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