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