|
| 1 | +use std::mem::swap; |
| 2 | + |
| 3 | +use clippy_utils::diagnostics::span_lint_and_then; |
| 4 | +use rustc_ast::UnOp; |
| 5 | +use rustc_hir::def::Res; |
| 6 | +use rustc_hir::intravisit::{self, Visitor}; |
| 7 | +use rustc_hir::{Block, Expr, ExprKind, LetStmt, Pat, PatKind, QPath, StmtKind}; |
| 8 | +use rustc_lint::{LateContext, LateLintPass}; |
| 9 | +use rustc_session::declare_lint_pass; |
| 10 | +use rustc_span::Span; |
| 11 | + |
| 12 | +declare_clippy_lint! { |
| 13 | + /// ### What it does |
| 14 | + /// Edition 2024 introduces a new rule with drop orders for values generated in tail expressions |
| 15 | + /// of blocks. |
| 16 | + /// Now the values will be dropped first, before the local variable bindings were dropped. |
| 17 | + /// |
| 18 | + /// This lint looks for those values generated at the tail expression location, that of type |
| 19 | + /// with a significant `Drop` implementation, such as locks. |
| 20 | + /// In case there are also local variables of type with significant `Drop` implementation as well, |
| 21 | + /// this lint warns you of a potential transposition in the drop order. |
| 22 | + /// Your discretion on the new drop order introduced by Edition 2024 is required. |
| 23 | + /// |
| 24 | + /// ### Why is this bad? |
| 25 | + /// Values of type with significant `Drop` implementation has an ill-specified drop order that |
| 26 | + /// come after those of local variables. |
| 27 | + /// Edition 2024 moves them, so that they are dropped first before dropping local variables. |
| 28 | + /// |
| 29 | + /// ### Example |
| 30 | + /// ```ignore |
| 31 | + /// fn edition_2024() -> i32 { |
| 32 | + /// let mutex = std::sync::Mutex::new(vec![0]); |
| 33 | + /// mutex.lock().unwrap()[0] |
| 34 | + /// } |
| 35 | + /// ``` |
| 36 | + /// This lint only points out the issue with `mutex.lock()`, which will be dropped before `mutex` does. |
| 37 | + /// No fix will be proposed. |
| 38 | + /// However, the most probable fix is to hoist `mutex.lock()` into its own local variable binding. |
| 39 | + /// ```no_run |
| 40 | + /// fn edition_2024() -> i32 { |
| 41 | + /// let mutex = std::sync::Mutex::new(vec![0]); |
| 42 | + /// let guard = mutex.lock().unwrap(); |
| 43 | + /// guard[0] |
| 44 | + /// } |
| 45 | + /// ``` |
| 46 | + #[clippy::version = "1.82.0"] |
| 47 | + pub TAIL_EXPR_DROP_ORDER, |
| 48 | + nursery, |
| 49 | + "Detect and warn on significant change in drop order in tail expression location" |
| 50 | +} |
| 51 | + |
| 52 | +declare_lint_pass!(TailExprDropOrder => [TAIL_EXPR_DROP_ORDER]); |
| 53 | + |
| 54 | +impl<'tcx> LateLintPass<'tcx> for TailExprDropOrder { |
| 55 | + fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) { |
| 56 | + LintVisitor { |
| 57 | + cx, |
| 58 | + locals: <_>::default(), |
| 59 | + } |
| 60 | + .check_block_inner(block); |
| 61 | + } |
| 62 | +} |
| 63 | + |
| 64 | +struct LintVisitor<'tcx, 'a> { |
