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 use crate::rustc_errors::Applicability;
  10
  11 /// **What it does:** Checks for manual swapping.
  12 ///
  13 /// **Why is this bad?** The `std::mem::swap` function exposes the intent better
  14 /// without deinitializing or copying either variable.
  15 ///
  16 /// **Known problems:** None.
  17 ///
  18 /// **Example:**
  19 /// ```rust,ignore
  20 /// let t = b;
  21 /// b = a;
  22 /// a = t;
  23 /// ```
  24 /// Use std::mem::swap():
  25 /// ```rust
  26 /// std::mem::swap(&mut a, &mut b);
  27 /// ```
  28 declare_clippy_lint! {
  29     pub MANUAL_SWAP,
  30     complexity,
  31     "manual swap of two variables"
  32 }
  33
  34 /// **What it does:** Checks for `foo = bar; bar = foo` sequences.
  35 ///
  36 /// **Why is this bad?** This looks like a failed attempt to swap.
  37 ///
  38 /// **Known problems:** None.
  39 ///
  40 /// **Example:**
  41 /// ```rust,ignore
  42 /// a = b;
  43 /// b = a;
  44 /// ```
  45 declare_clippy_lint! {
  46     pub ALMOST_SWAPPED,
  47     correctness,
  48     "`foo = bar; bar = foo` sequence"
  49 }
  50
  51 #[derive(Copy, Clone)]
  52 pub struct Swap;
  53
  54 impl LintPass for Swap {
  55     fn get_lints(&self) -> LintArray {
  56         lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
  57     }
  58 }
  59
  60 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
  61     fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
  62         check_manual_swap(cx, block);
  63         check_suspicious_swap(cx, block);
  64     }
  65 }
  66
  67 /// Implementation of the `MANUAL_SWAP` lint.
  68 fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block) {
  69     for w in block.stmts.windows(3) {
  70         if_chain! {
  71             // let t = foo();
  72             if let StmtKind::Decl(ref tmp, _) = w[0].node;
  73             if let DeclKind::Local(ref tmp) = tmp.node;
  74             if let Some(ref tmp_init) = tmp.init;
  75             if let PatKind::Binding(_, _, ident, None) = tmp.pat.node;
  76
  77             // foo() = bar();
  78             if let StmtKind::Semi(ref first, _) = w[1].node;
  79             if let ExprKind::Assign(ref lhs1, ref rhs1) = first.node;
  80
  81             // bar() = t;
  82             if let StmtKind::Semi(ref second, _) = w[2].node;
  83             if let ExprKind::Assign(ref lhs2, ref rhs2) = second.node;
  84             if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.node;
  85             if rhs2.segments.len() == 1;
  86
  87             if ident.as_str() == rhs2.segments[0].ident.as_str();
  88             if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
  89             if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
  90             then {
  91                 fn check_for_slice<'a>(
  92                     cx: &LateContext<'_, '_>,
  93                     lhs1: &'a Expr,
  94                     lhs2: &'a Expr,
  95                 ) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
  96                     if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.node {
  97                         if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.node {
  98                             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
  99                                 let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
 100
 101                                 if matches!(ty.sty, ty::Slice(_)) ||
 102                                     matches!(ty.sty, ty::Array(_, _)) ||
 103                                     match_type(cx, ty, &paths::VEC) ||
 104                                     match_type(cx, ty, &paths::VEC_DEQUE) {
 105                                         return Some((lhs1, idx1, idx2));
 106                                 }
 107                             }
 108                         }
 109                     }
 110
 111                     None
 112                 }
 113
 114                 let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
 115                     if let Some(slice) = Sugg::hir_opt(cx, slice) {
 116                         (false,
 117                          format!(" elements of `{}`", slice),
 118                          format!("{}.swap({}, {})",
 119                                  slice.maybe_par(),
 120                                  snippet(cx, idx1.span, ".."),
 121                                  snippet(cx, idx2.span, "..")))
 122                     } else {
 123                         (false, String::new(), String::new())
 124                     }
 125                 } else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
 126                     (true, format!(" `{}` and `{}`", first, second),
 127                         format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
 128                 } else {
 129                     (true, String::new(), String::new())
 130                 };
 131
 132                 let span = w[0].span.to(second.span);
 133
 134                 span_lint_and_then(cx,
 135                                    MANUAL_SWAP,
 136                                    span,
 137                                    &format!("this looks like you are swapping{} manually", what),
 138                                    |db| {
 139                                        if !sugg.is_empty() {
 140                                            db.span_suggestion_with_applicability(
 141                                                         span,
 142                                                         "try",
 143                                                         sugg,
 144                                                         Applicability::Unspecified,
 145                                                         );
 146
 147                                            if replace {
 148                                                db.note("or maybe you should use `std::mem::replace`?");
 149                                            }
 150                                        }
 151                                    });
 152             }
 153         }
 154     }
 155 }
 156
 157 /// Implementation of the `ALMOST_SWAPPED` lint.
 158 fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block) {
 159     for w in block.stmts.windows(2) {
 160         if_chain! {
 161             if let StmtKind::Semi(ref first, _) = w[0].node;
 162             if let StmtKind::Semi(ref second, _) = w[1].node;
 163             if !differing_macro_contexts(first.span, second.span);
 164             if let ExprKind::Assign(ref lhs0, ref rhs0) = first.node;
 165             if let ExprKind::Assign(ref lhs1, ref rhs1) = second.node;
 166             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
 167             if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
 168             then {
 169                 let lhs0 = Sugg::hir_opt(cx, lhs0);
 170                 let rhs0 = Sugg::hir_opt(cx, rhs0);
 171                 let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
 172                     (
 173                         format!(" `{}` and `{}`", first, second),
 174                         first.mut_addr().to_string(),
 175                         second.mut_addr().to_string(),
 176                     )
 177                 } else {
 178                     (String::new(), String::new(), String::new())
 179                 };
 180
 181                 let span = first.span.to(second.span);
 182
 183                 span_lint_and_then(cx,
 184                                    ALMOST_SWAPPED,
 185                                    span,
 186                                    &format!("this looks like you are trying to swap{}", what),
 187                                    |db| {
 188                                        if !what.is_empty() {
 189                                            db.span_suggestion_with_applicability(
 190                                                               span,
 191                                                               "try",
 192                                                               format!("std::mem::swap({}, {})",
 193                                                                     lhs,
 194                                                                     rhs),
 195                                                               Applicability::Unspecified,
 196                                                               );
 197                                            db.note("or maybe you should use `std::mem::replace`?");
 198                                        }
 199                                    });
 200             }
 201         }
 202     }
 203 }