clippy_lints/src/swap.rs

   1 use matches::matches;
   2 use crate::rustc::hir::*;
   3 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   4 use crate::rustc::{declare_tool_lint, lint_array};
   5 use if_chain::if_chain;
   6 use crate::rustc::ty;
   7 use crate::utils::{differing_macro_contexts, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty, SpanlessEq};
   8 use crate::utils::sugg::Sugg;
   9
  10 /// **What it does:** Checks for manual swapping.
  11 ///
  12 /// **Why is this bad?** The `std::mem::swap` function exposes the intent better
  13 /// without deinitializing or copying either variable.
  14 ///
  15 /// **Known problems:** None.
  16 ///
  17 /// **Example:**
  18 /// ```rust,ignore
  19 /// let t = b;
  20 /// b = a;
  21 /// a = t;
  22 /// ```
  23 /// Use std::mem::swap():
  24 /// ```rust
  25 /// std::mem::swap(&mut a, &mut b);
  26 /// ```
  27 declare_clippy_lint! {
  28     pub MANUAL_SWAP,
  29     complexity,
  30     "manual swap of two variables"
  31 }
  32
  33 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
  34 ///
  35 /// **Why is this bad?** This looks like a failed attempt to swap.
  36 ///
  37 /// **Known problems:** None.
  38 ///
  39 /// **Example:**
  40 /// ```rust,ignore
  41 /// a = b;
  42 /// b = a;
  43 /// ```
  44 declare_clippy_lint! {
  45     pub ALMOST_SWAPPED,
  46     correctness,
  47     "`foo = bar; bar = foo` sequence"
  48 }
  49
  50 #[derive(Copy, Clone)]
  51 pub struct Swap;
  52
  53 impl LintPass for Swap {
  54     fn get_lints(&self) -> LintArray {
  55         lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
  56     }
  57 }
  58
  59 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
  60     fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
  61         check_manual_swap(cx, block);
  62         check_suspicious_swap(cx, block);
  63     }
  64 }
  65
  66 /// Implementation of the `MANUAL_SWAP` lint.
  67 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
  68     for w in block.stmts.windows(3) {
  69         if_chain! {
  70             // let t = foo();
  71             if let StmtKind::Decl(ref tmp, _) = w[0].node;
  72             if let DeclKind::Local(ref tmp) = tmp.node;
  73             if let Some(ref tmp_init) = tmp.init;
  74             if let PatKind::Binding(_, _, ident, None) = tmp.pat.node;
  75
  76             // foo() = bar();
  77             if let StmtKind::Semi(ref first, _) = w[1].node;
  78             if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
  79
  80             // bar() = t;
  81             if let StmtKind::Semi(ref second, _) = w[2].node;
  82             if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
  83             if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
  84             if rhs2.segments.len() == 1;
  85
  86             if ident.as_str() == rhs2.segments[0].ident.as_str();
  87             if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
  88             if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
  89             then {
  90                 fn check_for_slice<'a>(
  91                     cx: &LateContext<'_, '_>,
  92                     lhs1: &'a Expr,
  93                     lhs2: &'a Expr,
  94                 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
  95                     if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
  96                         if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
  97                             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
  98                                 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
  99
 100                                 if matches!(ty.sty, ty::Slice(_)) ||
 101                                     matches!(ty.sty, ty::Array(_, _)) ||
 102                                     match_type(cx, ty, &paths::VEC) ||
 103                                     match_type(cx, ty, &paths::VEC_DEQUE) {
 104                                         return Some((lhs1, idx1, idx2));
 105                                 }
 106                             }
 107                         }
 108                     }
 109
 110                     None
 111                 }
 112
 113                 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
 114                     if let Some(slice) = Sugg::hir_opt(cx, slice) {
 115                         (false,
 116                          format!(" elements of `{}`", slice),
 117                          format!("{}.swap({}, {})",
 118                                  slice.maybe_par(),
 119                                  snippet(cx, idx1.span, ".."),
 120                                  snippet(cx, idx2.span, "..")))
 121                     } else {
 122                         (false, String::new(), String::new())
 123                     }
 124                 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
 125                     (true, format!(" `{}` and `{}`", first, second),
 126                         format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
 127                 } else {
 128                     (true, "".to_owned(), "".to_owned())
 129                 };
 130
 131                 let span = w[0].span.to(second.span);
 132
 133                 span_lint_and_then(cx,
 134                                    MANUAL_SWAP,
 135                                    span,
 136                                    &format!("this looks like you are swapping{} manually", what),
 137                                    |db| {
 138                                        if !sugg.is_empty() {
 139                                            db.span_suggestion(span, "try", sugg);
 140
 141                                            if replace {
 142                                                db.note("or maybe you should use `std::mem::replace`?");
 143                                            }
 144                                        }
 145                                    });
 146             }
 147         }
 148     }
 149 }
 150
 151 /// Implementation of the `ALMOST_SWAPPED` lint.
 152 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
 153     for w in block.stmts.windows(2) {
 154         if_chain! {
 155             if let StmtKind::Semi(ref first, _) = w[0].node;
 156             if let StmtKind::Semi(ref second, _) = w[1].node;
 157             if !differing_macro_contexts(first.span, second.span);
 158             if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
 159             if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
 160             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
 161             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
 162             then {
 163                 let lhs0 = Sugg::hir_opt(cx, lhs0);
 164                 let rhs0 = Sugg::hir_opt(cx, rhs0);
 165                 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
 166                     (
 167                         format!(" `{}` and `{}`", first, second),
 168                         first.mut_addr().to_string(),
 169                         second.mut_addr().to_string(),
 170                     )
 171                 } else {
 172                     (String::new(), String::new(), String::new())
 173                 };
 174
 175                 let span = first.span.to(second.span);
 176
 177                 span_lint_and_then(cx,
 178                                    ALMOST_SWAPPED,
 179                                    span,
 180                                    &format!("this looks like you are trying to swap{}", what),
 181                                    |db| {
 182                                        if !what.is_empty() {
 183                                            db.span_suggestion(span, "try",
 184                                                               format!("std::mem::swap({}, {})", lhs, rhs));
 185                                            db.note("or maybe you should use `std::mem::replace`?");
 186                                        }
 187                                    });
 188             }
 189         }
 190     }
 191 }