| 65 | + cx: &'a LateContext<'tcx>, |
| 66 | + locals: Vec<Span>, |
| 67 | +} |
| 68 | + |
| 69 | +struct LocalCollector<'tcx, 'a> { |
| 70 | + cx: &'a LateContext<'tcx>, |
| 71 | + locals: &'a mut Vec<Span>, |
| 72 | +} |
| 73 | + |
| 74 | +impl<'tcx, 'a> Visitor<'tcx> for LocalCollector<'tcx, 'a> { |
| 75 | + type Result = (); |
| 76 | + fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) { |
| 77 | + if let PatKind::Binding(_binding_mode, id, ident, pat) = pat.kind { |
| 78 | + let ty = self.cx.typeck_results().node_type(id); |
| 79 | + if ty.has_significant_drop(self.cx.tcx, self.cx.param_env) { |
| 80 | + self.locals.push(ident.span); |
| 81 | + } |
| 82 | + if let Some(pat) = pat { |
| 83 | + self.visit_pat(pat); |
| 84 | + } |
| 85 | + } else { |
| 86 | + intravisit::walk_pat(self, pat); |
| 87 | + } |
| 88 | + } |
| 89 | +} |
| 90 | + |
| 91 | +impl<'tcx, 'a> Visitor<'tcx> for LintVisitor<'tcx, 'a> { |
| 92 | + fn visit_block(&mut self, block: &'tcx Block<'tcx>) { |
| 93 | + let mut locals = <_>::default(); |
| 94 | + swap(&mut locals, &mut self.locals); |
| 95 | + self.check_block_inner(block); |
| 96 | + swap(&mut locals, &mut self.locals); |
| 97 | + } |
| 98 | + fn visit_local(&mut self, local: &'tcx LetStmt<'tcx>) { |
| 99 | + LocalCollector { |
| 100 | + cx: self.cx, |
| 101 | + locals: &mut self.locals, |
| 102 | + } |
| 103 | + .visit_local(local); |
| 104 | + } |
| 105 | +} |
| 106 | + |
| 107 | +impl<'tcx, 'a> LintVisitor<'tcx, 'a> { |
| 108 | + fn check_block_inner(&mut self, block: &Block<'tcx>) { |
| 109 | + if !block.span.at_least_rust_2024() { |
| 110 | + // We only lint for Edition 2024 onwards |
| 111 | + return; |
| 112 | + } |
| 113 | + let Some(tail_expr) = block.expr else { return }; |
| 114 | + for stmt in block.stmts { |
| 115 | + match stmt.kind { |
| 116 | + StmtKind::Let(let_stmt) => self.visit_local(let_stmt), |
| 117 | + StmtKind::Item(_) => {}, |
| 118 | + StmtKind::Expr(e) | StmtKind::Semi(e) => self.visit_expr(e), |
| 119 | + } |
| 120 | + } |
| 121 | + if self.locals.is_empty() { |
| 122 | + return; |
| 123 | + } |
| 124 | + LintTailExpr { |
| 125 | + cx: self.cx, |
| 126 | + locals: &self.locals, |
| 127 | + } |
| 128 | + .visit_expr(tail_expr); |
| 129 | + } |
| 130 | +} |
| 131 | + |
| 132 | +struct LintTailExpr<'tcx, 'a> { |
| 133 | + cx: &'a LateContext<'tcx>, |
| 134 | + locals: &'a [Span], |
| 135 | +} |
| 136 | + |
| 137 | +impl<'tcx, 'a> LintTailExpr<'tcx, 'a> { |
| 138 | + fn expr_eventually_point_into_local(mut expr: &Expr<'tcx>) -> bool { |
| 139 | + loop { |
| 140 | + match expr.kind { |
| 141 | + ExprKind::Index(access, _, _) | ExprKind::Field(access, _) => expr = access, |
| 142 | + ExprKind::AddrOf(_, _, referee) | ExprKind::Unary(UnOp::Deref, referee) => expr = referee, |
| 143 | + ExprKind::Path(_) |
| 144 | + if let ExprKind::Path(QPath::Resolved(_, path)) = expr.kind |
| 145 | + && let [local, ..] = path.segments |
