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Auto merge of rust-lang#101318 - GuillaumeGomez:rollup-qsr51z4, r=Gui…
…llaumeGomez Rollup of 9 pull requests Successful merges: - rust-lang#97739 (Uplift the `let_underscore` lints from clippy into rustc.) - rust-lang#99583 (Add additional methods to the Demand type) - rust-lang#100147 (optimization of access level table construction) - rust-lang#100552 (rustc_target: Add a compatibility layer to separate internal and user-facing linker flavors) - rust-lang#100827 (Simplify MIR opt tests) - rust-lang#101166 (Generate error index with mdbook instead of raw HTML pages) - rust-lang#101294 (Fix rust-lang#100844 rebase accident) - rust-lang#101298 (rustdoc: remove unused CSS `#main-content > .since`) - rust-lang#101304 (Add autolabels for `A-query-system`) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,175 @@ | ||
| use crate::{LateContext, LateLintPass, LintContext}; | ||
| use rustc_errors::{Applicability, LintDiagnosticBuilder, MultiSpan}; | ||
| use rustc_hir as hir; | ||
| use rustc_middle::ty; | ||
| use rustc_span::Symbol; | ||
|
|
||
| declare_lint! { | ||
| /// The `let_underscore_drop` lint checks for statements which don't bind | ||
| /// an expression which has a non-trivial Drop implementation to anything, | ||
| /// causing the expression to be dropped immediately instead of at end of | ||
| /// scope. | ||
| /// | ||
| /// ### Example | ||
| /// ``` | ||
| /// struct SomeStruct; | ||
| /// impl Drop for SomeStruct { | ||
| /// fn drop(&mut self) { | ||
| /// println!("Dropping SomeStruct"); | ||
| /// } | ||
| /// } | ||
| /// | ||
| /// fn main() { | ||
| /// #[warn(let_underscore_drop)] | ||
| /// // SomeStuct is dropped immediately instead of at end of scope, | ||
| /// // so "Dropping SomeStruct" is printed before "end of main". | ||
| /// // The order of prints would be reversed if SomeStruct was bound to | ||
| /// // a name (such as "_foo"). | ||
| /// let _ = SomeStruct; | ||
| /// println!("end of main"); | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// {{produces}} | ||
| /// | ||
| /// ### Explanation | ||
| /// | ||
| /// Statements which assign an expression to an underscore causes the | ||
| /// expression to immediately drop instead of extending the expression's | ||
| /// lifetime to the end of the scope. This is usually unintended, | ||
| /// especially for types like `MutexGuard`, which are typically used to | ||
| /// lock a mutex for the duration of an entire scope. | ||
| /// | ||
| /// If you want to extend the expression's lifetime to the end of the scope, | ||
| /// assign an underscore-prefixed name (such as `_foo`) to the expression. | ||
| /// If you do actually want to drop the expression immediately, then | ||
| /// calling `std::mem::drop` on the expression is clearer and helps convey | ||
| /// intent. | ||
| pub LET_UNDERSCORE_DROP, | ||
| Allow, | ||
| "non-binding let on a type that implements `Drop`" | ||
| } | ||
|
|
||
| declare_lint! { | ||
| /// The `let_underscore_lock` lint checks for statements which don't bind | ||
| /// a mutex to anything, causing the lock to be released immediately instead | ||
| /// of at end of scope, which is typically incorrect. | ||
| /// | ||
| /// ### Example | ||
| /// ```compile_fail | ||
| /// use std::sync::{Arc, Mutex}; | ||
| /// use std::thread; | ||
| /// let data = Arc::new(Mutex::new(0)); | ||
| /// | ||
| /// thread::spawn(move || { | ||
| /// // The lock is immediately released instead of at the end of the | ||
| /// // scope, which is probably not intended. | ||
| /// let _ = data.lock().unwrap(); | ||
| /// println!("doing some work"); | ||
