clippy_lints/src/eq_op.rs

   1 use crate::utils::{implements_trait, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq};
   2 use rustc::declare_lint_pass;
   3 use rustc::hir::*;
   4 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   5 use rustc_errors::Applicability;
   6 use rustc_session::declare_tool_lint;
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for equal operands to comparison, logical and
  10     /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  11     /// `||`, `&`, `|`, `^`, `-` and `/`).
  12     ///
  13     /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  14     ///
  15     /// **Known problems:** False negatives: We had some false positives regarding
  16     /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  17     /// of `x.pop() && x.pop()`), so we removed matching any function or method
  18     /// calls. We may introduce a whitelist of known pure functions in the future.
  19     ///
  20     /// **Example:**
  21     /// ```rust
  22     /// # let x = 1;
  23     /// if x + 1 == x + 1 {}
  24     /// ```
  25     pub EQ_OP,
  26     correctness,
  27     "equal operands on both sides of a comparison or bitwise combination (e.g., `x == x`)"
  28 }
  29
  30 declare_clippy_lint! {
  31     /// **What it does:** Checks for arguments to `==` which have their address
  32     /// taken to satisfy a bound
  33     /// and suggests to dereference the other argument instead
  34     ///
  35     /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  36     ///
  37     /// **Known problems:** None
  38     ///
  39     /// **Example:**
  40     /// ```ignore
  41     /// &x == y
  42     /// ```
  43     pub OP_REF,
  44     style,
  45     "taking a reference to satisfy the type constraints on `==`"
  46 }
  47
  48 declare_lint_pass!(EqOp => [EQ_OP, OP_REF]);
  49
  50 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  51     #[allow(clippy::similar_names, clippy::too_many_lines)]
  52     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
  53         if let ExprKind::Binary(op, ref left, ref right) = e.kind {
  54             if e.span.from_expansion() {
  55                 return;
  56             }
  57             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  58                 span_lint(
  59                     cx,
  60                     EQ_OP,
  61                     e.span,
  62                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  63                 );
  64                 return;
  65             }
  66             let (trait_id, requires_ref) = match op.node {
  67                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  68                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  69                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  70                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  71                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  72                 // don't lint short circuiting ops
  73                 BinOpKind::And | BinOpKind::Or => return,
  74                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  75                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  76                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  77                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  78                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  79                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  80                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  81                     (cx.tcx.lang_items().partial_ord_trait(), true)
  82                 },
  83             };
  84             if let Some(trait_id) = trait_id {
  85                 #[allow(clippy::match_same_arms)]
  86                 match (&left.kind, &right.kind) {
  87                     // do not suggest to dereference literals
  88                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
  89                     // &foo == &bar
  90                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), &ExprKind::AddrOf(BorrowKind::Ref, _, 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
 113                             && !rcpy
 114                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 115                         {
 116                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 117                                 let lsnip = snippet(cx, l.span, "...").to_string();
 118                                 db.span_suggestion(
 119                                     left.span,
 120                                     "use the left value directly",
 121                                     lsnip,
 122                                     Applicability::MaybeIncorrect, // FIXME #2597
 123                                 );
 124                             })
 125                         } else if !lcpy
 126                             && rcpy
 127                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 128                         {
 129                             span_lint_and_then(
 130                                 cx,
 131                                 OP_REF,
 132                                 e.span,
 133                                 "needlessly taken reference of right operand",
 134                                 |db| {
 135                                     let rsnip = snippet(cx, r.span, "...").to_string();
 136                                     db.span_suggestion(
 137                                         right.span,
 138                                         "use the right value directly",
 139                                         rsnip,
 140                                         Applicability::MaybeIncorrect, // FIXME #2597
 141                                     );
 142                                 },
 143                             )
 144                         }
 145                     },
 146                     // &foo == bar
 147                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), _) => {
 148                         let lty = cx.tables.expr_ty(l);
 149                         let lcpy = is_copy(cx, lty);
 150                         if (requires_ref || lcpy)
 151                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 152                         {
 153                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 154                                 let lsnip = snippet(cx, l.span, "...").to_string();
 155                                 db.span_suggestion(
 156                                     left.span,
 157                                     "use the left value directly",
 158                                     lsnip,
 159                                     Applicability::MaybeIncorrect, // FIXME #2597
 160                                 );
 161                             })
 162                         }
 163                     },
 164                     // foo == &bar
 165                     (_, &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 166                         let rty = cx.tables.expr_ty(r);
 167                         let rcpy = is_copy(cx, rty);
 168                         if (requires_ref || rcpy)
 169                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 170                         {
 171                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 172                                 let rsnip = snippet(cx, r.span, "...").to_string();
 173                                 db.span_suggestion(
 174                                     right.span,
 175                                     "use the right value directly",
 176                                     rsnip,
 177                                     Applicability::MaybeIncorrect, // FIXME #2597
 178                                 );
 179                             })
 180                         }
 181                     },
 182                     _ => {},
 183                 }
 184             }
 185         }
 186     }
 187 }
 188
 189 fn is_valid_operator(op: BinOp) -> bool {
 190     match op.node {
 191         BinOpKind::Sub
 192         | BinOpKind::Div
 193         | BinOpKind::Eq
 194         | BinOpKind::Lt
 195         | BinOpKind::Le
 196         | BinOpKind::Gt
 197         | BinOpKind::Ge
 198         | BinOpKind::Ne
 199         | BinOpKind::And
 200         | BinOpKind::Or
 201         | BinOpKind::BitXor
 202         | BinOpKind::BitAnd
 203         | BinOpKind::BitOr => true,
 204         _ => false,
 205     }
 206 }