clippy_lints/src/eq_op.rs

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