| /// let mut lock = data.lock().unwrap(); | ||
| /// *lock += 1; | ||
| /// }); | ||
| /// ``` | ||
| /// | ||
| /// {{produces}} | ||
| /// | ||
| /// ### Explanation | ||
| /// | ||
| /// Statements which assign an expression to an underscore causes the | ||
| /// expression to immediately drop instead of extending the expression's | ||
| /// lifetime to the end of the scope. This is usually unintended, | ||
| /// especially for types like `MutexGuard`, which are typically used to | ||
| /// lock a mutex for the duration of an entire scope. | ||
| /// | ||
| /// If you want to extend the expression's lifetime to the end of the scope, | ||
| /// assign an underscore-prefixed name (such as `_foo`) to the expression. | ||
| /// If you do actually want to drop the expression immediately, then | ||
| /// calling `std::mem::drop` on the expression is clearer and helps convey | ||
| /// intent. | ||
| pub LET_UNDERSCORE_LOCK, | ||
| Deny, | ||
| "non-binding let on a synchronization lock" | ||
| } | ||
|
|
||
| declare_lint_pass!(LetUnderscore => [LET_UNDERSCORE_DROP, LET_UNDERSCORE_LOCK]); | ||
|
|
||
| const SYNC_GUARD_SYMBOLS: [Symbol; 3] = [ | ||
| rustc_span::sym::MutexGuard, | ||
| rustc_span::sym::RwLockReadGuard, | ||
| rustc_span::sym::RwLockWriteGuard, | ||
| ]; | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for LetUnderscore { | ||
| fn check_local(&mut self, cx: &LateContext<'_>, local: &hir::Local<'_>) { | ||
| if !matches!(local.pat.kind, hir::PatKind::Wild) { | ||
| return; | ||
| } | ||
| if let Some(init) = local.init { | ||
| let init_ty = cx.typeck_results().expr_ty(init); | ||
| // If the type has a trivial Drop implementation, then it doesn't | ||
| // matter that we drop the value immediately. | ||
| if !init_ty.needs_drop(cx.tcx, cx.param_env) { | ||
| return; | ||
| } | ||
| let is_sync_lock = match init_ty.kind() { | ||
| ty::Adt(adt, _) => SYNC_GUARD_SYMBOLS | ||
| .iter() | ||
| .any(|guard_symbol| cx.tcx.is_diagnostic_item(*guard_symbol, adt.did())), | ||
| _ => false, | ||
| }; | ||
|
|
||
| if is_sync_lock { | ||
| let mut span = MultiSpan::from_spans(vec![local.pat.span, init.span]); | ||
| span.push_span_label( | ||
| local.pat.span, | ||
| "this lock is not assigned to a binding and is immediately dropped".to_string(), | ||
| ); | ||
| span.push_span_label( | ||
| init.span, | ||
| "this binding will immediately drop the value assigned to it".to_string(), | ||
| ); | ||
| cx.struct_span_lint(LET_UNDERSCORE_LOCK, span, |lint| { | ||
| build_and_emit_lint( | ||
| lint, | ||
| local, | ||
| init.span, | ||
| "non-binding let on a synchronization lock", | ||
| ) | ||
| }) | ||
| } else { | ||
| cx.struct_span_lint(LET_UNDERSCORE_DROP, local.span, |lint| { | ||
| build_and_emit_lint( | ||
| lint, | ||
| local, | ||
| init.span, | ||
| "non-binding let on a type that implements `Drop`", | ||
| ); | ||
| }) | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| fn build_and_emit_lint( | ||
| lint: LintDiagnosticBuilder<'_, ()>, | ||
| local: &hir::Local<'_>, | ||
| init_span: rustc_span::Span, | ||
| msg: &str, | ||
| ) { | ||
| lint.build(msg) | ||
| .span_suggestion_verbose( | ||
| local.pat.span, | ||
| "consider binding to an unused variable to avoid immediately dropping the value", | ||
| "_unused", | ||
| Applicability::MachineApplicable, | ||
| ) | ||
| .multipart_suggestion( | ||
| "consider immediately dropping the value", | ||
| vec![ | ||
| (local.span.until(init_span), "drop(".to_string()), | ||
| (init_span.shrink_to_hi(), ")".to_string()), | ||
| ], | ||
| Applicability::MachineApplicable, | ||
| ) | ||
| .emit(); | ||
| } |
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