src/tools/clippy/clippy_lints/src/eq_op.rs

   1 use crate::utils::{
   2     eq_expr_value, implements_trait, in_macro, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then,
   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 list 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     /// // Bad
  43     /// &x == y
  44     ///
  45     /// // Good
  46     /// x == *y
  47     /// ```
  48     pub OP_REF,
  49     style,
  50     "taking a reference to satisfy the type constraints on `==`"
  51 }
  52
  53 declare_lint_pass!(EqOp => [EQ_OP, OP_REF]);
  54
  55 impl<'tcx> LateLintPass<'tcx> for EqOp {
  56     #[allow(clippy::similar_names, clippy::too_many_lines)]
  57     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  58         if let ExprKind::Binary(op, ref left, ref right) = e.kind {
  59             if e.span.from_expansion() {
  60                 return;
  61             }
  62             let macro_with_not_op = |expr_kind: &ExprKind<'_>| {
  63                 if let ExprKind::Unary(_, ref expr) = *expr_kind {
  64                     in_macro(expr.span)
  65                 } else {
  66                     false
  67                 }
  68             };
  69             if macro_with_not_op(&left.kind) || macro_with_not_op(&right.kind) {
  70                 return;
  71             }
  72             if is_valid_operator(op) && eq_expr_value(cx, left, right) {
  73                 span_lint(
  74                     cx,
  75                     EQ_OP,
  76                     e.span,
  77                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  78                 );
  79                 return;
  80             }
  81             let (trait_id, requires_ref) = match op.node {
  82                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  83                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  84                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  85                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  86                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  87                 // don't lint short circuiting ops
  88                 BinOpKind::And | BinOpKind::Or => return,
  89                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  90                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  91                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  92                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  93                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  94                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  95                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  96                     (cx.tcx.lang_items().partial_ord_trait(), true)
  97                 },
  98             };
  99             if let Some(trait_id) = trait_id {
 100                 #[allow(clippy::match_same_arms)]
 101                 match (&left.kind, &right.kind) {
 102                     // do not suggest to dereference literals
 103                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 104                     // &foo == &bar
 105                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 106                         let lty = cx.typeck_results().expr_ty(l);
 107                         let rty = cx.typeck_results().expr_ty(r);
 108                         let lcpy = is_copy(cx, lty);
 109                         let rcpy = is_copy(cx, rty);
 110                         // either operator autorefs or both args are copyable
 111                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 112                             span_lint_and_then(
 113                                 cx,
 114                                 OP_REF,
 115                                 e.span,
 116                                 "needlessly taken reference of both operands",
 117                                 |diag| {
 118                                     let lsnip = snippet(cx, l.span, "...").to_string();
 119                                     let rsnip = snippet(cx, r.span, "...").to_string();
 120                                     multispan_sugg(
 121                                         diag,
 122                                         "use the values directly",
 123                                         vec![(left.span, lsnip), (right.span, rsnip)],
 124                                     );
 125                                 },
 126                             )
 127                         } else if lcpy
 128                             && !rcpy
 129                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 130                         {
 131                             span_lint_and_then(
 132                                 cx,
 133                                 OP_REF,
 134                                 e.span,
 135                                 "needlessly taken reference of left operand",
 136                                 |diag| {
 137                                     let lsnip = snippet(cx, l.span, "...").to_string();
 138                                     diag.span_suggestion(
 139                                         left.span,
 140                                         "use the left value directly",
 141                                         lsnip,
 142                                         Applicability::MaybeIncorrect, // FIXME #2597
 143                                     );
 144                                 },
 145                             )
 146                         } else if !lcpy
 147                             && rcpy
 148                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 149                         {
 150                             span_lint_and_then(
 151                                 cx,
 152                                 OP_REF,
 153                                 e.span,
 154                                 "needlessly taken reference of right operand",
 155                                 |diag| {
 156                                     let rsnip = snippet(cx, r.span, "...").to_string();
 157                                     diag.span_suggestion(
 158                                         right.span,
 159                                         "use the right value directly",
 160                                         rsnip,
 161                                         Applicability::MaybeIncorrect, // FIXME #2597
 162                                     );
 163                                 },
 164                             )
 165                         }
 166                     },
 167                     // &foo == bar
 168                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), _) => {
 169                         let lty = cx.typeck_results().expr_ty(l);
 170                         let lcpy = is_copy(cx, lty);
 171                         if (requires_ref || lcpy)
 172                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 173                         {
 174                             span_lint_and_then(
 175                                 cx,
 176                                 OP_REF,
 177                                 e.span,
 178                                 "needlessly taken reference of left operand",
 179                                 |diag| {
 180                                     let lsnip = snippet(cx, l.span, "...").to_string();
 181                                     diag.span_suggestion(
 182                                         left.span,
 183                                         "use the left value directly",
 184                                         lsnip,
 185                                         Applicability::MaybeIncorrect, // FIXME #2597
 186                                     );
 187                                 },
 188                             )
 189                         }
 190                     },
 191                     // foo == &bar
 192                     (_, &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 193                         let rty = cx.typeck_results().expr_ty(r);
 194                         let rcpy = is_copy(cx, rty);
 195                         if (requires_ref || rcpy)
 196                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 197                         {
 198                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |diag| {
 199                                 let rsnip = snippet(cx, r.span, "...").to_string();
 200                                 diag.span_suggestion(
 201                                     right.span,
 202                                     "use the right value directly",
 203                                     rsnip,
 204                                     Applicability::MaybeIncorrect, // FIXME #2597
 205                                 );
 206                             })
 207                         }
 208                     },
 209                     _ => {},
 210                 }
 211             }
 212         }
 213     }
 214 }
 215
 216 fn is_valid_operator(op: BinOp) -> bool {
 217     matches!(
 218         op.node,
 219         BinOpKind::Sub
 220             | BinOpKind::Div
 221             | BinOpKind::Eq
 222             | BinOpKind::Lt
 223             | BinOpKind::Le
 224             | BinOpKind::Gt
 225             | BinOpKind::Ge
 226             | BinOpKind::Ne
 227             | BinOpKind::And
 228             | BinOpKind::Or
 229             | BinOpKind::BitXor
 230             | BinOpKind::BitAnd
 231             | BinOpKind::BitOr
 232     )
 233 }