clippy_lints/src/eq_op.rs

   1 use crate::utils::{
   2     ast_utils::is_useless_with_eq_exprs, eq_expr_value, higher, in_macro, is_expn_of, multispan_sugg, span_lint,
   3     span_lint_and_then,
   4 };
   5 use clippy_utils::source::snippet;
   6 use clippy_utils::ty::{implements_trait, is_copy};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::{BinOpKind, BorrowKind, Expr, ExprKind, StmtKind};
  10 use rustc_lint::{LateContext, LateLintPass};
  11 use rustc_session::{declare_lint_pass, declare_tool_lint};
  12
  13 declare_clippy_lint! {
  14     /// **What it does:** Checks for equal operands to comparison, logical and
  15     /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  16     /// `||`, `&`, `|`, `^`, `-` and `/`).
  17     ///
  18     /// **Why is this bad?** This is usually just a typo or a copy and paste error.
  19     ///
  20     /// **Known problems:** False negatives: We had some false positives regarding
  21     /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  22     /// of `x.pop() && x.pop()`), so we removed matching any function or method
  23     /// calls. We may introduce a list of known pure functions in the future.
  24     ///
  25     /// **Example:**
  26     /// ```rust
  27     /// # let x = 1;
  28     /// if x + 1 == x + 1 {}
  29     /// ```
  30     /// or
  31     /// ```rust
  32     /// # let a = 3;
  33     /// # let b = 4;
  34     /// assert_eq!(a, a);
  35     /// ```
  36     pub EQ_OP,
  37     correctness,
  38     "equal operands on both sides of a comparison or bitwise combination (e.g., `x == x`)"
  39 }
  40
  41 declare_clippy_lint! {
  42     /// **What it does:** Checks for arguments to `==` which have their address
  43     /// taken to satisfy a bound
  44     /// and suggests to dereference the other argument instead
  45     ///
  46     /// **Why is this bad?** It is more idiomatic to dereference the other argument.
  47     ///
  48     /// **Known problems:** None
  49     ///
  50     /// **Example:**
  51     /// ```ignore
  52     /// // Bad
  53     /// &x == y
  54     ///
  55     /// // Good
  56     /// x == *y
  57     /// ```
  58     pub OP_REF,
  59     style,
  60     "taking a reference to satisfy the type constraints on `==`"
  61 }
  62
  63 declare_lint_pass!(EqOp => [EQ_OP, OP_REF]);
  64
  65 const ASSERT_MACRO_NAMES: [&str; 4] = ["assert_eq", "assert_ne", "debug_assert_eq", "debug_assert_ne"];
  66
  67 impl<'tcx> LateLintPass<'tcx> for EqOp {
  68     #[allow(clippy::similar_names, clippy::too_many_lines)]
  69     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  70         if let ExprKind::Block(ref block, _) = e.kind {
  71             for stmt in block.stmts {
  72                 for amn in &ASSERT_MACRO_NAMES {
  73                     if_chain! {
  74                         if is_expn_of(stmt.span, amn).is_some();
  75                         if let StmtKind::Semi(ref matchexpr) = stmt.kind;
  76                         if let Some(macro_args) = higher::extract_assert_macro_args(matchexpr);
  77                         if macro_args.len() == 2;
  78                         let (lhs, rhs) = (macro_args[0], macro_args[1]);
  79                         if eq_expr_value(cx, lhs, rhs);
  80
  81                         then {
  82                             span_lint(
  83                                 cx,
  84                                 EQ_OP,
  85                                 lhs.span.to(rhs.span),
  86                                 &format!("identical args used in this `{}!` macro call", amn),
  87                             );
  88                         }
  89                     }
  90                 }
  91             }
  92         }
  93         if let ExprKind::Binary(op, ref left, ref right) = e.kind {
  94             if e.span.from_expansion() {
  95                 return;
  96             }
  97             let macro_with_not_op = |expr_kind: &ExprKind<'_>| {
  98                 if let ExprKind::Unary(_, ref expr) = *expr_kind {
  99                     in_macro(expr.span)
 100                 } else {
 101                     false
 102                 }
 103             };
 104             if macro_with_not_op(&left.kind) || macro_with_not_op(&right.kind) {
 105                 return;
 106             }
 107             if is_useless_with_eq_exprs(higher::binop(op.node)) && eq_expr_value(cx, left, right) {
 108                 span_lint(
 109                     cx,
 110                     EQ_OP,
 111                     e.span,
 112                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
 113                 );
 114                 return;
 115             }
 116             let (trait_id, requires_ref) = match op.node {
 117                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
 118                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
 119                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
 120                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
 121                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
 122                 // don't lint short circuiting ops
 123                 BinOpKind::And | BinOpKind::Or => return,
 124                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
 125                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
 126                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
 127                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
 128                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
 129                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
 130                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
 131                     (cx.tcx.lang_items().partial_ord_trait(), true)
 132                 },
 133             };
 134             if let Some(trait_id) = trait_id {
 135                 #[allow(clippy::match_same_arms)]
 136                 match (&left.kind, &right.kind) {
 137                     // do not suggest to dereference literals
