1 use crate::utils::sugg::Sugg;
3 differing_macro_contexts, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty, SpanlessEq,
5 use if_chain::if_chain;
8 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
10 use rustc::{declare_tool_lint, lint_array};
11 use rustc_errors::Applicability;
13 declare_clippy_lint! {
14 /// **What it does:** Checks for manual swapping.
16 /// **Why is this bad?** The `std::mem::swap` function exposes the intent better
17 /// without deinitializing or copying either variable.
19 /// **Known problems:** None.
27 /// Use std::mem::swap():
29 /// std::mem::swap(&mut a, &mut b);
33 "manual swap of two variables"
36 declare_clippy_lint! {
37 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
39 /// **Why is this bad?** This looks like a failed attempt to swap.
41 /// **Known problems:** None.
50 "`foo = bar; bar = foo` sequence"
53 #[derive(Copy, Clone)]
56 impl LintPass for Swap {
57 fn get_lints(&self) -> LintArray {
58 lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
61 fn name(&self) -> &'static str {
66 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
67 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
68 check_manual_swap(cx, block);
69 check_suspicious_swap(cx, block);
73 /// Implementation of the `MANUAL_SWAP` lint.
74 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
75 for w in block.stmts.windows(3) {
78 if let StmtKind::Local(ref tmp) = w[0].node;
79 if let Some(ref tmp_init) = tmp.init;
80 if let PatKind::Binding(.., ident, None) = tmp.pat.node;
83 if let StmtKind::Semi(ref first) = w[1].node;
84 if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
87 if let StmtKind::Semi(ref second) = w[2].node;
88 if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
89 if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
90 if rhs2.segments.len() == 1;
92 if ident.as_str() == rhs2.segments[0].ident.as_str();
93 if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
94 if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
96 fn check_for_slice<'a>(
97 cx: &LateContext<'_, '_>,
100 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
101 if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
102 if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
103 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
104 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
106 if matches!(ty.sty, ty::Slice(_)) ||
107 matches!(ty.sty, ty::Array(_, _)) ||
108 match_type(cx, ty, &paths::VEC) ||
109 match_type(cx, ty, &paths::VEC_DEQUE) {
110 return Some((lhs1, idx1, idx2));
119 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
120 if let Some(slice) = Sugg::hir_opt(cx, slice) {
122 format!(" elements of `{}`", slice),
123 format!("{}.swap({}, {})",
125 snippet(cx, idx1.span, ".."),
126 snippet(cx, idx2.span, "..")))
128 (false, String::new(), String::new())
130 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
131 (true, format!(" `{}` and `{}`", first, second),
132 format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
134 (true, String::new(), String::new())
137 let span = w[0].span.to(second.span);
139 span_lint_and_then(cx,
142 &format!("this looks like you are swapping{} manually", what),
144 if !sugg.is_empty() {
149 Applicability::Unspecified,
153 db.note("or maybe you should use `std::mem::replace`?");
162 /// Implementation of the `ALMOST_SWAPPED` lint.
163 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
164 for w in block.stmts.windows(2) {
166 if let StmtKind::Semi(ref first) = w[0].node;
167 if let StmtKind::Semi(ref second) = w[1].node;
168 if !differing_macro_contexts(first.span, second.span);
169 if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
170 if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
171 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
172 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
174 let lhs0 = Sugg::hir_opt(cx, lhs0);
175 let rhs0 = Sugg::hir_opt(cx, rhs0);
176 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
178 format!(" `{}` and `{}`", first, second),
179 first.mut_addr().to_string(),
180 second.mut_addr().to_string(),
183 (String::new(), String::new(), String::new())
186 let span = first.span.to(second.span);
188 span_lint_and_then(cx,
191 &format!("this looks like you are trying to swap{}", what),
193 if !what.is_empty() {
198 "std::mem::swap({}, {})",
202 Applicability::MaybeIncorrect,
204 db.note("or maybe you should use `std::mem::replace`?");