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