1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution.
4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
7 // option. This file may not be copied, modified, or distributed
8 // except according to those terms.
10 use crate::rustc::hir::*;
11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
13 use crate::rustc::{declare_tool_lint, lint_array};
14 use crate::rustc_errors::Applicability;
15 use crate::utils::sugg::Sugg;
17 differing_macro_contexts, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty, SpanlessEq,
19 use if_chain::if_chain;
22 /// **What it does:** Checks for manual swapping.
24 /// **Why is this bad?** The `std::mem::swap` function exposes the intent better
25 /// without deinitializing or copying either variable.
27 /// **Known problems:** None.
35 /// Use std::mem::swap():
37 /// std::mem::swap(&mut a, &mut b);
39 declare_clippy_lint! {
42 "manual swap of two variables"
45 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
47 /// **Why is this bad?** This looks like a failed attempt to swap.
49 /// **Known problems:** None.
56 declare_clippy_lint! {
59 "`foo = bar; bar = foo` sequence"
62 #[derive(Copy, Clone)]
65 impl LintPass for Swap {
66 fn get_lints(&self) -> LintArray {
67 lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
71 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
72 fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
73 check_manual_swap(cx, block);
74 check_suspicious_swap(cx, block);
78 /// Implementation of the `MANUAL_SWAP` lint.
79 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
80 for w in block.stmts.windows(3) {
83 if let StmtKind::Decl(ref tmp, _) = w[0].node;
84 if let DeclKind::Local(ref tmp) = tmp.node;
85 if let Some(ref tmp_init) = tmp.init;
86 if let PatKind::Binding(_, _, ident, None) = tmp.pat.node;
89 if let StmtKind::Semi(ref first, _) = w[1].node;
90 if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
93 if let StmtKind::Semi(ref second, _) = w[2].node;
94 if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
95 if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
96 if rhs2.segments.len() == 1;
98 if ident.as_str() == rhs2.segments[0].ident.as_str();
99 if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
100 if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
102 fn check_for_slice<'a>(
103 cx: &LateContext<'_, '_>,
106 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
107 if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
108 if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
109 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
110 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
112 if matches!(ty.sty, ty::Slice(_)) ||
113 matches!(ty.sty, ty::Array(_, _)) ||
114 match_type(cx, ty, &paths::VEC) ||
115 match_type(cx, ty, &paths::VEC_DEQUE) {
116 return Some((lhs1, idx1, idx2));
125 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
126 if let Some(slice) = Sugg::hir_opt(cx, slice) {
128 format!(" elements of `{}`", slice),
129 format!("{}.swap({}, {})",
131 snippet(cx, idx1.span, ".."),
132 snippet(cx, idx2.span, "..")))
134 (false, String::new(), String::new())
136 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
137 (true, format!(" `{}` and `{}`", first, second),
138 format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
140 (true, String::new(), String::new())
143 let span = w[0].span.to(second.span);
145 span_lint_and_then(cx,
148 &format!("this looks like you are swapping{} manually", what),
150 if !sugg.is_empty() {
151 db.span_suggestion_with_applicability(
155 Applicability::Unspecified,
159 db.note("or maybe you should use `std::mem::replace`?");
168 /// Implementation of the `ALMOST_SWAPPED` lint.
169 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
170 for w in block.stmts.windows(2) {
172 if let StmtKind::Semi(ref first, _) = w[0].node;
173 if let StmtKind::Semi(ref second, _) = w[1].node;
174 if !differing_macro_contexts(first.span, second.span);
175 if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
176 if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
177 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
178 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
180 let lhs0 = Sugg::hir_opt(cx, lhs0);
181 let rhs0 = Sugg::hir_opt(cx, rhs0);
182 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
184 format!(" `{}` and `{}`", first, second),
185 first.mut_addr().to_string(),
186 second.mut_addr().to_string(),
189 (String::new(), String::new(), String::new())
192 let span = first.span.to(second.span);
194 span_lint_and_then(cx,
197 &format!("this looks like you are trying to swap{}", what),
199 if !what.is_empty() {
200 db.span_suggestion_with_applicability(
204 "std::mem::swap({}, {})",
208 Applicability::MaybeIncorrect,
210 db.note("or maybe you should use `std::mem::replace`?");