From 6641f9f6e138a3166b06fc27d62e7c349e1f927d Mon Sep 17 00:00:00 2001 From: Ruihan Li Date: Sat, 27 Apr 2024 23:47:11 +0800 Subject: [PATCH] Track lifetime on values with significant drop --- .../matches/significant_drop_in_scrutinee.rs | 420 ++++++++++-------- tests/ui/significant_drop_in_scrutinee.rs | 98 +++- tests/ui/significant_drop_in_scrutinee.stderr | 220 ++++----- 3 files changed, 434 insertions(+), 304 deletions(-) diff --git a/clippy_lints/src/matches/significant_drop_in_scrutinee.rs b/clippy_lints/src/matches/significant_drop_in_scrutinee.rs index 6ac0705abb2..2f72e59834f 100644 --- a/clippy_lints/src/matches/significant_drop_in_scrutinee.rs +++ b/clippy_lints/src/matches/significant_drop_in_scrutinee.rs @@ -1,12 +1,17 @@ +use std::ops::ControlFlow; + use crate::FxHashSet; use clippy_utils::diagnostics::span_lint_and_then; use clippy_utils::source::{indent_of, snippet}; +use clippy_utils::ty::{for_each_top_level_late_bound_region, is_copy}; use clippy_utils::{get_attr, is_lint_allowed}; +use itertools::Itertools; +use rustc_ast::Mutability; use rustc_errors::{Applicability, Diag}; use rustc_hir::intravisit::{walk_expr, Visitor}; use rustc_hir::{Arm, Expr, ExprKind, MatchSource}; use rustc_lint::{LateContext, LintContext}; -use rustc_middle::ty::{GenericArgKind, Ty}; +use rustc_middle::ty::{GenericArgKind, Region, RegionKind, Ty, TyCtxt, TypeVisitable, TypeVisitor}; use rustc_span::Span; use super::SIGNIFICANT_DROP_IN_SCRUTINEE; @@ -22,43 +27,34 @@ pub(super) fn check<'tcx>( return; } - if let Some((suggestions, message)) = has_significant_drop_in_scrutinee(cx, scrutinee, source) { - for found in suggestions { - span_lint_and_then(cx, SIGNIFICANT_DROP_IN_SCRUTINEE, found.found_span, message, |diag| { - set_diagnostic(diag, cx, expr, found); - let s = Span::new(expr.span.hi(), expr.span.hi(), expr.span.ctxt(), None); - diag.span_label(s, "temporary lives until here"); - for span in has_significant_drop_in_arms(cx, arms) { - diag.span_label(span, "another value with significant `Drop` created here"); - } - diag.note("this might lead to deadlocks or other unexpected behavior"); - }); - } + let (suggestions, message) = has_significant_drop_in_scrutinee(cx, scrutinee, source); + for found in suggestions { + span_lint_and_then(cx, SIGNIFICANT_DROP_IN_SCRUTINEE, found.found_span, message, |diag| { + set_diagnostic(diag, cx, expr, found); + let s = Span::new(expr.span.hi(), expr.span.hi(), expr.span.ctxt(), None); + diag.span_label(s, "temporary lives until here"); + for span in has_significant_drop_in_arms(cx, arms) { + diag.span_label(span, "another value with significant `Drop` created here"); + } + diag.note("this might lead to deadlocks or other unexpected behavior"); + }); } } fn set_diagnostic<'tcx>(diag: &mut Diag<'_, ()>, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, found: FoundSigDrop) { - if found.lint_suggestion == LintSuggestion::MoveAndClone { - // If our suggestion is to move and clone, then we want to leave it to the user to - // decide how to address this lint, since it may be that cloning is inappropriate. - // Therefore, we won't to emit a suggestion. - return; - } - let original = snippet(cx, found.found_span, ".."); let trailing_indent = " ".repeat(indent_of(cx, found.found_span).unwrap_or(0)); - let replacement = if found.lint_suggestion == LintSuggestion::MoveAndDerefToCopy { - format!("let value = *{original};\n{trailing_indent}") - } else if found.is_unit_return_val { - // If the return value of the expression to be moved is unit, then we don't need to - // capture the result in a temporary -- we can just replace it completely with `()`. - format!("{original};\n{trailing_indent}") - } else { - format!("let value = {original};\n{trailing_indent}") + let replacement = { + let (def_part, deref_part) = if found.is_unit_return_val { + ("", String::new()) + } else { + ("let value = ", "*".repeat(found.peel_ref_times)) + }; + format!("{def_part}{deref_part}{original};\n{trailing_indent}") }; - let suggestion_message = if found.lint_suggestion == LintSuggestion::MoveOnly { + let suggestion_message = if found.peel_ref_times == 0 { "try moving the temporary above the match" } else { "try moving the temporary above the match and create a copy" @@ -66,8 +62,11 @@ fn set_diagnostic<'tcx>(diag: &mut Diag<'_, ()>, cx: &LateContext<'tcx>, expr: & let scrutinee_replacement = if found.is_unit_return_val { "()".to_owned() - } else { + } else if found.peel_ref_times == 0 { "value".to_owned() + } else { + let ref_part = "&".repeat(found.peel_ref_times); + format!