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