clippy_lints/src/eq_op.rs

   1 use clippy_utils::diagnostics::{multispan_sugg, span_lint, span_lint_and_then};
   2 use clippy_utils::get_enclosing_block;
   3 use clippy_utils::macros::{find_assert_eq_args, first_node_macro_backtrace};
   4 use clippy_utils::source::snippet;
   5 use clippy_utils::ty::{implements_trait, is_copy};
   6 use clippy_utils::{ast_utils::is_useless_with_eq_exprs, eq_expr_value, is_in_test_function};
   7 use if_chain::if_chain;
   8 use rustc_errors::Applicability;
   9 use rustc_hir::{
  10     def::Res, def_id::DefId, BinOpKind, BorrowKind, Expr, ExprKind, GenericArg, ItemKind, QPath, Ty, TyKind,
  11 };
  12 use rustc_lint::{LateContext, LateLintPass};
  13 use rustc_middle::ty::{self, TyS};
  14 use rustc_session::{declare_lint_pass, declare_tool_lint};
  15
  16 declare_clippy_lint! {
  17     /// ### What it does
  18     /// Checks for equal operands to comparison, logical and
  19     /// bitwise, difference and division binary operators (`==`, `>`, etc., `&&`,
  20     /// `||`, `&`, `|`, `^`, `-` and `/`).
  21     ///
  22     /// ### Why is this bad?
  23     /// This is usually just a typo or a copy and paste error.
  24     ///
  25     /// ### Known problems
  26     /// False negatives: We had some false positives regarding
  27     /// calls (notably [racer](https://github.com/phildawes/racer) had one instance
  28     /// of `x.pop() && x.pop()`), so we removed matching any function or method
  29     /// calls. We may introduce a list of known pure functions in the future.
  30     ///
  31     /// ### Example
  32     /// ```rust
  33     /// # let x = 1;
  34     /// if x + 1 == x + 1 {}
  35     /// ```
  36     /// or
  37     /// ```rust
  38     /// # let a = 3;
  39     /// # let b = 4;
  40     /// assert_eq!(a, a);
  41     /// ```
  42     #[clippy::version = "pre 1.29.0"]
  43     pub EQ_OP,
  44     correctness,
  45     "equal operands on both sides of a comparison or bitwise combination (e.g., `x == x`)"
  46 }
  47
  48 declare_clippy_lint! {
  49     /// ### What it does
  50     /// Checks for arguments to `==` which have their address
  51     /// taken to satisfy a bound
  52     /// and suggests to dereference the other argument instead
  53     ///
  54     /// ### Why is this bad?
  55     /// It is more idiomatic to dereference the other argument.
  56     ///
  57     /// ### Known problems
  58     /// None
  59     ///
  60     /// ### Example
  61     /// ```ignore
  62     /// // Bad
  63     /// &x == y
  64     ///
  65     /// // Good
  66     /// x == *y
  67     /// ```
  68     #[clippy::version = "pre 1.29.0"]
  69     pub OP_REF,
  70     style,
  71     "taking a reference to satisfy the type constraints on `==`"
  72 }
  73
  74 declare_lint_pass!(EqOp => [EQ_OP, OP_REF]);
  75
  76 impl<'tcx> LateLintPass<'tcx> for EqOp {
  77     #[allow(clippy::similar_names, clippy::too_many_lines)]
  78     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
  79         if_chain! {
  80             if let Some((macro_call, macro_name)) = first_node_macro_backtrace(cx, e).find_map(|macro_call| {
  81                 let name = cx.tcx.item_name(macro_call.def_id);
  82                 matches!(name.as_str(), "assert_eq" | "assert_ne" | "debug_assert_eq" | "debug_assert_ne")
  83                     .then(|| (macro_call, name))
  84             });
  85             if let Some((lhs, rhs, _)) = find_assert_eq_args(cx, e, macro_call.expn);
  86             if eq_expr_value(cx, lhs, rhs);
  87             if macro_call.is_local();
  88             if !is_in_test_function(cx.tcx, e.hir_id);
  89             then {
  90                 span_lint(
  91                     cx,
  92                     EQ_OP,
  93                     lhs.span.to(rhs.span),
  94                     &format!("identical args used in this `{}!` macro call", macro_name),
  95                 );
  96             }
  97         }
  98         if let ExprKind::Binary(op, left, right) = e.kind {
  99             if e.span.from_expansion() {
 100                 return;
 101             }
 102             let macro_with_not_op = |expr_kind: &ExprKind<'_>| {
 103                 if let ExprKind::Unary(_, expr) = *expr_kind {
 104                     expr.span.from_expansion()
 105                 } else {
 106                     false
 107                 }
 108             };
 109             if macro_with_not_op(&left.kind) || macro_with_not_op(&right.kind) {
 110                 return;
 111             }
 112             if is_useless_with_eq_exprs(op.node.into())
 113                 && eq_expr_value(cx, left, right)
 114                 && !is_in_test_function(cx.tcx, e.hir_id)
 115             {
 116                 span_lint(
 117                     cx,
 118                     EQ_OP,
 119                     e.span,
 120                     &format!("equal expressions as operands to `{}`", op.node.as_str()),
 121                 );
 122                 return;
 123             }
 124             let (trait_id, requires_ref) = match op.node {
 125                 BinOpKind::Add => (cx.tcx.lang_items().add_trait(), false),
 126                 BinOpKind::Sub => (cx.tcx.lang_items().sub_trait(), false),
 127                 BinOpKind::Mul => (cx.tcx.lang_items().mul_trait(), false),