("({ref_part}value)") }; diag.multipart_suggestion( @@ -86,20 +85,18 @@ fn has_significant_drop_in_scrutinee<'tcx>( cx: &LateContext<'tcx>, scrutinee: &'tcx Expr<'tcx>, source: MatchSource, -) -> Option<(Vec, &'static str)> { +) -> (Vec, &'static str) { let mut helper = SigDropHelper::new(cx); let scrutinee = match (source, &scrutinee.kind) { (MatchSource::ForLoopDesugar, ExprKind::Call(_, [e])) => e, _ => scrutinee, }; - helper.find_sig_drop(scrutinee).map(|drops| { - let message = if source == MatchSource::Normal { - "temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression" - } else { - "temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression" - }; - (drops, message) - }) + let message = if source == MatchSource::Normal { + "temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression" + } else { + "temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression" + }; + (helper.find_sig_drop(scrutinee), message) } struct SigDropChecker<'a, 'tcx> { @@ -172,205 +169,248 @@ fn has_sig_drop_attr_impl(&mut self, ty: Ty<'tcx>) -> bool { } } +#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)] +enum SigDropHolder { + /// No values with significant drop present in this expression. + /// + /// Expressions that we've emited lints do not count. + None, + /// Some field in this expression references to values with significant drop. + /// + /// Example: `(1, &data.lock().field)`. + PackedRef, + /// The value of this expression references to values with significant drop. + /// + /// Example: `data.lock().field`. + DirectRef, + /// This expression should be moved out to avoid significant drop in scrutinee. + Moved, +} + +impl Default for SigDropHolder { + fn default() -> Self { + Self::None + } +} + struct SigDropHelper<'a, 'tcx> { cx: &'a LateContext<'tcx>, - is_chain_end: bool, - has_significant_drop: bool, - current_sig_drop: Option, - sig_drop_spans: Option>, - special_handling_for_binary_op: bool, + parent_expr: Option<&'tcx Expr<'tcx>>, + sig_drop_holder: SigDropHolder, + sig_drop_spans: Vec, sig_drop_checker: SigDropChecker<'a, 'tcx>, } -#[expect(clippy::enum_variant_names)] -#[derive(Debug, PartialEq, Eq, Clone, Copy)] -enum LintSuggestion { - MoveOnly, - MoveAndDerefToCopy, - MoveAndClone, -} - -#[derive(Clone, Copy)] +#[derive(Clone, Copy, Debug)] struct FoundSigDrop { found_span: Span, is_unit_return_val: bool, - lint_suggestion: LintSuggestion, + peel_ref_times: usize, } impl<'a, 'tcx> SigDropHelper<'a, 'tcx> { fn new(cx: &'a LateContext<'tcx>) -> SigDropHelper<'a, 'tcx> { SigDropHelper { cx, - is_chain_end: true, - has_significant_drop: false, - current_sig_drop: None, - sig_drop_spans: None, - special_handling_for_binary_op: false, + parent_expr: None, + sig_drop_holder: SigDropHolder::None, + sig_drop_spans: Vec::new(), sig_drop_checker: SigDropChecker::new(cx), } } - fn find_sig_drop(&mut self, match_expr: &'tcx Expr<'_>) -> Option> { + fn find_sig_drop(&mut self, match_expr: &'tcx Expr<'_>) -> Vec { self.visit_expr(match_expr); - // If sig drop spans is empty but we found a significant drop, it means that we didn't find - // a type that was trivially copyable as we moved up the chain after finding a significant - // drop, so move the entire scrutinee. - if self.has_significant_drop && self.sig_drop_spans.is_none() { - self.try_setting_current_suggestion(match_expr, true); - self.move_current_suggestion(); - } - - self.sig_drop_spans.take() + core::mem::take(&mut self.sig_drop_spans) } - fn replace_current_sig_drop( - &mut self, - found_span: Span, - is_unit_return_val: bool, - lint_suggestion: LintSuggestion, - ) { - self.current_sig_drop.replace(FoundSigDrop { + fn replace_current_sig_drop(&mut self, found_span: Span, is_unit_return_val: bool, peel_ref_times: usize) { + self.sig_drop_spans.clear(); + self.sig_drop_spans.push(FoundSigDrop { found_span, is_unit_return_val, - lint_suggestion, + peel_ref_times, }); } - /// This will try to set the current suggestion (so it can be moved into the suggestions vec - /// later). If `allow_move_and_clone` is false, the suggestion *won't* be set -- this gives us - /// an opportunity to look for another type in the chain that will be trivially copyable. - /// However, if we are at the end of the chain, we want to accept whatever is there. (The - /// suggestion won't actually be output, but the diagnostic message will be output, so the user - /// can determine the best way to handle the lint.) - fn try_setting_current_suggestion(&mut self, expr: &'tcx Expr<'_>, allow_move_and_clone: bool) { - if self.current_sig_drop.is_some() { - return; + fn try_move_sig_drop(&mut self, expr: &'tcx Expr<'_>, parent_expr: &'tcx Expr<'_>) { + if self.sig_drop_holder == SigDropHolder::Moved { + self.sig_drop_holder = SigDropHolder::None; } - let ty = self.cx.typeck_results().expr_ty(expr); - if ty.is_ref() { - // We checked that the type was ref, so builtin_deref will return Some, - // but let's avoid any chance of an ICE. - if let Some(ty) = ty.builtin_deref(true) { - if ty.is_trivially_pure_clone_copy() { - self.replace_current_sig_drop(expr.span, false, LintSuggestion::MoveAndDerefToCopy); - } else if allow_move_and_clone { - self.replace_current_sig_drop(expr.span, false, LintSuggestion::MoveAndClone); - } + + if self.sig_drop_holder == SigDropHolder::DirectRef { + self.sig_drop_holder = SigDropHolder::PackedRef; + self.try_move_sig_drop_direct_ref(expr, parent_expr); + } else if self.sig_drop_checker.is_sig_drop_expr(expr) { + // The values with significant drop can be moved to some other functions. For example, consider + // `drop(data.lock())`. We use `SigDropHolder::None` here to avoid emitting lints in such scenarios. + self.sig_drop_holder = SigDropHolder::None; + self.try_move_sig_drop_direct_ref(expr, parent_expr); + } + + if self.sig_drop_holder != SigDropHolder::None { + let parent_ty = self.cx.typeck_results().expr_ty(parent_expr); + if !ty_has_erased_regions(parent_ty) && !parent_expr.is_syntactic_place_expr() { + self.replace_current_sig_drop(parent_expr.span, parent_ty.is_unit(), 0); + self.sig_drop_holder = SigDropHolder::Moved; + } + + let (peel_ref_ty, peel_ref_times) = ty_peel_refs(parent_ty); + if !ty_has_erased_regions(peel_ref_ty) && is_copy(self.cx, peel_ref_ty) { + self.replace_current_sig_drop(parent_expr.span, peel_ref_ty.is_unit(), peel_ref_times); + self.sig_drop_holder = SigDropHolder::Moved; } - } else if ty.is_trivially_pure_clone_copy() { - self.replace_current_sig_drop(expr.span, false, LintSuggestion::MoveOnly); - } else if allow_move_and_clone { - self.replace_current_sig_drop(expr.span, false, LintSuggestion::MoveAndClone); } } - fn move_current_suggestion(&mut self) { - if let Some(current) = self.current_sig_drop.take() { - self.sig_drop_spans.get_or_insert_with(Vec::new).push(current); + fn try_move_sig_drop_direct_ref(&mut self, expr: &'tcx Expr<'_>, parent_expr: &'tcx Expr<'_>) { + let arg_idx = match parent_expr.kind { + ExprKind::MethodCall(_, receiver, exprs, _) => std::iter::once(receiver) + .chain(exprs.iter()) + .find_position(|ex| ex.hir_id == expr.hir_id) + .map(|(idx, _)| idx), + ExprKind::Call(_, exprs) => exprs + .iter() + .find_position(|ex| ex.hir_id == expr.hir_id) + .map(|(idx, _)| idx), + ExprKind::Binary(_, lhs, rhs) | ExprKind::AssignOp(_, lhs, rhs) => [lhs, rhs] + .iter() + .find_position(|ex| ex.hir_id == expr.hir_id) + .map(|(idx, _)| idx), + ExprKind::Unary(_, ex) => (ex.hir_id == expr.hir_id).then_some(0), + _ => { + // Here we assume that all other expressions create or propagate the reference to the value with + // significant drop. + self.sig_drop_holder = SigDropHolder::DirectRef; + return; + }, + }; + let Some(arg_idx) = arg_idx else { + return; + }; + + let fn_sig = if let Some(def_id) = self.cx.typeck_results().type_dependent_def_id(parent_expr.hir_id) { + self.cx.tcx.fn_sig(def_id).instantiate_identity() + } else { + return; + }; + + let input_re = if let Some(input_ty) = fn_sig.skip_binder().inputs().get(arg_idx) + && let rustc_middle::ty::Ref(input_re, _, _) = input_ty.kind() + { + input_re + } else { + return; + }; + + // Late bound lifetime parameters are not related to any constraints, so we can track them in a very + // simple manner. For other lifetime parameters, we give up and update the state to `PackedRef`. + let RegionKind::ReBound(_, input_re_bound) = input_re.kind() else { + self.sig_drop_holder = SigDropHolder::PackedRef; + return; + }; + let contains_input_re = |re_bound| { + if re_bound == input_re_bound { + ControlFlow::Break(()) + } else { + ControlFlow::Continue(()) + } + }; + + let output_ty = fn_sig.skip_binder().output(); + if let rustc_middle::ty::Ref(output_re, peel_ref_ty, _) = output_ty.kind() + && input_re == output_re + && for_each_top_level_late_bound_region(*peel_ref_ty, contains_input_re).is_continue() + { + // We're lucky! The output type is still a direct reference to the value with significant drop. + self.sig_drop_holder = SigDropHolder::DirectRef; + } else if for_each_top_level_late_bound_region(output_ty, contains_input_re).is_continue() { + // The lifetime to the value with significant drop goes away. So we can emit a lint that suggests to + // move the expression out. + self.replace_current_sig_drop(parent_expr.span, output_ty.is_unit(), 