clippy_lints/src/eq_op.rs

   1 use rustc::hir::*;
   2 use rustc::lint::*;
   3 use utils::{SpanlessEq, span_lint, span_lint_and_then, multispan_sugg, snippet, implements_trait, is_copy};
   4
   5 /// **What it does:** Checks for equal operands to comparison, logical and
   6 /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
   7 /// `||`, `&`, `|`, `^`, `-` and `/`).
   8 ///
   9 /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  10 ///
  11 /// **Known problems:** False negatives: We had some false positives regarding
  12 /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  13 /// of `x.pop() && x.pop()`), so we removed matching any function or method
  14 /// calls. We may introduce a whitelist of known pure functions in the future.
  15 ///
  16 /// **Example:**
  17 /// ```rust
  18 /// x + 1 == x + 1
  19 /// ```
  20 declare_lint! {
  21     pub EQ_OP,
  22     Warn,
  23     "equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)"
  24 }
  25
  26 /// **What it does:** Checks for arguments to `==` which have their address taken to satisfy a bound
  27 /// and suggests to dereference the other argument instead
  28 ///
  29 /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  30 ///
  31 /// **Known problems:** None
  32 ///
  33 /// **Example:**
  34 /// ```rust
  35 /// &x == y
  36 /// ```
  37 declare_lint! {
  38     pub OP_REF,
  39     Warn,
  40     "taking a reference to satisfy the type constraints on `==`"
  41 }
  42
  43 #[derive(Copy,Clone)]
  44 pub struct EqOp;
  45
  46 impl LintPass for EqOp {
  47     fn get_lints(&self) -> LintArray {
  48         lint_array!(EQ_OP, OP_REF)
  49     }
  50 }
  51
  52 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  53     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  54         if let ExprBinary(ref op, ref left, ref right) = e.node {
  55             if is_valid_operator(op) {
  56                 if SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  57                     span_lint(cx,
  58                               EQ_OP,
  59                               e.span,
  60                               &format!("equal expressions as operands to `{}`", op.node.as_str()));
  61                     return;
  62                 }
  63             }
  64             let (trait_id, requires_ref) = match op.node {
  65                 BiAdd => (cx.tcx.lang_items.add_trait(), false),
  66                 BiSub => (cx.tcx.lang_items.sub_trait(), false),
  67                 BiMul => (cx.tcx.lang_items.mul_trait(), false),
  68                 BiDiv => (cx.tcx.lang_items.div_trait(), false),
  69                 BiRem => (cx.tcx.lang_items.rem_trait(), false),
  70                 // don't lint short circuiting ops
  71                 BiAnd | BiOr => return,
  72                 BiBitXor => (cx.tcx.lang_items.bitxor_trait(), false),
  73                 BiBitAnd => (cx.tcx.lang_items.bitand_trait(), false),
  74                 BiBitOr => (cx.tcx.lang_items.bitor_trait(), false),
  75                 BiShl => (cx.tcx.lang_items.shl_trait(), false),
  76                 BiShr => (cx.tcx.lang_items.shr_trait(), false),
  77                 BiNe | BiEq => (cx.tcx.lang_items.eq_trait(), true),
  78                 BiLt | BiLe | BiGe | BiGt => (cx.tcx.lang_items.ord_trait(), true),
  79             };
  80             let parent = cx.tcx.hir.get_parent(e.id);
  81             if let Some(trait_id) = trait_id {
  82                 #[allow(match_same_arms)]
  83                 match (&left.node, &right.node) {
  84                     // do not suggest to dereference literals
  85                     (&ExprLit(..), _) |
  86                     (_, &ExprLit(..)) => {},
  87                     // &foo == &bar
  88                     (&ExprAddrOf(_, ref l), &ExprAddrOf(_, ref r)) => {
  89                         let lty = cx.tables.expr_ty(l);
  90                         let rty = cx.tables.expr_ty(r);
  91                         let lcpy = is_copy(cx, lty, parent);
  92                         let rcpy = is_copy(cx, rty, parent);
  93                         // either operator autorefs or both args are copyable
  94                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty], None) {
  95                             span_lint_and_then(cx,
  96                                                 OP_REF,
  97                                                 e.span,
  98                                                 "needlessly taken reference of both operands",
  99                                                 |db| {
 100                                 let lsnip = snippet(cx, l.span, "...").to_string();
 101                                 let rsnip = snippet(cx, r.span, "...").to_string();
 102                                 multispan_sugg(db,
 103                                                 "use the values directly".to_string(),
 104                                                 vec![(left.span, lsnip),
 105                                                     (right.span, rsnip)]);
 106                             })
 107                         } else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)], None) {
 108                             span_lint_and_then(cx,
 109                                                 OP_REF,
 110                                                 e.span,
 111                                                 "needlessly taken reference of left operand",
 112                                                 |db| {
 113                                 let lsnip = snippet(cx, l.span, "...").to_string();
 114                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 115                             })
 116                         } else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty], None) {
 117                             span_lint_and_then(cx,
 118                                                 OP_REF,
 119                                                 e.span,
 120                                                 "needlessly taken reference of right operand",
 121                                                 |db| {
 122                                 let rsnip = snippet(cx, r.span, "...").to_string();
 123                                 db.span_suggestion(right.span, "use the right value directly", rsnip);
 124                             })
 125                         }
 126                     },
 127                     // &foo == bar
 128                     (&ExprAddrOf(_, ref l), _) => {
 129                         let lty = cx.tables.expr_ty(l);
 130                         let lcpy = is_copy(cx, lty, parent);
 131                         if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)], None) {
 132                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 133                                 let lsnip = snippet(cx, l.span, "...").to_string();
 134                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 135                             })
 136                         }
 137                     },
 138                     // foo == &bar
 139                     (_, &ExprAddrOf(_, ref r)) => {
 140                         let rty = cx.tables.expr_ty(r);
 141                         let rcpy = is_copy(cx, rty, parent);
 142                         if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty], None) {
 143                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 144                                 let rsnip = snippet(cx, r.span, "...").to_string();
 145                                 db.span_suggestion(left.span, "use the right value directly", rsnip);
 146                             })
 147                         }
 148                     },
 149                     _ => {},
 150                 }
 151             }
 152         }
 153     }
 154 }
 155
 156
 157 fn is_valid_operator(op: &BinOp) -> bool {
 158     match op.node {
 159         BiSub | BiDiv | BiEq | BiLt | BiLe | BiGt | BiGe | BiNe | BiAnd | BiOr | BiBitXor | BiBitAnd | BiBitOr => true,
 160         _ => false,
 161     }
 162 }