 128                 BinOpKind::Div => (cx.tcx.lang_items().div_trait(), false),
 129                 BinOpKind::Rem => (cx.tcx.lang_items().rem_trait(), false),
 130                 // don't lint short circuiting ops
 131                 BinOpKind::And | BinOpKind::Or => return,
 132                 BinOpKind::BitXor => (cx.tcx.lang_items().bitxor_trait(), false),
 133                 BinOpKind::BitAnd => (cx.tcx.lang_items().bitand_trait(), false),
 134                 BinOpKind::BitOr => (cx.tcx.lang_items().bitor_trait(), false),
 135                 BinOpKind::Shl => (cx.tcx.lang_items().shl_trait(), false),
 136                 BinOpKind::Shr => (cx.tcx.lang_items().shr_trait(), false),
 137                 BinOpKind::Ne | BinOpKind::Eq => (cx.tcx.lang_items().eq_trait(), true),
 138                 BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ge | BinOpKind::Gt => {
 139                     (cx.tcx.lang_items().partial_ord_trait(), true)
 140                 },
 141             };
 142             if let Some(trait_id) = trait_id {
 143                 #[allow(clippy::match_same_arms)]
 144                 match (&left.kind, &right.kind) {
 145                     // do not suggest to dereference literals
 146                     (&ExprKind::Lit(..), _) | (_, &ExprKind::Lit(..)) => {},
 147                     // &foo == &bar
 148                     (&ExprKind::AddrOf(BorrowKind::Ref, _, l), &ExprKind::AddrOf(BorrowKind::Ref, _, r)) => {
 149                         let lty = cx.typeck_results().expr_ty(l);
 150                         let rty = cx.typeck_results().expr_ty(r);
 151                         let lcpy = is_copy(cx, lty);
 152                         let rcpy = is_copy(cx, rty);
 153                         if let Some((self_ty, other_ty)) = in_impl(cx, e, trait_id) {
 154                             if (are_equal(cx, rty, self_ty) && are_equal(cx, lty, other_ty))
 155                                 || (are_equal(cx, rty, other_ty) && are_equal(cx, lty, self_ty))
 156                             {
 157                                 return; // Don't lint
 158                             }
 159                         }
 160                         // either operator autorefs or both args are copyable
 161                         if (requires_ref || (lcpy && rcpy)) && implements_trait(cx, lty, trait_id, &[rty.into()]) {
 162                             span_lint_and_then(
 163                                 cx,
 164                                 OP_REF,
 165                                 e.span,
 166                                 "needlessly taken reference of both operands",
 167                                 |diag| {
 168                                     let lsnip = snippet(cx, l.span, "...").to_string();
 169                                     let rsnip = snippet(cx, r.span, "...").to_string();
 170                                     multispan_sugg(
 171                                         diag,
 172                                         "use the values directly",
 173                                         vec![(left.span, lsnip), (right.span, rsnip)],
 174                                     );
 175                                 },
 176                             );
 177                         } else if lcpy
 178                             && !rcpy
 179                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 180                         {
 181                             span_lint_and_then(
 182                                 cx,
 183                                 OP_REF,
 184                                 e.span,
 185                                 "needlessly taken reference of left operand",
 186                                 |diag| {
 187                                     let lsnip = snippet(cx, l.span, "...").to_string();
 188                                     diag.span_suggestion(
 189                                         left.span,
 190                                         "use the left value directly",
 191                                         lsnip,
 192                                         Applicability::MaybeIncorrect, // FIXME #2597
 193                                     );
 194                                 },
 195                             );
 196                         } else if !lcpy
 197                             && rcpy
 198                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 199                         {
 200                             span_lint_and_then(
 201                                 cx,
 202                                 OP_REF,
 203                                 e.span,
 204                                 "needlessly taken reference of right operand",
 205                                 |diag| {
 206                                     let rsnip = snippet(cx, r.span, "...").to_string();
 207                                     diag.span_suggestion(
 208                                         right.span,
 209                                         "use the right value directly",
 210                                         rsnip,
 211                                         Applicability::MaybeIncorrect, // FIXME #2597
 212                                     );
 213                                 },