0); + self.sig_drop_holder = SigDropHolder::Moved; + } else { + // TODO: The lifetime is still there but it's for a inner type. For instance, consider + // `Some(&mutex.lock().field)`, which has a type of `Option<&u32>`. How to address this scenario? + self.sig_drop_holder = SigDropHolder::PackedRef; + } + } +} + +fn ty_peel_refs(mut ty: Ty<'_>) -> (Ty<'_>, usize) { + let mut n = 0; + while let rustc_middle::ty::Ref(_, new_ty, Mutability::Not) = ty.kind() { + ty = *new_ty; + n += 1; + } + (ty, n) +} + +fn ty_has_erased_regions(ty: Ty<'_>) -> bool { + struct V; + + impl<'tcx> TypeVisitor> for V { + type Result = ControlFlow<()>; + + fn visit_region(&mut self, region: Region<'tcx>) -> Self::Result { + if region.is_erased() { + ControlFlow::Break(()) + } else { + ControlFlow::Continue(()) + } } } - fn visit_exprs_for_binary_ops( - &mut self, - left: &'tcx Expr<'_>, - right: &'tcx Expr<'_>, - is_unit_return_val: bool, - span: Span, - ) { - self.special_handling_for_binary_op = true; - self.visit_expr(left); - self.visit_expr(right); - - // If either side had a significant drop, suggest moving the entire scrutinee to avoid - // unnecessary copies and to simplify cases where both sides have significant drops. - if self.has_significant_drop { - self.replace_current_sig_drop(span, is_unit_return_val, LintSuggestion::MoveOnly); - } - - self.special_handling_for_binary_op = false; - } + ty.visit_with(&mut V).is_break() } impl<'a, 'tcx> Visitor<'tcx> for SigDropHelper<'a, 'tcx> { fn visit_expr(&mut self, ex: &'tcx Expr<'_>) { - if !self.is_chain_end && self.sig_drop_checker.is_sig_drop_expr(ex) { - self.has_significant_drop = true; + // We've emited a lint on some neighborhood expression. That lint will suggest to move out the + // _parent_ expression (not the expression itself). Since we decide to move out the parent + // expression, it is pointless to continue to process the current expression. + if self.sig_drop_holder == SigDropHolder::Moved { return; } - self.is_chain_end = false; + + // These states are of neighborhood expressions. We save and clear them here, and we'll later merge + // the states of the current expression with them at the end of the method. + let sig_drop_holder_before = core::mem::take(&mut self.sig_drop_holder); + let sig_drop_spans_before = core::mem::take(&mut self.sig_drop_spans); + let parent_expr_before = self.parent_expr.replace(ex); match ex.kind { - ExprKind::MethodCall(_, expr, ..) => { - self.visit_expr(expr); - } - ExprKind::Binary(_, left, right) => { - self.visit_exprs_for_binary_ops(left, right, false, ex.span); - } - ExprKind::Assign(left, right, _) | ExprKind::AssignOp(_, left, right) => { - self.visit_exprs_for_binary_ops(left, right, true, ex.span); - } - ExprKind::Tup(exprs) => { - for expr in exprs { - self.visit_expr(expr); - if self.has_significant_drop { - // We may have not have set current_sig_drop if all the suggestions were - // MoveAndClone, so add this tuple item's full expression in that case. - if self.current_sig_drop.is_none() { - self.try_setting_current_suggestion(expr, true); - } + // Skip blocks because values in blocks will be dropped as usual. + ExprKind::Block(..) => (), + _ => walk_expr(self, ex), + } - // Now we are guaranteed to have something, so add it to the final vec. - self.move_current_suggestion(); - } - // Reset `has_significant_drop` after each tuple expression so we can look for - // additional cases. - self.has_significant_drop = false; - } - if self.sig_drop_spans.is_some() { - self.has_significant_drop = true; - } - } - ExprKind::Array(..) | - ExprKind::Call(..) | - ExprKind::Unary(..) | - ExprKind::If(..) | - ExprKind::Match(..) | - ExprKind::Field(..) | - ExprKind::Index(..) | - ExprKind::Ret(..) | - ExprKind::Become(..) | - ExprKind::Repeat(..) | - ExprKind::Yield(..) => walk_expr(self, ex), - ExprKind::AddrOf(_, _, _) | - ExprKind::Block(_, _) | - ExprKind::Break(_, _) | - ExprKind::Cast(_, _) | - // Don't want to check the closure itself, only invocation, which is covered by MethodCall - ExprKind::Closure { .. } | - ExprKind::ConstBlock(_) | - ExprKind::Continue(_) | - ExprKind::DropTemps(_) | - ExprKind::Err(_) | - ExprKind::InlineAsm(_) | - ExprKind::OffsetOf(_, _) | - ExprKind::Let(_) | - ExprKind::Lit(_) | - ExprKind::Loop(_, _, _, _) | - ExprKind::Path(_) | - ExprKind::Struct(_, _, _) | - ExprKind::Type(_, _) => { - return; + if let Some(parent_ex) = parent_expr_before { + match parent_ex.kind { + ExprKind::Assign(lhs, _, _) | ExprKind::AssignOp(_, lhs, _) + if lhs.hir_id == ex.hir_id && self.sig_drop_holder == SigDropHolder::Moved => + { + // Never move out only the assignee. Instead, we should always move out the whole assigment. + self.replace_current_sig_drop(parent_ex.span, true, 0); + }, + _ => { + self.try_move_sig_drop(ex, parent_ex); + }, } } - // Once a significant temporary has been found, we need to go back up at least 1 level to - // find the span to extract for replacement, so the temporary gets dropped. However, for - // binary ops, we want to move the whole scrutinee so we avoid unnecessary copies and to - // simplify cases where both sides have significant drops. - if self.has_significant_drop && !self.special_handling_for_binary_op { - self.try_setting_current_suggestion(ex, false); + self.sig_drop_holder = std::cmp::max(self.sig_drop_holder, sig_drop_holder_before); + + // We do not need those old spans in neighborhood expressions if we emit a lint that suggests to + // move out the _parent_ expression (i.e., `self.sig_drop_holder == SigDropHolder::Moved`). + if self.sig_drop_holder != SigDropHolder::Moved { + let mut sig_drop_spans = sig_drop_spans_before; + sig_drop_spans.append(&mut self.sig_drop_spans); + self.sig_drop_spans = sig_drop_spans; } + + self.parent_expr = parent_expr_before; } } diff --git a/tests/ui/significant_drop_in_scrutinee.rs b/tests/ui/significant_drop_in_scrutinee.rs index 7fc89bb9538..8ee15440ccf 100644 --- a/tests/ui/significant_drop_in_scrutinee.rs +++ b/tests/ui/significant_drop_in_scrutinee.rs @@ -274,11 +274,20 @@ fn should_trigger_lint_for_tuple_in_scrutinee() { }, (_, _, _) => {}, }; + } +} +// Should not trigger lint since `String::as_str` returns a reference (i.e., `&str`) +// to the locked data (i.e., the `String`) and it is not surprising that matching such +// a reference needs to keep the data locked until the end of the match block. +fn should_not_trigger_lint_for_string_as_str() { + let mutex1 = Mutex::new(StateWithField { s: "one".to_owned() }); + + { + let mutex2 = Mutex::new(StateWithField { s: "two".to_owned() }); let mutex3 = Mutex::new(StateWithField { s: "three".to_owned() }); + match mutex3.lock().unwrap().s.as_str() { - //~^ ERROR: temporary with significant `Drop` in `match` scrutinee will live until - //~| NOTE: this might lead to deadlocks or other unexpected behavior "three" => { println!("started"); mutex1.lock().unwrap().s.len(); @@ -289,8 +298,6 @@ fn should_trigger_lint_for_tuple_in_scrutinee() { }; match (true, mutex3.lock().unwrap().s.as_str()) { - //~^ ERROR: temporary with significant `Drop` in `match` scrutinee will live until - //~| NOTE: this might lead to deadlocks or other unexpected behavior (_, "three") => { println!("started"); mutex1.lock().unwrap().s.len(); @@ -514,16 +521,15 @@ fn lock(&self) -> Box> { } } -fn should_trigger_lint_for_boxed_mutex_guard_holding_string() { +fn should_not_trigger_lint_for_string_ref() { let s = StateStringWithBoxedMutexGuard::new(); let matcher = String::from("A String"); - // Should trigger lint because a temporary Box holding a type with a significant drop in a match - // scrutinee may have a potentially surprising lifetime. + // Should not trigger lint because the second `deref` returns a string reference (`&String`). + // So it is not surprising that matching the reference implies that the lock needs to be held + // until the end of the block. match s.lock().deref().deref() { - //~^ ERROR: temporary with significant `Drop` in `match` scrutinee will live until the - //~| NOTE: this might lead to deadlocks or other unexpected behavior matcher => println!("Value is {}", s.lock().deref()), _ => println!("Value was not a match"), }; @@ -639,13 +645,12 @@ fn should_trigger_lint_for_non_ref_move_and_clone_suggestion() { }; } -fn should_trigger_lint_for_read_write_lock_for_loop() { - // For-in loops desugar to match expressions and are prone to the type of deadlock this lint is - // designed to look for. +fn should_not_trigger_lint_for_read_write_lock_for_loop() { let rwlock = RwLock::>::new(vec!["1".to_string()]); + // Should not trigger lint. Since we're iterating over the data, it's obvious that the lock + // has to be held until the iteration finishes. + // https://github.com/rust-lang/rust-clippy/issues/8987 for s in rwlock.read().unwrap().iter() { - //~^ ERROR: temporary with significant `Drop` in `for` loop condition will live until - //~| NOTE: this might lead to deadlocks or other unexpected behavior println!