Add match guard let chain drop order and scoping tests #140981
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based on tests/ui/rfcs/rfc-2497-if-let-chains/temporary-early-drop.rs
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…iaskrgr Rollup of 6 pull requests Successful merges: - rust-lang#140981 (Add match guard let chain drop order and scoping tests) - rust-lang#141042 (ci: split powerpc64le-linux job) - rust-lang#141078 (ci: split dist-arm-linux job) - rust-lang#141222 (Implement `ptr::try_cast_aligned` and `NonNull::try_cast_aligned`.) - rust-lang#141308 (Do not call name() on rpitit assoc_item) - rust-lang#141316 (Update books) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#140981 - est31:guard_let_chains_tests, r=petrochenkov Add match guard let chain drop order and scoping tests We have a bunch of tests for if let chain drop order, but those tests don't cover match guard chains to the same depth. This PR adds the following tests: * match guard equivalents of the if let chains tests in the `drop-order-comparisons.rs` test, added by rust-lang#133605. * match guard equivalent of the `mir_let_chains_drop_order.rs` test, added by rust-lang#107251 * match guard equivalent of `temporary-early-drop.rs`, added by rust-lang#133093 The added tests all have variants for 2021 and 2024, showing that the behavior on both editions matches that of if let chains on 2024. tracking issue: rust-lang#51114
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…31,fee1-dead Stabilize `if let` guards (`feature(if_let_guard)`) ## Summary This proposes the stabilization of `if let` guards (tracking issue: rust-lang#51114, RFC: rust-lang/rfcs#2294). This feature allows `if let` expressions to be used directly within match arm guards, enabling conditional pattern matching within guard clauses. ## What is being stabilized The ability to use `if let` expressions within match arm guards. Example: ```rust enum Command { Run(String), Stop, Pause, } fn process_command(cmd: Command, state: &mut String) { match cmd { Command::Run(name) if let Some(first_char) = name.chars().next() && first_char.is_ascii_alphabetic() => { // Both `name` and `first_char` are available here println!("Running command: {} (starts with '{}')", name, first_char); state.push_str(&format!("Running {}", name)); } Command::Run(name) => { println!("Cannot run command '{}'. Invalid name.", name); } Command::Stop if state.contains("running") => { println!("Stopping current process."); state.clear(); } _ => { println!("Unhandled command or state."); } } } ``` ## Motivation The primary motivation for `if let` guards is to reduce nesting and improve readability when conditional logic depends on pattern matching. Without this feature, such logic requires nested `if let` statements within match arms: ```rust // Without if let guards match value { Some(x) => { if let Ok(y) = compute(x) { // Both `x` and `y` are available here println!("{}, {}", x, y); } } _ => {} } // With if let guards match value { Some(x) if let Ok(y) = compute(x) => { // Both `x` and `y` are available here println!("{}, {}", x, y); } _ => {} } ``` ## Implementation and Testing The feature has been implemented and tested comprehensively across different scenarios: ### Core Functionality Tests **Scoping and variable binding:** - [`scope.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/scope.rs) - Verifies that bindings created in `if let` guards are properly scoped and available in match arms - [`shadowing.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/shadowing.rs) - Tests that variable shadowing works correctly within guards - [`scoping-consistency.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/scoping-consistency.rs) - Ensures temporaries in guards remain valid for the duration of their match arms **Type system integration:** - [`type-inference.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/type-inference.rs) - Confirms type inference works correctly in `if let` guards - [`typeck.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/typeck.rs) - Verifies type mismatches are caught appropriately **Pattern matching semantics:** - [`exhaustive.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/exhaustive.rs) - Validates that `if let` guards are correctly handled in exhaustiveness analysis - [`move-guard-if-let.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/move-guard-if-let.rs) and [`move-guard-if-let-chain.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/move-guard-if-let-chain.rs) - Test that conditional moves in guards are tracked correctly by the borrow checker ### Error Handling and Diagnostics - [`warns.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/warns.rs) - Tests warnings for irrefutable patterns and unreachable code in guards - [`parens.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/parens.rs) - Ensures parentheses around `let` expressions are properly rejected - [`macro-expanded.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/macro-expanded.rs) - Verifies macro expansions that produce invalid constructs are caught - [`guard-mutability-2.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/guard-mutability-2.rs) - Tests mutability and ownership violations in guards - [`ast-validate-guards.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2497-if-let-chains/ast-validate-guards.rs) - Validates AST-level syntax restrictions ### Drop Order and Temporaries **Key insight:** Unlike `let_chains` in regular `if` expressions, `if let` guards do not have drop order inconsistencies because: 1. Match guards are clearly scoped to their arms 2. There is no "else block" equivalent that could cause temporal confusion - [`drop-order.rs`](https://github.com/rust-lang/rust/blob/5796073c134eaac30475f9a19462c4e716c9119c/tests/ui/rfcs/rfc-2294-if-let-guard/drop-order.rs) - Tests that temporaries in guards are dropped at the correct time - [`compare-drop-order.rs`](https://github.com/rust-lang/rust/blob/aef3f5fdf052fbbc16e174aef5da6d50832ca316/tests/ui/rfcs/rfc-2294-if-let-guard/compare-drop-order.rs) - Compares drop order between `if let` guards and nested `if let` in match arms, confirming they behave identically across all editions - rust-lang#140981 - A complicated drop order test involved `let chain` was made by `@est31` ## Edition Compatibility This feature stabilizes on **all editions**, unlike `let_chains` which was limited to edition 2024. This is safe because: 1. `if let` guards don't suffer from the drop order issues that affected `let_chains` in regular `if` expressions 2. The scoping is unambiguous - guards are clearly tied to their match arms 3. Extensive testing confirms identical behavior across all editions ## Interactions with Future Features The lang team has reviewed potential interactions with planned "guard patterns" and determined that stabilizing `if let` guards now does not create obstacles for future work. The scoping and evaluation semantics established here align with what guard patterns will need. ## Unresolved Issues All blocking issues have been resolved: - [x] - rust-lang#140981 - [x] - added tests description by `@jieyouxu` request - [x] - Concers from `@scottmcm` about stabilizing this across all editions - [x] - check if drop order in all edition when using `let chains` inside `if let` guard is the same - [x] - interactions with guard patters --- **Related:** - Tracking Issue: rust-lang#51114 - RFC: rust-lang/rfcs#2294 - Documentation PR: rust-lang/reference#1823
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We have a bunch of tests for if let chain drop order, but those tests don't cover match guard chains to the same depth. This PR adds the following tests:
drop-order-comparisons.rstest, added by Add extensive set of drop order tests #133605.mir_let_chains_drop_order.rstest, added by Rescope temp lifetime in if-let into IfElse with migration lint #107251temporary-early-drop.rs, added by Let chains tests #133093The added tests all have variants for 2021 and 2024, showing that the behavior on both editions matches that of if let chains on 2024.
tracking issue: #51114