clippy_lints/src/eq_op.rs

   1 use rustc::hir::*;
   2 use rustc::lint::*;
   3 use utils::{implements_trait, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq};
   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
  27 /// taken to satisfy a bound
  28 /// and suggests to dereference the other argument instead
  29 ///
  30 /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  31 ///
  32 /// **Known problems:** None
  33 ///
  34 /// **Example:**
  35 /// ```rust
  36 /// &x == y
  37 /// ```
  38 declare_lint! {
  39     pub OP_REF,
  40     Warn,
  41     "taking a reference to satisfy the type constraints on `==`"
  42 }
  43
  44 #[derive(Copy, Clone)]
  45 pub struct EqOp;
  46
  47 impl LintPass for EqOp {
  48     fn get_lints(&self) -> LintArray {
  49         lint_array!(EQ_OP, OP_REF)
  50     }
  51 }
  52
  53 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  54     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  55         if let ExprBinary(ref op, ref left, ref right) = e.node {
  56             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  57                 span_lint(
  58                     cx,
  59                     EQ_OP,
  60                     e.span,
  61                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  62                 );
  63                 return;
  64             }
  65             let (trait_id, requires_ref) = match op.node {
  66                 BiAdd => (cx.tcx.lang_items.add_trait(), false),
  67                 BiSub => (cx.tcx.lang_items.sub_trait(), false),
  68                 BiMul => (cx.tcx.lang_items.mul_trait(), false),
  69                 BiDiv => (cx.tcx.lang_items.div_trait(), false),
  70                 BiRem => (cx.tcx.lang_items.rem_trait(), false),
  71                 // don't lint short circuiting ops
  72                 BiAnd | BiOr => return,
  73                 BiBitXor => (cx.tcx.lang_items.bitxor_trait(), false),
  74                 BiBitAnd => (cx.tcx.lang_items.bitand_trait(), false),
  75                 BiBitOr => (cx.tcx.lang_items.bitor_trait(), false),
  76                 BiShl => (cx.tcx.lang_items.shl_trait(), false),
  77                 BiShr => (cx.tcx.lang_items.shr_trait(), false),
  78                 BiNe | BiEq => (cx.tcx.lang_items.eq_trait(), true),
  79                 BiLt | BiLe | BiGe | BiGt => (cx.tcx.lang_items.ord_trait(), true),
  80             };
  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(..), _) | (_, &ExprLit(..)) => {},
  86                     // &foo == &bar
  87                     (&ExprAddrOf(_, ref l), &ExprAddrOf(_, ref r)) => {
  88                         let lty = cx.tables.expr_ty(l);
  89                         let rty = cx.tables.expr_ty(r);
  90                         let lcpy = is_copy(cx, lty);
  91                         let rcpy = is_copy(cx, rty);
  92                         // either operator autorefs or both args are copyable
  93                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty]) {
  94                             span_lint_and_then(
  95                                 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(
 103                                         db,
 104                                         "use the values directly".to_string(),
 105                                         vec![(left.span, lsnip), (right.span, rsnip)],
 106                                     );
 107                                 },
 108                             )
 109                         } else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)]) {
 110                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 111                                 let lsnip = snippet(cx, l.span, "...").to_string();
 112                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 113                             })
 114                         } else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty]) {
 115                             span_lint_and_then(
 116                                 cx,
 117                                 OP_REF,
 118                                 e.span,
 119                                 "needlessly taken reference of right operand",
 120                                 |db| {
 121                                     let rsnip = snippet(cx, r.span, "...").to_string();
 122                                     db.span_suggestion(right.span, "use the right value directly", rsnip);
 123                                 },
 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);
 131                         if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right)]) {
 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);
 142                         if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty]) {
 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(right.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 }