("{}", s); } } @@ -731,4 +736,69 @@ fn should_not_trigger_for_significant_drop_ref() { }; } +struct Foo<'a>(&'a Vec); + +impl<'a> Foo<'a> { + fn copy_old_lifetime(&self) -> &'a Vec { + self.0 + } + + fn reborrow_new_lifetime(&self) -> &Vec { + self.0 + } +} + +fn should_trigger_lint_if_and_only_if_lifetime_is_irrelevant() { + let vec = Vec::new(); + let mutex = Mutex::new(Foo(&vec)); + + // Should trigger lint even if `copy_old_lifetime()` has a lifetime, as the lifetime of + // `&vec` is unrelated to the temporary with significant drop (i.e., the `MutexGuard`). + for val in mutex.lock().unwrap().copy_old_lifetime() { + //~^ ERROR: temporary with significant `Drop` in `for` loop condition will live until the + //~| NOTE: this might lead to deadlocks or other unexpected behavior + println!("{}", val); + } + + // Should not trigger lint because `reborrow_new_lifetime()` has a lifetime and the + // lifetime is related to the temporary with significant drop (i.e., the `MutexGuard`). + for val in mutex.lock().unwrap().reborrow_new_lifetime() { + println!("{}", val); + } +} + +fn should_not_trigger_lint_for_complex_lifetime() { + let mutex = Mutex::new(vec!["hello".to_owned()]); + let string = "world".to_owned(); + + // Should not trigger lint due to the relevant lifetime. + for c in mutex.lock().unwrap().first().unwrap().chars() { + println!("{}", c); + } + + // Should trigger lint due to the irrelevant lifetime. + // + // FIXME: The lifetime is too complex to analyze. In order to avoid false positives, we do not + // trigger lint. + for c in mutex.lock().unwrap().first().map(|_| &string).unwrap().chars() { + println!("{}", c); + } +} + +fn should_not_trigger_lint_with_explicit_drop() { + let mutex = Mutex::new(vec![1]); + + // Should not trigger lint since the drop explicitly happens. + for val in [drop(mutex.lock().unwrap()), ()] { + println!("{:?}", val); + } + + // Should trigger lint if there is no explicit drop. + for val in [mutex.lock().unwrap()[0], 2] { + //~^ ERROR: temporary with significant `Drop` in `for` loop condition will live until the + //~| NOTE: this might lead to deadlocks or other unexpected behavior + println!("{:?}", val); + } +} + fn main() {} diff --git a/tests/ui/significant_drop_in_scrutinee.stderr b/tests/ui/significant_drop_in_scrutinee.stderr index 811bb065527..4a483e79d8a 100644 --- a/tests/ui/significant_drop_in_scrutinee.stderr +++ b/tests/ui/significant_drop_in_scrutinee.stderr @@ -160,42 +160,10 @@ LL ~ match (mutex1.lock().unwrap().s.len(), true, value) { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:279:15 - | -LL | match mutex3.lock().unwrap().s.as_str() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -... -LL | mutex1.lock().unwrap().s.len(); - | ---------------------- another value with significant `Drop` created here -LL | mutex2.lock().unwrap().s.len(); - | ---------------------- another value with significant `Drop` created here -... -LL | }; - | - temporary lives until here - | - = note: this might lead to deadlocks or other unexpected behavior - -error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:291:22 - | -LL | match (true, mutex3.lock().unwrap().s.as_str()) { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -... -LL | mutex1.lock().unwrap().s.len(); - | ---------------------- another value with significant `Drop` created here -LL | mutex2.lock().unwrap().s.len(); - | ---------------------- another value with significant `Drop` created here -... -LL | }; - | - temporary lives until here - | - = note: this might lead to deadlocks or other unexpected behavior - -error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:312:11 + --> tests/ui/significant_drop_in_scrutinee.rs:319:11 | LL | match mutex.lock().unwrap().s.len() > 1 { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | mutex.lock().unwrap().s.len(); | --------------------- another value with significant `Drop` created here @@ -206,15 +174,15 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ let value = mutex.lock().unwrap().s.len() > 1; -LL ~ match value { +LL ~ let value = mutex.lock().unwrap().s.len(); +LL ~ match value > 1 { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:321:11 + --> tests/ui/significant_drop_in_scrutinee.rs:328:15 | LL | match 1 < mutex.lock().unwrap().s.len() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | mutex.lock().unwrap().s.len(); | --------------------- another value with significant `Drop` created here @@ -225,15 +193,15 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ let value = 1 < mutex.lock().unwrap().s.len(); -LL ~ match value { +LL ~ let value = mutex.lock().unwrap().s.len(); +LL ~ match 1 < value { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:341:11 + --> tests/ui/significant_drop_in_scrutinee.rs:348:11 | LL | match