1 use crate::utils::sugg::Sugg;
3 differing_macro_contexts, is_type_diagnostic_item, snippet_with_applicability, span_lint_and_then, walk_ptrs_ty,
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, StmtKind};
9 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
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 /// If swapping is intended, use `swap()` instead:
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<'tcx> LateLintPass<'tcx> for Swap {
69 fn check_block(&mut self, cx: &LateContext<'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].kind;
81 if let Some(ref tmp_init) = tmp.init;
82 if let PatKind::Binding(.., ident, None) = tmp.pat.kind;
85 if let StmtKind::Semi(ref first) = w[1].kind;
86 if let ExprKind::Assign(ref lhs1, ref rhs1, _) = first.kind;
89 if let StmtKind::Semi(ref second) = w[2].kind;
90 if let ExprKind::Assign(ref lhs2, ref rhs2, _) = second.kind;
91 if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.kind;
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 if let ExprKind::Field(ref lhs1, _) = lhs1.kind {
99 if let ExprKind::Field(ref lhs2, _) = lhs2.kind {
100 if lhs1.hir_id.owner == lhs2.hir_id.owner {
106 let mut applicability = Applicability::MachineApplicable;
108 let slice = check_for_slice(cx, lhs1, lhs2);
109 let (replace, what, sugg) = if let Slice::NotSwappable = slice {
111 } else if let Slice::Swappable(slice, idx1, idx2) = slice {
112 if let Some(slice) = Sugg::hir_opt(cx, slice) {
115 format!(" elements of `{}`", slice),
119 snippet_with_applicability(cx, idx1.span, "..", &mut applicability),
120 snippet_with_applicability(cx, idx2.span, "..", &mut applicability),
124 (false, String::new(), String::new())
126 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
129 format!(" `{}` and `{}`", first, second),
130 format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()),
133 (true, String::new(), String::new())
136 let span = w[0].span.to(second.span);
142 &format!("this looks like you are swapping{} manually", what),
144 if !sugg.is_empty() {
145 diag.span_suggestion(
153 diag.note("or maybe you should use `std::mem::replace`?");
164 /// `slice.swap(idx1, idx2)` can be used
169 /// # let mut a = vec![0, 1];
173 /// // can be written as
176 Swappable(&'a Expr<'a>, &'a Expr<'a>, &'a Expr<'a>),
177 /// The `swap` function cannot be used.
182 /// # let mut a = [vec![1, 2], vec![3, 4]];
184 /// a[0][1] = a[1][0];
192 /// Checks if both expressions are index operations into "slice-like" types.
193 fn check_for_slice<'a>(cx: &LateContext<'_>, lhs1: &'a Expr<'_>, lhs2: &'a Expr<'_>) -> Slice<'a> {
194 if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.kind {
195 if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.kind {
196 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
197 let ty = walk_ptrs_ty(cx.typeck_results().expr_ty(lhs1));
199 if matches!(ty.kind, ty::Slice(_))
200 || matches!(ty.kind, ty::Array(_, _))
201 || is_type_diagnostic_item(cx, ty, sym!(vec_type))
202 || is_type_diagnostic_item(cx, ty, sym!(vecdeque_type))
204 return Slice::Swappable(lhs1, idx1, idx2);
207 return Slice::NotSwappable;
215 /// Implementation of the `ALMOST_SWAPPED` lint.
216 fn check_suspicious_swap(cx: &LateContext<'_>, block: &Block<'_>) {
217 for w in block.stmts.windows(2) {
219 if let StmtKind::Semi(ref first) = w[0].kind;
220 if let StmtKind::Semi(ref second) = w[1].kind;
221 if !differing_macro_contexts(first.span, second.span);
222 if let ExprKind::Assign(ref lhs0, ref rhs0, _) = first.kind;
223 if let ExprKind::Assign(ref lhs1, ref rhs1, _) = second.kind;
224 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
225 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
227 let lhs0 = Sugg::hir_opt(cx, lhs0);
228 let rhs0 = Sugg::hir_opt(cx, rhs0);
229 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
231 format!(" `{}` and `{}`", first, second),
232 first.mut_addr().to_string(),
233 second.mut_addr().to_string(),
236 (String::new(), String::new(), String::new())
239 let span = first.span.to(second.span);
241 span_lint_and_then(cx,
244 &format!("this looks like you are trying to swap{}", what),
246 if !what.is_empty() {
247 diag.span_suggestion(
251 "std::mem::swap({}, {})",
255 Applicability::MaybeIncorrect,
257 diag.note("or maybe you should use `std::mem::replace`?");