clippy_lints/src/eq_op.rs

   1 use crate::utils::{
   2     implements_trait, in_macro_or_desugar, is_copy, multispan_sugg, snippet, span_lint, span_lint_and_then, SpanlessEq,
   3 };
   4 use rustc::hir::*;
   5 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
   6 use rustc::{declare_lint_pass, declare_tool_lint};
   7 use rustc_errors::Applicability;
   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.node {
  55             if in_macro_or_desugar(e.span) {
  56                 return;
  57             }
  58             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  59                 span_lint(
  60                     cx,
  61                     EQ_OP,
  62                     e.span,
  63                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  64                 );
  65                 return;
  66             }
  67             let (trait_id, requires_ref) = match op.node {
  68                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  69                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  70                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  71                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  72                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  73                 // don't lint short circuiting ops
  74                 BinOpKind::And | BinOpKind::Or => return,
  75                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  76                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  77                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  78                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  79                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  80                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  81                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  82                     (cx.tcx.lang_items().ord_trait(), true)
  83                 },
  84             };
  85             if let Some(trait_id) = trait_id {
  86                 #[allow(clippy::match_same_arms)]
  87                 match (&left.node, &right.node) {
  88                     // do not suggest to dereference literals
  89                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
  90                     // &foo == &bar
  91                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
  92                         let lty = cx.tables.expr_ty(l);
  93                         let rty = cx.tables.expr_ty(r);
  94                         let lcpy = is_copy(cx, lty);
  95                         let rcpy = is_copy(cx, rty);
  96                         // either operator autorefs or both args are copyable
  97                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
  98                             span_lint_and_then(
  99                                 cx,
 100                                 OP_REF,
 101                                 e.span,
 102                                 "needlessly taken reference of both operands",
 103                                 |db| {
 104                                     let lsnip = snippet(cx, l.span, "...").to_string();
 105                                     let rsnip = snippet(cx, r.span, "...").to_string();
 106                                     multispan_sugg(
 107                                         db,
 108                                         "use the values directly".to_string(),
 109                                         vec![(left.span, lsnip), (right.span, rsnip)],
 110                                     );
 111                                 },
 112                             )
 113                         } else if lcpy
 114                             && !rcpy
 115                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 116                         {
 117                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 118                                 let lsnip = snippet(cx, l.span, "...").to_string();
 119                                 db.span_suggestion(
 120                                     left.span,
 121                                     "use the left value directly",
 122                                     lsnip,
 123                                     Applicability::MachineApplicable, // snippet
 124                                 );
 125                             })
 126                         } else if !lcpy
 127                             && rcpy
 128                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 129                         {
 130                             span_lint_and_then(
 131                                 cx,
 132                                 OP_REF,
 133                                 e.span,
 134                                 "needlessly taken reference of right operand",
 135                                 |db| {
 136                                     let rsnip = snippet(cx, r.span, "...").to_string();
 137                                     db.span_suggestion(
 138                                         right.span,
 139                                         "use the right value directly",
 140                                         rsnip,
 141                                         Applicability::MachineApplicable, // snippet
 142                                     );
 143                                 },
 144                             )
 145                         }
 146                     },
 147                     // &foo == bar
 148                     (&ExprKind::AddrOf(_, ref l), _) => {
 149                         let lty = cx.tables.expr_ty(l);
 150                         let lcpy = is_copy(cx, lty);
 151                         if (requires_ref || lcpy)
 152                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 153                         {
 154                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 155                                 let lsnip = snippet(cx, l.span, "...").to_string();
 156                                 db.span_suggestion(
 157                                     left.span,
 158                                     "use the left value directly",
 159                                     lsnip,
 160                                     Applicability::MachineApplicable, // snippet
 161                                 );
 162                             })
 163                         }
 164                     },
 165                     // foo == &bar
 166                     (_, &ExprKind::AddrOf(_, ref r)) => {
 167                         let rty = cx.tables.expr_ty(r);
 168                         let rcpy = is_copy(cx, rty);
 169                         if (requires_ref || rcpy)
 170                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 171                         {
 172                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 173                                 let rsnip = snippet(cx, r.span, "...").to_string();
 174                                 db.span_suggestion(
 175                                     right.span,
 176                                     "use the right value directly",
 177                                     rsnip,
 178                                     Applicability::MachineApplicable, // snippet
 179                                 );
 180                             })
 181                         }
 182                     },
 183                     _ => {},
 184                 }
 185             }
 186         }
 187     }
 188 }
 189
 190 fn is_valid_operator(op: BinOp) -> bool {
 191     match op.node {
 192         BinOpKind::Sub
 193         | BinOpKind::Div
 194         | BinOpKind::Eq
 195         | BinOpKind::Lt
 196         | BinOpKind::Le
 197         | BinOpKind::Gt
 198         | BinOpKind::Ge
 199         | BinOpKind::Ne
 200         | BinOpKind::And
 201         | BinOpKind::Or
 202         | BinOpKind::BitXor
 203         | BinOpKind::BitAnd
 204         | BinOpKind::BitOr => true,
 205         _ => false,
 206     }
 207 }