mutex1.lock().unwrap().s.len() < mutex2.lock().unwrap().s.len() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | mutex1.lock().unwrap().s.len(), | ---------------------- another value with significant `Drop` created here @@ -246,15 +214,36 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ let value = mutex1.lock().unwrap().s.len() < mutex2.lock().unwrap().s.len(); -LL ~ match value { +LL ~ let value = mutex1.lock().unwrap().s.len(); +LL ~ match value < mutex2.lock().unwrap().s.len() { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:354:11 + --> tests/ui/significant_drop_in_scrutinee.rs:348:44 + | +LL | match mutex1.lock().unwrap().s.len() < mutex2.lock().unwrap().s.len() { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +... +LL | mutex1.lock().unwrap().s.len(), + | ---------------------- another value with significant `Drop` created here +LL | mutex2.lock().unwrap().s.len() + | ---------------------- another value with significant `Drop` created here +... +LL | }; + | - temporary lives until here + | + = note: this might lead to deadlocks or other unexpected behavior +help: try moving the temporary above the match + | +LL ~ let value = mutex2.lock().unwrap().s.len(); +LL ~ match mutex1.lock().unwrap().s.len() < value { + | + +error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression + --> tests/ui/significant_drop_in_scrutinee.rs:361:11 | LL | match mutex1.lock().unwrap().s.len() >= mutex2.lock().unwrap().s.len() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | mutex1.lock().unwrap().s.len(), | ---------------------- another value with significant `Drop` created here @@ -267,15 +256,36 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ let value = mutex1.lock().unwrap().s.len() >= mutex2.lock().unwrap().s.len(); -LL ~ match value { +LL ~ let value = mutex1.lock().unwrap().s.len(); +LL ~ match value >= mutex2.lock().unwrap().s.len() { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:391:11 + --> tests/ui/significant_drop_in_scrutinee.rs:361:45 + | +LL | match mutex1.lock().unwrap().s.len() >= mutex2.lock().unwrap().s.len() { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +... +LL | mutex1.lock().unwrap().s.len(), + | ---------------------- another value with significant `Drop` created here +LL | mutex2.lock().unwrap().s.len() + | ---------------------- another value with significant `Drop` created here +... +LL | }; + | - temporary lives until here + | + = note: this might lead to deadlocks or other unexpected behavior +help: try moving the temporary above the match + | +LL ~ let value = mutex2.lock().unwrap().s.len(); +LL ~ match mutex1.lock().unwrap().s.len() >= value { + | + +error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression + --> tests/ui/significant_drop_in_scrutinee.rs:398:11 | LL | match get_mutex_guard().s.len() > 1 { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^^^ ... LL | mutex1.lock().unwrap().s.len(); | ---------------------- another value with significant `Drop` created here @@ -286,12 +296,12 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ let value = get_mutex_guard().s.len() > 1; -LL ~ match value { +LL ~ let value = get_mutex_guard().s.len(); +LL ~ match value > 1 { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:410:11 + --> tests/ui/significant_drop_in_scrutinee.rs:417:11 | LL | match match i { | ___________^ @@ -299,9 +309,9 @@ LL | | LL | | LL | | 100 => mutex1.lock().unwrap(), ... | +LL | | .s LL | | .len() -LL | | > 1 - | |___________^ + | |__________^ ... LL | mutex1.lock().unwrap().s.len(); | ---------------------- another value with significant `Drop` created here @@ -319,13 +329,12 @@ LL + 100 => mutex1.lock().unwrap(), LL + _ => mutex2.lock().unwrap(), LL + } LL + .s -LL + .len() -LL + > 1; +LL + .len(); LL ~ match value | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:438:11 + --> tests/ui/significant_drop_in_scrutinee.rs:445:11 | LL | match if i > 1 { | ___________^ @@ -333,9 +342,9 @@ LL | | LL | | LL | | mutex1.lock().unwrap() ... | +LL | | .s LL | | .len() -LL | | > 1 - | |___________^ + | |__________^ ... LL | mutex1.lock().unwrap().s.len(); | ---------------------- another value with significant `Drop` created here @@ -354,13 +363,12 @@ LL + } else { LL + mutex2.lock().unwrap() LL + } LL + .s -LL + .len() -LL + > 1; +LL + .len(); LL ~ match value | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:494:11 + --> tests/ui/significant_drop_in_scrutinee.rs:501:11 | LL | match s.lock().deref().deref() { | ^^^^^^^^^^^^^^^^^^^^^^^^ @@ -374,25 +382,11 @@ LL | }; help: try moving the temporary above the match and create a copy | LL ~ let value = *s.lock().deref().deref(); -LL ~ match value { +LL ~ match (&value) { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:524:11 - | -LL | match s.lock().deref().deref() { - | ^^^^^^^^^^^^^^^^^^^^^^^^ -... -LL | matcher => println!