4 use syntax::codemap::mk_sp;
5 use utils::{differing_macro_contexts, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty, SpanlessEq};
8 /// **What it does:** Checks for manual swapping.
10 /// **Why is this bad?** The `std::mem::swap` function exposes the intent better
11 /// without deinitializing or copying either variable.
13 /// **Known problems:** None.
24 "manual swap of two variables"
27 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
29 /// **Why is this bad?** This looks like a failed attempt to swap.
31 /// **Known problems:** None.
41 "`foo = bar; bar = foo` sequence"
47 impl LintPass for Swap {
48 fn get_lints(&self) -> LintArray {
49 lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
53 impl LateLintPass for Swap {
54 fn check_block(&mut self, cx: &LateContext, block: &Block) {
55 check_manual_swap(cx, block);
56 check_suspicious_swap(cx, block);
60 /// Implementation of the `MANUAL_SWAP` lint.
61 fn check_manual_swap(cx: &LateContext, block: &Block) {
62 for w in block.stmts.windows(3) {
65 let StmtDecl(ref tmp, _) = w[0].node,
66 let DeclLocal(ref tmp) = tmp.node,
67 let Some(ref tmp_init) = tmp.init,
68 let PatKind::Binding(_, ref tmp_name, None) = tmp.pat.node,
71 let StmtSemi(ref first, _) = w[1].node,
72 let ExprAssign(ref lhs1, ref rhs1) = first.node,
75 let StmtSemi(ref second, _) = w[2].node,
76 let ExprAssign(ref lhs2, ref rhs2) = second.node,
77 let ExprPath(None, ref rhs2) = rhs2.node,
78 rhs2.segments.len() == 1,
80 tmp_name.node.as_str() == rhs2.segments[0].name.as_str(),
81 SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1),
82 SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2)
84 fn check_for_slice<'a>(cx: &LateContext, lhs1: &'a Expr, lhs2: &'a Expr) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
85 if let ExprIndex(ref lhs1, ref idx1) = lhs1.node {
86 if let ExprIndex(ref lhs2, ref idx2) = lhs2.node {
87 if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
88 let ty = walk_ptrs_ty(cx.tcx.expr_ty(lhs1));
90 if matches!(ty.sty, ty::TySlice(_)) ||
91 matches!(ty.sty, ty::TyArray(_, _)) ||
92 match_type(cx, ty, &paths::VEC) ||
93 match_type(cx, ty, &paths::VEC_DEQUE) {
94 return Some((lhs1, idx1, idx2));
103 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
104 if let Some(slice) = Sugg::hir_opt(cx, slice) {
106 format!(" elements of `{}`", slice),
107 format!("{}.swap({}, {})", slice.maybe_par(), snippet(cx, idx1.span, ".."), snippet(cx, idx2.span, "..")))
109 (false, "".to_owned(), "".to_owned())
112 if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
113 (true, format!(" `{}` and `{}`", first, second),
114 format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
116 (true, "".to_owned(), "".to_owned())
120 let span = mk_sp(w[0].span.lo, second.span.hi);
122 span_lint_and_then(cx,
125 &format!("this looks like you are swapping{} manually", what),
127 if !sugg.is_empty() {
128 db.span_suggestion(span, "try", sugg);
131 db.note("or maybe you should use `std::mem::replace`?");
139 /// Implementation of the `ALMOST_SWAPPED` lint.
140 fn check_suspicious_swap(cx: &LateContext, block: &Block) {
141 for w in block.stmts.windows(2) {
143 let StmtSemi(ref first, _) = w[0].node,
144 let StmtSemi(ref second, _) = w[1].node,
145 !differing_macro_contexts(first.span, second.span),
146 let ExprAssign(ref lhs0, ref rhs0) = first.node,
147 let ExprAssign(ref lhs1, ref rhs1) = second.node,
148 SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1),
149 SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0)
151 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs0), Sugg::hir_opt(cx, rhs0)) {
152 (format!(" `{}` and `{}`", first, second), first.mut_addr().to_string(), second.mut_addr().to_string())
154 ("".to_owned(), "".to_owned(), "".to_owned())
157 let span = mk_sp(first.span.lo, second.span.hi);
159 span_lint_and_then(cx,
162 &format!("this looks like you are trying to swap{}", what),
164 if !what.is_empty() {
165 db.span_suggestion(span, "try",
166 format!("std::mem::swap({}, {})", lhs, rhs));
167 db.note("or maybe you should use `std::mem::replace`?");