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_lint_pass, declare_tool_lint};
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.
30 /// Use std::mem::swap():
34 /// std::mem::swap(&mut a, &mut b);
38 "manual swap of two variables"
41 declare_clippy_lint! {
42 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
44 /// **Why is this bad?** This looks like a failed attempt to swap.
46 /// **Known problems:** None.
55 /// Could be written as:
59 /// std::mem::swap(&mut a, &mut b);
63 "`foo = bar; bar = foo` sequence"
66 declare_lint_pass!(Swap => [MANUAL_SWAP, ALMOST_SWAPPED]);
68 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
69 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
70 check_manual_swap(cx, block);
71 check_suspicious_swap(cx, block);
75 /// Implementation of the `MANUAL_SWAP` lint.
76 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
77 for w in block.stmts.windows(3) {
80 if let StmtKind::Local(ref tmp) = w[0].node;
81 if let Some(ref tmp_init) = tmp.init;
82 if let PatKind::Binding(.., ident, None) = tmp.pat.node;
85 if let StmtKind::Semi(ref first) = w[1].node;
86 if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
89 if let StmtKind::Semi(ref second) = w[2].node;
90 if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
91 if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
92 if rhs2.segments.len() == 1;
94 if ident.as_str() == rhs2.segments[0].ident.as_str();
95 if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
96 if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
98 fn check_for_slice<'a>(
99 cx: &LateContext<'_, '_>,
102 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
103 if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
104 if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
105 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
106 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
108 if matches!(ty.sty, ty::Slice(_)) ||
109 matches!(ty.sty, ty::Array(_, _)) ||
110 match_type(cx, ty, &paths::VEC) ||
111 match_type(cx, ty, &paths::VEC_DEQUE) {
112 return Some((lhs1, idx1, idx2));
121 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
122 if let Some(slice) = Sugg::hir_opt(cx, slice) {
124 format!(" elements of `{}`", slice),
125 format!("{}.swap({}, {})",
127 snippet(cx, idx1.span, ".."),
128 snippet(cx, idx2.span, "..")))
130 (false, String::new(), String::new())
132 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
133 (true, format!(" `{}` and `{}`", first, second),
134 format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
136 (true, String::new(), String::new())
139 let span = w[0].span.to(second.span);
141 span_lint_and_then(cx,
144 &format!("this looks like you are swapping{} manually", what),
146 if !sugg.is_empty() {
151 Applicability::Unspecified,
155 db.note("or maybe you should use `std::mem::replace`?");
164 /// Implementation of the `ALMOST_SWAPPED` lint.
165 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
166 for w in block.stmts.windows(2) {
168 if let StmtKind::Semi(ref first) = w[0].node;
169 if let StmtKind::Semi(ref second) = w[1].node;
170 if !differing_macro_contexts(first.span, second.span);
171 if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
172 if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
173 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
174 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
176 let lhs0 = Sugg::hir_opt(cx, lhs0);
177 let rhs0 = Sugg::hir_opt(cx, rhs0);
178 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
180 format!(" `{}` and `{}`", first, second),
181 first.mut_addr().to_string(),
182 second.mut_addr().to_string(),
185 (String::new(), String::new(), String::new())
188 let span = first.span.to(second.span);
190 span_lint_and_then(cx,
193 &format!("this looks like you are trying to swap{}", what),
195 if !what.is_empty() {
200 "std::mem::swap({}, {})",
204 Applicability::MaybeIncorrect,
206 db.note("or maybe you should use `std::mem::replace`?");