("Value is {}", s.lock().deref()), - | -------- another value with significant `Drop` created here -LL | _ => println!("Value was not a match"), -LL | }; - | - temporary lives until here - | - = note: this might lead to deadlocks or other unexpected behavior - -error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:545:11 + --> tests/ui/significant_drop_in_scrutinee.rs:551:11 | LL | match mutex.lock().unwrap().i = i { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -411,10 +405,10 @@ LL ~ match () { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:553:11 + --> tests/ui/significant_drop_in_scrutinee.rs:559:15 | LL | match i = mutex.lock().unwrap().i { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^ ... LL | println!("{}", mutex.lock().unwrap().i); | --------------------- another value with significant `Drop` created here @@ -425,12 +419,12 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ i = mutex.lock().unwrap().i; -LL ~ match () { +LL ~ let value = mutex.lock().unwrap().i; +LL ~ match i = value { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:561:11 + --> tests/ui/significant_drop_in_scrutinee.rs:567:11 | LL | match mutex.lock().unwrap().i += 1 { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -449,10 +443,10 @@ LL ~ match () { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:569:11 + --> tests/ui/significant_drop_in_scrutinee.rs:575:16 | LL | match i += mutex.lock().unwrap().i { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + | ^^^^^^^^^^^^^^^^^^^^^^^ ... LL | println!("{}", mutex.lock().unwrap().i); | --------------------- another value with significant `Drop` created here @@ -463,12 +457,12 @@ LL | }; = note: this might lead to deadlocks or other unexpected behavior help: try moving the temporary above the match | -LL ~ i += mutex.lock().unwrap().i; -LL ~ match () { +LL ~ let value = mutex.lock().unwrap().i; +LL ~ match i += value { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:634:11 + --> tests/ui/significant_drop_in_scrutinee.rs:640:11 | LL | match rwlock.read().unwrap().to_number() { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -477,20 +471,14 @@ LL | }; | - temporary lives until here | = note: this might lead to deadlocks or other unexpected behavior - -error: temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression - --> tests/ui/significant_drop_in_scrutinee.rs:646:14 +help: try moving the temporary above the match | -LL | for s in rwlock.read().unwrap().iter() { - | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -... -LL | } - | - temporary lives until here +LL ~ let value = rwlock.read().unwrap().to_number(); +LL ~ match value { | - = note: this might lead to deadlocks or other unexpected behavior error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:663:11 + --> tests/ui/significant_drop_in_scrutinee.rs:668:11 | LL | match mutex.lock().unwrap().foo() { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ @@ -506,7 +494,7 @@ LL ~ match value { | error: temporary with significant `Drop` in `match` scrutinee will live until the end of the `match` expression - --> tests/ui/significant_drop_in_scrutinee.rs:726:11 + --> tests/ui/significant_drop_in_scrutinee.rs:731:11 | LL | match guard.take().len() { | ^^^^^^^^^^^^^^^^^^ @@ -521,5 +509,37 @@ LL ~ let value = guard.take().len(); LL ~ match value { | +error: temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression + --> tests/ui/significant_drop_in_scrutinee.rs:757:16 + | +LL | for val in mutex.lock().unwrap().copy_old_lifetime() { + | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ +... +LL | } + | - temporary lives until here + | + = note: this might lead to deadlocks or other unexpected behavior +help: try moving the temporary above the match + | +LL ~ let value = mutex.lock().unwrap().copy_old_lifetime(); +LL ~ for val in value { + | + +error: temporary with significant `Drop` in `for` loop condition will live until the end of the `for` expression + --> tests/ui/significant_drop_in_scrutinee.rs:797:17 + | +LL | for val in [mutex.lock().unwrap()[0], 2] { + | ^^^^^^^^^^^^^^^^^^^^^^^^ +... +LL | } + | - temporary lives until here + | + = note: this might lead to deadlocks or other unexpected behavior +help: try moving the temporary above the match + | +LL ~ let value = mutex.lock().unwrap()[0]; +LL ~ for val in [value, 2] { + | + error: aborting due to 27 previous errors