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