clippy_lints/src/eq_op.rs

   1 use rustc::hir::*;
   2 use rustc::lint::*;
   3 use crate::utils::{in_macro, 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_clippy_lint! {
  21     pub EQ_OP,
  22     correctness,
  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_clippy_lint! {
  39     pub OP_REF,
  40     style,
  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 ExprKind::Binary(op, ref left, ref right) = e.node {
  56             if in_macro(e.span) {
  57                 return;
  58             }
  59             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  60                 span_lint(
  61                     cx,
  62                     EQ_OP,
  63                     e.span,
  64                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  65                 );
  66                 return;
  67             }
  68             let (trait_id, requires_ref) = match op.node {
  69                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  70                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  71                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  72                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  73                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  74                 // don't lint short circuiting ops
  75                 BinOpKind::And | BinOpKind::Or => return,
  76                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  77                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  78                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  79                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  80                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  81                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  82                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => (cx.tcx.lang_items().ord_trait(), true),
  83             };
  84             if let Some(trait_id) = trait_id {
  85                 #[allow(match_same_arms)]
  86                 match (&left.node, &right.node) {
  87                     // do not suggest to dereference literals
  88                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
  89                     // &foo == &bar
  90                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
  91                         let lty = cx.tables.expr_ty(l);
  92                         let rty = cx.tables.expr_ty(r);
  93                         let lcpy = is_copy(cx, lty);
  94                         let rcpy = is_copy(cx, rty);
  95                         // either operator autorefs or both args are copyable
  96                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
  97                             span_lint_and_then(
  98                                 cx,
  99                                 OP_REF,
 100                                 e.span,
 101                                 "needlessly taken reference of both operands",
 102                                 |db| {
 103                                     let lsnip = snippet(cx, l.span, "...").to_string();
 104                                     let rsnip = snippet(cx, r.span, "...").to_string();
 105                                     multispan_sugg(
 106                                         db,
 107                                         "use the values directly".to_string(),
 108                                         vec![(left.span, lsnip), (right.span, rsnip)],
 109                                     );
 110                                 },
 111                             )
 112                         } else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 113                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 114                                 let lsnip = snippet(cx, l.span, "...").to_string();
 115                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 116                             })
 117                         } else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 118                             span_lint_and_then(
 119                                 cx,
 120                                 OP_REF,
 121                                 e.span,
 122                                 "needlessly taken reference of right operand",
 123                                 |db| {
 124                                     let rsnip = snippet(cx, r.span, "...").to_string();
 125                                     db.span_suggestion(right.span, "use the right value directly", rsnip);
 126                                 },
 127                             )
 128                         }
 129                     },
 130                     // &foo == bar
 131                     (&ExprKind::AddrOf(_, ref l), _) => {
 132                         let lty = cx.tables.expr_ty(l);
 133                         let lcpy = is_copy(cx, lty);
 134                         if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 135                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 136                                 let lsnip = snippet(cx, l.span, "...").to_string();
 137                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 138                             })
 139                         }
 140                     },
 141                     // foo == &bar
 142                     (_, &ExprKind::AddrOf(_, ref r)) => {
 143                         let rty = cx.tables.expr_ty(r);
 144                         let rcpy = is_copy(cx, rty);
 145                         if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 146                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 147                                 let rsnip = snippet(cx, r.span, "...").to_string();
 148                                 db.span_suggestion(right.span, "use the right value directly", rsnip);
 149                             })
 150                         }
 151                     },
 152                     _ => {},
 153                 }
 154             }
 155         }
 156     }
 157 }
 158
 159
 160 fn is_valid_operator(op: BinOp) -> bool {
 161     match op.node {
 162         BinOpKind::Sub | BinOpKind::Div | BinOpKind::Eq | BinOpKind::Lt | BinOpKind::Le | BinOpKind::Gt | BinOpKind::Ge | BinOpKind::Ne | BinOpKind::And | BinOpKind::Or | BinOpKind::BitXor | BinOpKind::BitAnd | BinOpKind::BitOr => true,
 163         _ => false,
 164     }
 165 }