clippy_lints/src/eq_op.rs

   1 use crate::utils::{
   2     implements_trait, in_macro, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq,
   3 };
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{BinOp, BinOpKind, BorrowKind, Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8
   9 declare_clippy_lint! {
  10     /// **What it does:** Checks for equal operands to comparison, logical and
  11     /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  12     /// `||`, `&`, `|`, `^`, `-` and `/`).
  13     ///
  14     /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  15     ///
  16     /// **Known problems:** False negatives: We had some false positives regarding
  17     /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  18     /// of `x.pop() && x.pop()`), so we removed matching any function or method
  19     /// calls. We may introduce a whitelist of known pure functions in the future.
  20     ///
  21     /// **Example:**
  22     /// ```rust
  23     /// # let x = 1;
  24     /// if x + 1 == x + 1 {}
  25     /// ```
  26     pub EQ_OP,
  27     correctness,
  28     "equal operands on both sides of a comparison or bitwise combination (e.g., `x == x`)"
  29 }
  30
  31 declare_clippy_lint! {
  32     /// **What it does:** Checks for arguments to `==` which have their address
  33     /// taken to satisfy a bound
  34     /// and suggests to dereference the other argument instead
  35     ///
  36     /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  37     ///
  38     /// **Known problems:** None
  39     ///
  40     /// **Example:**
  41     /// ```ignore
  42     /// &x == y
  43     /// ```
  44     pub OP_REF,
  45     style,
  46     "taking a reference to satisfy the type constraints on `==`"
  47 }
  48
  49 declare_lint_pass!(EqOp => [EQ_OP, OP_REF]);
  50
  51 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  52     #[allow(clippy::similar_names, clippy::too_many_lines)]
  53     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
  54         if let ExprKind::Binary(op, ref left, ref right) = e.kind {
  55             if e.span.from_expansion() {
  56                 return;
  57             }
  58             let macro_with_not_op = |expr_kind: &ExprKind<'_>| {
  59                 if let ExprKind::Unary(_, ref expr) = *expr_kind {
  60                     in_macro(expr.span)
  61                 } else {
  62                     false
  63                 }
  64             };
  65             if macro_with_not_op(&left.kind) || macro_with_not_op(&right.kind) {
  66                 return;
  67             }
  68             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  69                 span_lint(
  70                     cx,
  71                     EQ_OP,
  72                     e.span,
  73                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  74                 );
  75                 return;
  76             }
  77             let (trait_id, requires_ref) = match op.node {
  78                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  79                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  80                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  81                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  82                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  83                 // don't lint short circuiting ops
  84                 BinOpKind::And | BinOpKind::Or => return,
  85                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  86                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  87                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  88                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  89                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  90                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  91                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  92                     (cx.tcx.lang_items().partial_ord_trait(), true)
  93                 },
  94             };
  95             if let Some(trait_id) = trait_id {
  96                 #[allow(clippy::match_same_arms)]
  97                 match (&left.kind, &right.kind) {
  98                     // do not suggest to dereference literals
  99                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 100                     // &foo == &bar
 101                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 102                         let lty = cx.tables.expr_ty(l);
 103                         let rty = cx.tables.expr_ty(r);
 104                         let lcpy = is_copy(cx, lty);
 105                         let rcpy = is_copy(cx, rty);
 106                         // either operator autorefs or both args are copyable
 107                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 108                             span_lint_and_then(
 109                                 cx,
 110                                 OP_REF,
 111                                 e.span,
 112                                 "needlessly taken reference of both operands",
 113                                 |diag| {
 114                                     let lsnip = snippet(cx, l.span, "...").to_string();
 115                                     let rsnip = snippet(cx, r.span, "...").to_string();
 116                                     multispan_sugg(
 117                                         diag,
 118                                         "use the values directly",
 119                                         vec![(left.span, lsnip), (right.span, rsnip)],
 120                                     );
 121                                 },
 122                             )
 123                         } else if lcpy
 124                             && !rcpy
 125                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 126                         {
 127                             span_lint_and_then(
 128                                 cx,
 129                                 OP_REF,
 130                                 e.span,
 131                                 "needlessly taken reference of left operand",
 132                                 |diag| {
 133                                     let lsnip = snippet(cx, l.span, "...").to_string();
 134                                     diag.span_suggestion(
 135                                         left.span,
 136                                         "use the left value directly",
 137                                         lsnip,
 138                                         Applicability::MaybeIncorrect, // FIXME #2597
 139                                     );
 140                                 },
 141                             )
 142                         } else if !lcpy
 143                             && rcpy
 144                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 145                         {
 146                             span_lint_and_then(
 147                                 cx,
 148                                 OP_REF,
 149                                 e.span,
 150                                 "needlessly taken reference of right operand",
 151                                 |diag| {
 152                                     let rsnip = snippet(cx, r.span, "...").to_string();
 153                                     diag.span_suggestion(
 154                                         right.span,
 155                                         "use the right value directly",
 156                                         rsnip,
 157                                         Applicability::MaybeIncorrect, // FIXME #2597
 158                                     );
 159                                 },
 160                             )
 161                         }
 162                     },
 163                     // &foo == bar
 164                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), _) => {
 165                         let lty = cx.tables.expr_ty(l);
 166                         let lcpy = is_copy(cx, lty);
 167                         if (requires_ref || lcpy)
 168                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 169                         {
 170                             span_lint_and_then(
 171                                 cx,
 172                                 OP_REF,
 173                                 e.span,
 174                                 "needlessly taken reference of left operand",
 175                                 |diag| {
 176                                     let lsnip = snippet(cx, l.span, "...").to_string();
 177                                     diag.span_suggestion(
 178                                         left.span,
 179                                         "use the left value directly",
 180                                         lsnip,
 181                                         Applicability::MaybeIncorrect, // FIXME #2597
 182                                     );
 183                                 },
 184                             )
 185                         }
 186                     },
 187                     // foo == &bar
 188                     (_, &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 189                         let rty = cx.tables.expr_ty(r);
 190                         let rcpy = is_copy(cx, rty);
 191                         if (requires_ref || rcpy)
 192                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 193                         {
 194                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |diag| {
 195                                 let rsnip = snippet(cx, r.span, "...").to_string();
 196                                 diag.span_suggestion(
 197                                     right.span,
 198                                     "use the right value directly",
 199                                     rsnip,
 200                                     Applicability::MaybeIncorrect, // FIXME #2597
 201                                 );
 202                             })
 203                         }
 204                     },
 205                     _ => {},
 206                 }
 207             }
 208         }
 209     }
 210 }
 211
 212 fn is_valid_operator(op: BinOp) -> bool {
 213     match op.node {
 214         BinOpKind::Sub
 215         | BinOpKind::Div
 216         | BinOpKind::Eq
 217         | BinOpKind::Lt
 218         | BinOpKind::Le
 219         | BinOpKind::Gt
 220         | BinOpKind::Ge
 221         | BinOpKind::Ne
 222         | BinOpKind::And
 223         | BinOpKind::Or
 224         | BinOpKind::BitXor
 225         | BinOpKind::BitAnd
 226         | BinOpKind::BitOr => true,
 227         _ => false,
 228     }
 229 }