess anyone can review 🤷

cc #53667
cc @matthewjasper

rust-highfive · 2022-03-08T22:28:50Z

r? @lcnr

(rust-highfive has picked a reviewer for you, use r? to override)

compiler/rustc_ast_passes/src/lib.rs

lcnr

one potential improvement, if you don't think that change is worth it, r=me

compiler/rustc_ast_passes/src/ast_validation.rs

lcnr · 2022-03-09T12:23:07Z

@bors delegate+

bors · 2022-03-09T12:23:09Z

✌️ @c410-f3r can now approve this pull request

c410-f3r · 2022-03-09T16:30:52Z

Thank you @lcnr

The code was modified according to your suggestion

@bors r=lcnr

bors · 2022-03-09T16:30:53Z

📌 Commit c7a5ad0 has been approved by lcnr

Warn users about `||` in let chain expressions Or more specifically, warn that `||` operators are forbidden. This PR is simple so I guess anyone can review 🤷 cc rust-lang#53667 cc `@matthewjasper`

lcnr · 2022-03-09T17:13:47Z

@bors r-

lcnr · 2022-03-09T17:14:44Z

compiler/rustc_ast_passes/src/ast_validation.rs

    }

    /// Emits an error banning the `let` expression provided in the given location.
-    fn ban_let_expr(&self, expr: &'a Expr) {
+    fn ban_let_expr(&self, expr: &'a Expr, or_span: Option<Span>) {


a part of why i suggested this change is that it allows us to do

Suggested change

fn ban_let_expr(&self, expr: &'a Expr, or_span: Option<Span>) {

fn ban_let_expr(&self, expr: &'a Expr, reason: ForbiddenListReason) {

lcnr · 2022-03-09T17:17:19Z

if this gets merged as part of #94774 that's also fine, that change can then be done in a follow up pr

lcnr · 2022-03-09T18:23:47Z

@bors r+ rollup

let's see whether this gets merged without the last commit

bors · 2022-03-09T18:23:48Z

📌 Commit 915f9a5 has been approved by lcnr

Warn users about `||` in let chain expressions Or more specifically, warn that `||` operators are forbidden. This PR is simple so I guess anyone can review 🤷 cc rust-lang#53667 cc `@matthewjasper`

…askrgr Rollup of 8 pull requests Successful merges: - rust-lang#91804 (Make some `Clone` impls `const`) - rust-lang#92541 (Mention intent of `From` trait in its docs) - rust-lang#93057 (Add Iterator::collect_into) - rust-lang#94739 (Suggest `if let`/`let_else` for refutable pat in `let`) - rust-lang#94754 (Warn users about `||` in let chain expressions) - rust-lang#94763 (Add documentation about lifetimes to thread::scope.) - rust-lang#94768 (Ignore `close_read_wakes_up` test on SGX platform) - rust-lang#94772 (Add miri to the well known conditional compilation names and values) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup

…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

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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Rollup of 7 pull requests #94774

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Warn users about || in let chain expressions

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Rollup of 16 pull requests #94784

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Rollup of 8 pull requests #94787

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Stabilize let_chains in Rust 1.64 #94927

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Second (control) mempool implementation nimiq/core-rs-albatross#885

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Tracking issue for eRFC 2497, "if- and while-let-chains, take 2" #53667

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Warn users about `||` in let chain expressions #94754

Warn users about `||` in let chain expressions #94754

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	fn ban_let_expr(&self, expr: &'a Expr, or_span: Option<Span>) {
	fn ban_let_expr(&self, expr: &'a Expr, reason: ForbiddenListReason) {

Warn users about || in let chain expressions #94754

Warn users about || in let chain expressions #94754

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Warn users about `||` in let chain expressions #94754

Warn users about `||` in let chain expressions #94754