clippy_lints/src/swap.rs

   1 use matches::matches;
   2 use rustc::hir::*;
   3 use rustc::lint::*;
   4 use rustc::{declare_lint, lint_array};
   5 use if_chain::if_chain;
   6 use 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 declare_clippy_lint! {
  24     pub MANUAL_SWAP,
  25     complexity,
  26     "manual swap of two variables"
  27 }
  28
  29 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
  30 ///
  31 /// **Why is this bad?** This looks like a failed attempt to swap.
  32 ///
  33 /// **Known problems:** None.
  34 ///
  35 /// **Example:**
  36 /// ```rust,ignore
  37 /// a = b;
  38 /// b = a;
  39 /// ```
  40 declare_clippy_lint! {
  41     pub ALMOST_SWAPPED,
  42     correctness,
  43     "`foo = bar; bar = foo` sequence"
  44 }
  45
  46 #[derive(Copy, Clone)]
  47 pub struct Swap;
  48
  49 impl LintPass for Swap {
  50     fn get_lints(&self) -> LintArray {
  51         lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
  52     }
  53 }
  54
  55 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
  56     fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
  57         check_manual_swap(cx, block);
  58         check_suspicious_swap(cx, block);
  59     }
  60 }
  61
  62 /// Implementation of the `MANUAL_SWAP` lint.
  63 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
  64     for w in block.stmts.windows(3) {
  65         if_chain! {
  66             // let t = foo();
  67             if let StmtKind::Decl(ref tmp, _) = w[0].node;
  68             if let DeclKind::Local(ref tmp) = tmp.node;
  69             if let Some(ref tmp_init) = tmp.init;
  70             if let PatKind::Binding(_, _, ident, None) = tmp.pat.node;
  71
  72             // foo() = bar();
  73             if let StmtKind::Semi(ref first, _) = w[1].node;
  74             if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
  75
  76             // bar() = t;
  77             if let StmtKind::Semi(ref second, _) = w[2].node;
  78             if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
  79             if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
  80             if rhs2.segments.len() == 1;
  81
  82             if ident.as_str() == rhs2.segments[0].ident.as_str();
  83             if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
  84             if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
  85             then {
  86                 fn check_for_slice<'a>(
  87                     cx: &LateContext<'_, '_>,
  88                     lhs1: &'a Expr,
  89                     lhs2: &'a Expr,
  90                 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
  91                     if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
  92                         if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
  93                             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
  94                                 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
  95
  96                                 if matches!(ty.sty, ty::TySlice(_)) ||
  97                                     matches!(ty.sty, ty::TyArray(_, _)) ||
  98                                     match_type(cx, ty, &paths::VEC) ||
  99                                     match_type(cx, ty, &paths::VEC_DEQUE) {
 100                                         return Some((lhs1, idx1, idx2));
 101                                 }
 102                             }
 103                         }
 104                     }
 105
 106                     None
 107                 }
 108
 109                 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
 110                     if let Some(slice) = Sugg::hir_opt(cx, slice) {
 111                         (false,
 112                          format!(" elements of `{}`", slice),
 113                          format!("{}.swap({}, {})",
 114                                  slice.maybe_par(),
 115                                  snippet(cx, idx1.span, ".."),
 116                                  snippet(cx, idx2.span, "..")))
 117                     } else {
 118                         (false, "".to_owned(), "".to_owned())
 119                     }
 120                 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
 121                     (true, format!(" `{}` and `{}`", first, second),
 122                         format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
 123                 } else {
 124                     (true, "".to_owned(), "".to_owned())
 125                 };
 126
 127                 let span = w[0].span.to(second.span);
 128
 129                 span_lint_and_then(cx,
 130                                    MANUAL_SWAP,
 131                                    span,
 132                                    &format!("this looks like you are swapping{} manually", what),
 133                                    |db| {
 134                                        if !sugg.is_empty() {
 135                                            db.span_suggestion(span, "try", sugg);
 136
 137                                            if replace {
 138                                                db.note("or maybe you should use `std::mem::replace`?");
 139                                            }
 140                                        }
 141                                    });
 142             }
 143         }
 144     }
 145 }
 146
 147 /// Implementation of the `ALMOST_SWAPPED` lint.
 148 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
 149     for w in block.stmts.windows(2) {
 150         if_chain! {
 151             if let StmtKind::Semi(ref first, _) = w[0].node;
 152             if let StmtKind::Semi(ref second, _) = w[1].node;
 153             if !differing_macro_contexts(first.span, second.span);
 154             if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
 155             if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
 156             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
 157             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
 158             then {
 159                 let lhs0 = Sugg::hir_opt(cx, lhs0);
 160                 let rhs0 = Sugg::hir_opt(cx, rhs0);
 161                 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
 162                     (
 163                         format!(" `{}` and `{}`", first, second),
 164                         first.mut_addr().to_string(),
 165                         second.mut_addr().to_string(),
 166                     )
 167                 } else {
 168                     ("".to_owned(), "".to_owned(), "".to_owned())
 169                 };
 170
 171                 let span = first.span.to(second.span);
 172
 173                 span_lint_and_then(cx,
 174                                    ALMOST_SWAPPED,
 175                                    span,
 176                                    &format!("this looks like you are trying to swap{}", what),
 177                                    |db| {
 178                                        if !what.is_empty() {
 179                                            db.span_suggestion(span, "try",
 180                                                               format!("std::mem::swap({}, {})", lhs, rhs));
 181                                            db.note("or maybe you should use `std::mem::replace`?");
 182                                        }
 183                                    });
 184             }
 185         }
 186     }
 187 }