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 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 #[derive(Copy, Clone)]
  50 pub struct EqOp;
  51
  52 impl LintPass for EqOp {
  53     fn get_lints(&self) -> LintArray {
  54         lint_array!(EQ_OP, OP_REF)
  55     }
  56
  57     fn name(&self) -> &'static str {
  58         "EqOp"
  59     }
  60 }
  61
  62 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for EqOp {
  63     #[allow(clippy::similar_names, clippy::too_many_lines)]
  64     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
  65         if let ExprKind::Binary(op, ref left, ref right) = e.node {
  66             if in_macro(e.span) {
  67                 return;
  68             }
  69             if is_valid_operator(op) && SpanlessEq::new(cx).ignore_fn().eq_expr(left, right) {
  70                 span_lint(
  71                     cx,
  72                     EQ_OP,
  73                     e.span,
  74                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
  75                 );
  76                 return;
  77             }
  78             let (trait_id, requires_ref) = match op.node {
  79                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
  80                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
  81                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
  82                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
  83                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
  84                 // don't lint short circuiting ops
  85                 BinOpKind::And | BinOpKind::Or => return,
  86                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
  87                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
  88                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
  89                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
  90                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
  91                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
  92                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
  93                     (cx.tcx.lang_items().ord_trait(), true)
  94                 },
  95             };
  96             if let Some(trait_id) = trait_id {
  97                 #[allow(clippy::match_same_arms)]
  98                 match (&left.node, &right.node) {
  99                     // do not suggest to dereference literals
 100                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 101                     // &foo == &bar
 102                     (&ExprKind::AddrOf(_, ref l), &ExprKind::AddrOf(_, ref r)) => {
 103                         let lty = cx.tables.expr_ty(l);
 104                         let rty = cx.tables.expr_ty(r);
 105                         let lcpy = is_copy(cx, lty);
 106                         let rcpy = is_copy(cx, rty);
 107                         // either operator autorefs or both args are copyable
 108                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 109                             span_lint_and_then(
 110                                 cx,
 111                                 OP_REF,
 112                                 e.span,
 113                                 "needlessly taken reference of both operands",
 114                                 |db| {
 115                                     let lsnip = snippet(cx, l.span, "...").to_string();
 116                                     let rsnip = snippet(cx, r.span, "...").to_string();
 117                                     multispan_sugg(
 118                                         db,
 119                                         "use the values directly".to_string(),
 120                                         vec![(left.span, lsnip), (right.span, rsnip)],
 121                                     );
 122                                 },
 123                             )
 124                         } else if lcpy
 125                             && !rcpy
 126                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 127                         {
 128                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 129                                 let lsnip = snippet(cx, l.span, "...").to_string();
 130                                 db.span_suggestion(
 131                                     left.span,
 132                                     "use the left value directly",
 133                                     lsnip,
 134                                     Applicability::MachineApplicable, // snippet
 135                                 );
 136                             })
 137                         } else if !lcpy
 138                             && rcpy
 139                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 140                         {
 141                             span_lint_and_then(
 142                                 cx,
 143                                 OP_REF,
 144                                 e.span,
 145                                 "needlessly taken reference of right operand",
 146                                 |db| {
 147                                     let rsnip = snippet(cx, r.span, "...").to_string();
 148                                     db.span_suggestion(
 149                                         right.span,
 150                                         "use the right value directly",
 151                                         rsnip,
 152                                         Applicability::MachineApplicable, // snippet
 153                                     );
 154                                 },
 155                             )
 156                         }
 157                     },
 158                     // &foo == bar
 159                     (&ExprKind::AddrOf(_, ref l), _) => {
 160                         let lty = cx.tables.expr_ty(l);
 161                         let lcpy = is_copy(cx, lty);
 162                         if (requires_ref || lcpy)
 163                             && implements_trait(cx, lty, trait_id, &[cx.tables.expr_ty(right).into()])
 164                         {
 165                             span_lint_and_then(cx, OP_REF, e.span, "needlessly taken reference of left operand", |db| {
 166                                 let lsnip = snippet(cx, l.span, "...").to_string();
 167                                 db.span_suggestion(
 168                                     left.span,
 169                                     "use the left value directly",
 170                                     lsnip,
 171                                     Applicability::MachineApplicable, // snippet
 172                                 );
 173                             })
 174                         }
 175                     },
 176                     // foo == &bar
 177                     (_, &ExprKind::AddrOf(_, ref r)) => {
 178                         let rty = cx.tables.expr_ty(r);
 179                         let rcpy = is_copy(cx, rty);
 180                         if (requires_ref || rcpy)
 181                             && implements_trait(cx, cx.tables.expr_ty(left), trait_id, &[rty.into()])
 182                         {
 183                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |db| {
 184                                 let rsnip = snippet(cx, r.span, "...").to_string();
 185                                 db.span_suggestion(
 186                                     right.span,
 187                                     "use the right value directly",
 188                                     rsnip,
 189                                     Applicability::MachineApplicable, // snippet
 190                                 );
 191                             })
 192                         }
 193                     },
 194                     _ => {},
 195                 }
 196             }
 197         }
 198     }
 199 }
 200
 201 fn is_valid_operator(op: BinOp) -> bool {
 202     match op.node {
 203         BinOpKind::Sub
 204         | BinOpKind::Div
 205         | BinOpKind::Eq
 206         | BinOpKind::Lt
 207         | BinOpKind::Le
 208         | BinOpKind::Gt
 209         | BinOpKind::Ge
 210         | BinOpKind::Ne
 211         | BinOpKind::And
 212         | BinOpKind::Or
 213         | BinOpKind::BitXor
 214         | BinOpKind::BitAnd
 215         | BinOpKind::BitOr => true,
 216         _ => false,
 217     }
 218 }