clippy_lints/src/swap.rs

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