 214                             );
 215                         }
 216                     },
 217                     // &foo == bar
 218                     (&ExprKind::AddrOf(BorrowKind::Ref, _, l), _) => {
 219                         let lty = cx.typeck_results().expr_ty(l);
 220                         if let Some((self_ty, other_ty)) = in_impl(cx, e, trait_id) {
 221                             let rty = cx.typeck_results().expr_ty(right);
 222                             if (are_equal(cx, rty, self_ty) && are_equal(cx, lty, other_ty))
 223                                 || (are_equal(cx, rty, other_ty) && are_equal(cx, lty, self_ty))
 224                             {
 225                                 return; // Don't lint
 226                             }
 227                         }
 228                         let lcpy = is_copy(cx, lty);
 229                         if (requires_ref || lcpy)
 230                             && implements_trait(cx, lty, trait_id, &[cx.typeck_results().expr_ty(right).into()])
 231                         {
 232                             span_lint_and_then(
 233                                 cx,
 234                                 OP_REF,
 235                                 e.span,
 236                                 "needlessly taken reference of left operand",
 237                                 |diag| {
 238                                     let lsnip = snippet(cx, l.span, "...").to_string();
 239                                     diag.span_suggestion(
 240                                         left.span,
 241                                         "use the left value directly",
 242                                         lsnip,
 243                                         Applicability::MaybeIncorrect, // FIXME #2597
 244                                     );
 245                                 },
 246                             );
 247                         }
 248                     },
 249                     // foo == &bar
 250                     (_, &ExprKind::AddrOf(BorrowKind::Ref, _, r)) => {
 251                         let rty = cx.typeck_results().expr_ty(r);
 252                         if let Some((self_ty, other_ty)) = in_impl(cx, e, trait_id) {
 253                             let lty = cx.typeck_results().expr_ty(left);
 254                             if (are_equal(cx, rty, self_ty) && are_equal(cx, lty, other_ty))
 255                                 || (are_equal(cx, rty, other_ty) && are_equal(cx, lty, self_ty))
 256                             {
 257                                 return; // Don't lint
 258                             }
 259                         }
 260                         let rcpy = is_copy(cx, rty);
 261                         if (requires_ref || rcpy)
 262                             && implements_trait(cx, cx.typeck_results().expr_ty(left), trait_id, &[rty.into()])
 263                         {
 264                             span_lint_and_then(cx, OP_REF, e.span, "taken reference of right operand", |diag| {
 265                                 let rsnip = snippet(cx, r.span, "...").to_string();
 266                                 diag.span_suggestion(
 267                                     right.span,
 268                                     "use the right value directly",
 269                                     rsnip,
 270                                     Applicability::MaybeIncorrect, // FIXME #2597
 271                                 );
 272                             });
 273                         }
 274                     },
 275                     _ => {},
 276                 }
 277             }
 278         }
 279     }
 280 }
 281
 282 fn in_impl<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, bin_op: DefId) -> Option<(&'tcx Ty<'tcx>, &'tcx Ty<'tcx>)> {
 283     if_chain! {
 284         if let Some(block) = get_enclosing_block(cx, e.hir_id);
 285         if let Some(impl_def_id) = cx.tcx.impl_of_method(block.hir_id.owner.to_def_id());
 286         let item = cx.tcx.hir().expect_item(impl_def_id.expect_local());
 287         if let ItemKind::Impl(item) = &item.kind;
 288         if let Some(of_trait) = &item.of_trait;
 289         if let Some(seg) = of_trait.path.segments.last();
 290         if let Some(Res::Def(_, trait_id)) = seg.res;
 291         if trait_id == bin_op;
 292         if let Some(generic_args) = seg.args;
 293         if let Some(GenericArg::Type(other_ty)) = generic_args.args.last();
 294
 295         then {
 296             Some((item.self_ty, other_ty))
 297         }
 298         else {
 299             None
 300         }
 301     }
 302 }
 303
 304 fn are_equal<'tcx>(cx: &LateContext<'tcx>, middle_ty: &TyS<'_>, hir_ty: &Ty<'_>) -> bool {
 305     if_chain! {
 306         if let ty::Adt(adt_def, _) = middle_ty.kind();
 307         if let Some(local_did) = adt_def.did.as_local();
 308         let item = cx.tcx.hir().expect_item(local_did);
 309         let middle_ty_id = item.def_id.to_def_id();
 310         if let TyKind::Path(QPath::Resolved(_, path)) = hir_ty.kind;
 311         if let Res::Def(_, hir_ty_id) = path.res;
 312
 313         then {
 314             hir_ty_id == middle_ty_id
 315         }
 316         else {
 317             false
 318         }
 319     }
 320 }