clippy_lints/src/eq_op.rs

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