 138                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 139                     // &foo == &bar
 140                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 141                         let lty = cx.typeck_results().expr_ty(l);
 142                         let rty = cx.typeck_results().expr_ty(r);
 143                         let lcpy = is_copy(cx, lty);
 144                         let rcpy = is_copy(cx, rty);
 145                         // either operator autorefs or both args are copyable
 146                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 147                             span_lint_and_then(
 148                                 cx,
 149                                 OP_REF,
 150                                 e.span,
 151                                 "needlessly taken reference of both operands",
 152                                 |diag| {
 153                                     let lsnip = snippet(cx, l.span, "...").to_string();
 154                                     let rsnip = snippet(cx, r.span, "...").to_string();
 155                                     multispan_sugg(
 156                                         diag,
 157                                         "use the values directly",
 158                                         vec![(left.span, lsnip), (right.span, rsnip)],
 159                                     );
 160                                 },
 161                             )
 162                         } else if lcpy
 163                             && !rcpy
 164                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 165                         {
 166                             span_lint_and_then(
 167                                 cx,
 168                                 OP_REF,
 169                                 e.span,
 170                                 "needlessly taken reference of left operand",
 171                                 |diag| {
 172                                     let lsnip = snippet(cx, l.span, "...").to_string();
 173                                     diag.span_suggestion(
 174                                         left.span,
 175                                         "use the left value directly",
 176                                         lsnip,
 177                                         Applicability::MaybeIncorrect, // FIXME #2597
 178                                     );
 179                                 },
 180                             )
 181                         } else if !lcpy
 182                             && rcpy
 183                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 184                         {
 185                             span_lint_and_then(
 186                                 cx,
 187                                 OP_REF,
 188                                 e.span,
 189                                 "needlessly taken reference of right operand",
 190                                 |diag| {
 191                                     let rsnip = snippet(cx, r.span, "...").to_string();
 192                                     diag.span_suggestion(
 193                                         right.span,
 194                                         "use the right value directly",
 195                                         rsnip,
 196                                         Applicability::MaybeIncorrect, // FIXME #2597
 197                                     );
 198                                 },
 199                             )
 200                         }
 201                     },
 202                     // &foo == bar
 203                     (&ExprKind::AddrOf(BorrowKind::Ref, _, ref l), _) => {
 204                         let lty = cx.typeck_results().expr_ty(l);
 205                         let lcpy = is_copy(cx, lty);
 206                         if (requires_ref || lcpy)
 207                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 208                         {
 209                             span_lint_and_then(
 210                                 cx,
 211                                 OP_REF,
 212                                 e.span,
 213                                 "needlessly taken reference of left operand",
 214                                 |diag| {
 215                                     let lsnip = snippet(cx, l.span, "...").to_string();
 216                                     diag.span_suggestion(
 217                                         left.span,
 218                                         "use the left value directly",
 219                                         lsnip,
 220                                         Applicability::MaybeIncorrect, // FIXME #2597
 221                                     );
 222                                 },
 223                             )
 224                         }
 225                     },
 226                     // foo == &bar
 227                     (_, &ExprKind::AddrOf(BorrowKind::Ref, _, ref r)) => {
 228                         let rty = cx.typeck_results().expr_ty(r);
 229                         let rcpy = is_copy(cx, rty);
 230                         if (requires_ref || rcpy)
 231                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 232                         {
 233                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |diag| {
 234                                 let rsnip = snippet(cx, r.span, "...").to_string();
 235                                 diag.span_suggestion(
 236                                     right.span,
 237                                     "use the right value directly",
 238                                     rsnip,
 239                                     Applicability::MaybeIncorrect, // FIXME #2597
 240                                 );
 241                             })
 242                         }
 243                     },
 244                     _ => {},
 245                 }
 246             }
 247         }
 248     }
 249 }