clippy_lints/src/eq_op.rs

   1 use rustc::hir::*;
   2 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   3 use rustc::{declare_tool_lint, lint_array};
   4 use crate::utils::{in_macro, implements_trait, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq};
   5
   6 /// **What it does:** Checks for equal operands to comparison, logical and
   7 /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
   8 /// `||`, `&`, `|`, `^`, `-` and `/`).
   9 ///
  10 /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  11 ///
  12 /// **Known problems:** False negatives: We had some false positives regarding
  13 /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  14 /// of `x.pop() && x.pop()`), so we removed matching any function or method
  15 /// calls. We may introduce a whitelist of known pure functions in the future.
  16 ///
  17 /// **Example:**
  18 /// ```rust
  19 /// x + 1 == x + 1
  20 /// ```
  21 declare_clippy_lint! {
  22     pub EQ_OP,
  23     correctness,
  24     "equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)"
  25 }
  26
  27 /// **What it does:** Checks for arguments to `==` which have their address
  28 /// taken to satisfy a bound
  29 /// and suggests to dereference the other argument instead
  30 ///
  31 /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  32 ///
  33 /// **Known problems:** None
  34 ///
  35 /// **Example:**
  36 /// ```rust
  37 /// &x == y
  38 /// ```
  39 declare_clippy_lint! {
  40     pub OP_REF,
  41     style,
  42     "taking a reference to satisfy the type constraints on `==`"
  43 }
  44
  45 #[derive(Copy, Clone)]
  46 pub struct EqOp;
  47
  48 impl LintPass for EqOp {
  49     fn get_lints(&self) -> LintArray {
  50         lint_array!(EQ_OP, OP_REF)
  51     }
  52 }
  53
  54 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  55     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  56         if let ExprKind::Binary(op, ref left, ref right) = e.node {
  57             if in_macro(e.span) {
  58                 return;
  59             }
  60             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  61                 span_lint(
  62                     cx,
  63                     EQ_OP,
  64                     e.span,
  65                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  66                 );
  67                 return;
  68             }
  69             let (trait_id, requires_ref) = match op.node {
  70                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  71                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  72                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  73                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  74                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  75                 // don't lint short circuiting ops
  76                 BinOpKind::And | BinOpKind::Or => return,
  77                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  78                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  79                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  80                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  81                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  82                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  83                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => (cx.tcx.lang_items().ord_trait(), true),
  84             };
  85             if let Some(trait_id) = trait_id {
  86                 #[allow(clippy::match_same_arms)]
  87                 match (&left.node, &right.node) {
  88                     // do not suggest to dereference literals
  89                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
  90                     // &foo == &bar
  91                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
  92                         let lty = cx.tables.expr_ty(l);
  93                         let rty = cx.tables.expr_ty(r);
  94                         let lcpy = is_copy(cx, lty);
  95                         let rcpy = is_copy(cx, rty);
  96                         // either operator autorefs or both args are copyable
  97                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
  98                             span_lint_and_then(
  99                                 cx,
 100                                 OP_REF,
 101                                 e.span,
 102                                 "needlessly taken reference of both operands",
 103                                 |db| {
 104                                     let lsnip = snippet(cx, l.span, "...").to_string();
 105                                     let rsnip = snippet(cx, r.span, "...").to_string();
 106                                     multispan_sugg(
 107                                         db,
 108                                         "use the values directly".to_string(),
 109                                         vec![(left.span, lsnip), (right.span, rsnip)],
 110                                     );
 111                                 },
 112                             )
 113                         } else if lcpy && !rcpy && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 114                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 115                                 let lsnip = snippet(cx, l.span, "...").to_string();
 116                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 117                             })
 118                         } else if !lcpy && rcpy && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 119                             span_lint_and_then(
 120                                 cx,
 121                                 OP_REF,
 122                                 e.span,
 123                                 "needlessly taken reference of right operand",
 124                                 |db| {
 125                                     let rsnip = snippet(cx, r.span, "...").to_string();
 126                                     db.span_suggestion(right.span, "use the right value directly", rsnip);
 127                                 },
 128                             )
 129                         }
 130                     },
 131                     // &foo == bar
 132                     (&ExprKind::AddrOf(_, ref l), _) => {
 133                         let lty = cx.tables.expr_ty(l);
 134                         let lcpy = is_copy(cx, lty);
 135                         if (requires_ref || lcpy) && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()]) {
 136                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 137                                 let lsnip = snippet(cx, l.span, "...").to_string();
 138                                 db.span_suggestion(left.span, "use the left value directly", lsnip);
 139                             })
 140                         }
 141                     },
 142                     // foo == &bar
 143                     (_, &ExprKind::AddrOf(_, ref r)) => {
 144                         let rty = cx.tables.expr_ty(r);
 145                         let rcpy = is_copy(cx, rty);
 146                         if (requires_ref || rcpy) && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()]) {
 147                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 148                                 let rsnip = snippet(cx, r.span, "...").to_string();
 149                                 db.span_suggestion(right.span, "use the right value directly", rsnip);
 150                             })
 151                         }
 152                     },
 153                     _ => {},
 154                 }
 155             }
 156         }
 157     }
 158 }
 159
 160
 161 fn is_valid_operator(op: BinOp) -> bool {
 162     match op.node {
 163         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,
 164         _ => false,
 165     }
 166 }