1 use clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
2 use clippy_utils::source::snippet_with_applicability;
3 use clippy_utils::sugg::Sugg;
4 use clippy_utils::ty::is_type_diagnostic_item;
5 use clippy_utils::{can_mut_borrow_both, differing_macro_contexts, eq_expr_value, std_or_core};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{BinOpKind, Block, Expr, ExprKind, PatKind, QPath, Stmt, StmtKind};
9 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
12 use rustc_span::source_map::Spanned;
13 use rustc_span::{sym, Span};
15 declare_clippy_lint! {
17 /// Checks for manual swapping.
19 /// ### Why is this bad?
20 /// The `std::mem::swap` function exposes the intent better
21 /// without deinitializing or copying either variable.
32 /// Use std::mem::swap():
36 /// std::mem::swap(&mut a, &mut b);
38 #[clippy::version = "pre 1.29.0"]
41 "manual swap of two variables"
44 declare_clippy_lint! {
46 /// Checks for `foo = bar; bar = foo` sequences.
48 /// ### Why is this bad?
49 /// This looks like a failed attempt to swap.
58 /// If swapping is intended, use `swap()` instead:
62 /// std::mem::swap(&mut a, &mut b);
64 #[clippy::version = "pre 1.29.0"]
67 "`foo = bar; bar = foo` sequence"
70 declare_lint_pass!(Swap => [MANUAL_SWAP, ALMOST_SWAPPED]);
72 impl<'tcx> LateLintPass<'tcx> for Swap {
73 fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'_>) {
74 check_manual_swap(cx, block);
75 check_suspicious_swap(cx, block);
76 check_xor_swap(cx, block);
80 fn generate_swap_warning(cx: &LateContext<'_>, e1: &Expr<'_>, e2: &Expr<'_>, span: Span, is_xor_based: bool) {
81 let mut applicability = Applicability::MachineApplicable;
83 if !can_mut_borrow_both(cx, e1, e2) {
84 if let ExprKind::Index(lhs1, idx1) = e1.kind {
85 if let ExprKind::Index(lhs2, idx2) = e2.kind {
86 if eq_expr_value(cx, lhs1, lhs2) {
87 let ty = cx.typeck_results().expr_ty(lhs1).peel_refs();
89 if matches!(ty.kind(), ty::Slice(_))
90 || matches!(ty.kind(), ty::Array(_, _))
91 || is_type_diagnostic_item(cx, ty, sym::Vec)
92 || is_type_diagnostic_item(cx, ty, sym::VecDeque)
94 let slice = Sugg::hir_with_applicability(cx, lhs1, "<slice>", &mut applicability);
99 &format!("this looks like you are swapping elements of `{}` manually", slice),
104 snippet_with_applicability(cx, idx1.span, "..", &mut applicability),
105 snippet_with_applicability(cx, idx2.span, "..", &mut applicability),
116 let first = Sugg::hir_with_applicability(cx, e1, "..", &mut applicability);
117 let second = Sugg::hir_with_applicability(cx, e2, "..", &mut applicability);
118 let Some(sugg) = std_or_core(cx) else { return };
124 &format!("this looks like you are swapping `{}` and `{}` manually", first, second),
126 diag.span_suggestion(
129 format!("{}::mem::swap({}, {})", sugg, first.mut_addr(), second.mut_addr()),
133 diag.note(&format!("or maybe you should use `{}::mem::replace`?", sugg));
139 /// Implementation of the `MANUAL_SWAP` lint.
140 fn check_manual_swap(cx: &LateContext<'_>, block: &Block<'_>) {
141 for w in block.stmts.windows(3) {
144 if let StmtKind::Local(tmp) = w[0].kind;
145 if let Some(tmp_init) = tmp.init;
146 if let PatKind::Binding(.., ident, None) = tmp.pat.kind;
149 if let StmtKind::Semi(first) = w[1].kind;
150 if let ExprKind::Assign(lhs1, rhs1, _) = first.kind;
153 if let StmtKind::Semi(second) = w[2].kind;
154 if let ExprKind::Assign(lhs2, rhs2, _) = second.kind;
155 if let ExprKind::Path(QPath::Resolved(None, rhs2)) = rhs2.kind;
156 if rhs2.segments.len() == 1;
158 if ident.name == rhs2.segments[0].ident.name;
159 if eq_expr_value(cx, tmp_init, lhs1);
160 if eq_expr_value(cx, rhs1, lhs2);
162 let span = w[0].span.to(second.span);
163 generate_swap_warning(cx, lhs1, lhs2, span, false);
169 /// Implementation of the `ALMOST_SWAPPED` lint.
170 fn check_suspicious_swap(cx: &LateContext<'_>, block: &Block<'_>) {
171 for w in block.stmts.windows(2) {
173 if let StmtKind::Semi(first) = w[0].kind;
174 if let StmtKind::Semi(second) = w[1].kind;
175 if !differing_macro_contexts(first.span, second.span);
176 if let ExprKind::Assign(lhs0, rhs0, _) = first.kind;
177 if let ExprKind::Assign(lhs1, rhs1, _) = second.kind;
178 if eq_expr_value(cx, lhs0, rhs1);
179 if eq_expr_value(cx, lhs1, rhs0);
181 let lhs0 = Sugg::hir_opt(cx, lhs0);
182 let rhs0 = Sugg::hir_opt(cx, rhs0);
183 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
185 format!(" `{}` and `{}`", first, second),
186 first.mut_addr().to_string(),
187 second.mut_addr().to_string(),
190 (String::new(), String::new(), String::new())
193 let span = first.span.to(second.span);
194 let Some(sugg) = std_or_core(cx) else { return };
196 span_lint_and_then(cx,
199 &format!("this looks like you are trying to swap{}", what),
201 if !what.is_empty() {
202 diag.span_suggestion(
206 "{}::mem::swap({}, {})",
211 Applicability::MaybeIncorrect,
214 &format!("or maybe you should use `{}::mem::replace`?", sugg)
223 /// Implementation of the xor case for `MANUAL_SWAP` lint.
224 fn check_xor_swap(cx: &LateContext<'_>, block: &Block<'_>) {
225 for window in block.stmts.windows(3) {
227 if let Some((lhs0, rhs0)) = extract_sides_of_xor_assign(&window[0]);
228 if let Some((lhs1, rhs1)) = extract_sides_of_xor_assign(&window[1]);
229 if let Some((lhs2, rhs2)) = extract_sides_of_xor_assign(&window[2]);
230 if eq_expr_value(cx, lhs0, rhs1);
231 if eq_expr_value(cx, lhs2, rhs1);
232 if eq_expr_value(cx, lhs1, rhs0);
233 if eq_expr_value(cx, lhs1, rhs2);
235 let span = window[0].span.to(window[2].span);
236 generate_swap_warning(cx, lhs0, rhs0, span, true);
242 /// Returns the lhs and rhs of an xor assignment statement.
243 fn extract_sides_of_xor_assign<'a, 'hir>(stmt: &'a Stmt<'hir>) -> Option<(&'a Expr<'hir>, &'a Expr<'hir>)> {
244 if let StmtKind::Semi(expr) = stmt.kind {
245 if let ExprKind::AssignOp(
247 node: BinOpKind::BitXor,
254 return Some((lhs, rhs));