| 146 | + && let Res::Local(_) = local.res => |
| 147 | + { |
| 148 | + return true; |
| 149 | + }, |
| 150 | + _ => return false, |
| 151 | + } |
| 152 | + } |
| 153 | + } |
| 154 | + |
| 155 | + fn expr_generates_nonlocal_droppy_value(&self, expr: &Expr<'tcx>) -> bool { |
| 156 | + if Self::expr_eventually_point_into_local(expr) { |
| 157 | + return false; |
| 158 | + } |
| 159 | + self.cx |
| 160 | + .typeck_results() |
| 161 | + .expr_ty(expr) |
| 162 | + .has_significant_drop(self.cx.tcx, self.cx.param_env) |
| 163 | + } |
| 164 | +} |
| 165 | + |
| 166 | +impl<'tcx, 'a> Visitor<'tcx> for LintTailExpr<'tcx, 'a> { |
| 167 | + fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) { |
| 168 | + if self.expr_generates_nonlocal_droppy_value(expr) { |
| 169 | + span_lint_and_then( |
| 170 | + self.cx, |
| 171 | + TAIL_EXPR_DROP_ORDER, |
| 172 | + expr.span, |
| 173 | + "discretion required on this expression which generates a value with a significant drop implementation", |
| 174 | + |diag| { |
| 175 | + diag.span_help(self.locals.to_vec(), "one or more locals with a significant drop implementation will observe a visible change in drop order"); |
| 176 | + }, |
| 177 | + ); |
| 178 | + return; |
| 179 | + } |
| 180 | + match expr.kind { |
| 181 | + ExprKind::ConstBlock(_) |
| 182 | + | ExprKind::Array(_) |
| 183 | + | ExprKind::Break(_, _) |
| 184 | + | ExprKind::Continue(_) |
| 185 | + | ExprKind::Ret(_) |
| 186 | + | ExprKind::Become(_) |
| 187 | + | ExprKind::Yield(_, _) |
| 188 | + | ExprKind::InlineAsm(_) |
| 189 | + | ExprKind::If(_, _, _) |
| 190 | + | ExprKind::Loop(_, _, _, _) |
| 191 | + | ExprKind::Match(_, _, _) |
| 192 | + | ExprKind::Closure(_) |
| 193 | + | ExprKind::DropTemps(_) |
| 194 | + | ExprKind::OffsetOf(_, _) |
| 195 | + | ExprKind::Assign(_, _, _) |
| 196 | + | ExprKind::AssignOp(_, _, _) |
| 197 | + | ExprKind::Lit(_) |
| 198 | + | ExprKind::Err(_) => {}, |
| 199 | + |
| 200 | + ExprKind::MethodCall(_, _, _, _) |
| 201 | + | ExprKind::Call(_, _) |
| 202 | + | ExprKind::Type(_, _) |
| 203 | + | ExprKind::Tup(_) |
| 204 | + | ExprKind::Binary(_, _, _) |
| 205 | + | ExprKind::Unary(_, _) |
| 206 | + | ExprKind::Path(_) |
| 207 | + | ExprKind::Let(_) |
| 208 | + | ExprKind::Cast(_, _) |
| 209 | + | ExprKind::Field(_, _) |
| 210 | + | ExprKind::Index(_, _, _) |
| 211 | + | ExprKind::AddrOf(_, _, _) |
| 212 | + | ExprKind::Struct(_, _, _) |
| 213 | + | ExprKind::Repeat(_, _) => intravisit::walk_expr(self, expr), |
| 214 | + |
| 215 | + ExprKind::Block(block, _) => LintVisitor { |
| 216 | + cx: self.cx, |
| 217 | + locals: <_>::default(), |
| 218 | + } |
| 219 | + .check_block_inner(block), |
| 220 | + } |
| 221 | + } |
| 222 | + fn visit_block(&mut self, block: &'tcx Block<'tcx>) { |
| 223 | + LintVisitor { |
| 224 | + cx: self.cx, |
| 225 | + locals: <_>::default(), |
| 226 | + } |
| 227 | + .check_block_inner(block); |
| 228 | + } |
| 229 | +} |
0 commit comments