clippy_lints/src/unnamed_address.rs

   1 use crate::utils::{match_def_path, paths, span_lint, span_lint_and_help};
   2 use if_chain::if_chain;
   3 use rustc_hir::{BinOpKind, Expr, ExprKind};
   4 use rustc_lint::{LateContext, LateLintPass};
   5 use rustc_middle::ty;
   6 use rustc_session::{declare_lint_pass, declare_tool_lint};
   7
   8 declare_clippy_lint! {
   9     /// **What it does:** Checks for comparisons with an address of a function item.
  10     ///
  11     /// **Why is this bad?** Function item address is not guaranteed to be unique and could vary
  12     /// between different code generation units. Furthermore different function items could have
  13     /// the same address after being merged together.
  14     ///
  15     /// **Known problems:** None.
  16     ///
  17     /// **Example:**
  18     ///
  19     /// ```rust
  20     /// type F = fn();
  21     /// fn a() {}
  22     /// let f: F = a;
  23     /// if f == a {
  24     ///     // ...
  25     /// }
  26     /// ```
  27     pub FN_ADDRESS_COMPARISONS,
  28     correctness,
  29     "comparison with an address of a function item"
  30 }
  31
  32 declare_clippy_lint! {
  33     /// **What it does:** Checks for comparisons with an address of a trait vtable.
  34     ///
  35     /// **Why is this bad?** Comparing trait objects pointers compares an vtable addresses which
  36     /// are not guaranteed to be unique and could vary between different code generation units.
  37     /// Furthermore vtables for different types could have the same address after being merged
  38     /// together.
  39     ///
  40     /// **Known problems:** None.
  41     ///
  42     /// **Example:**
  43     ///
  44     /// ```rust,ignore
  45     /// let a: Rc<dyn Trait> = ...
  46     /// let b: Rc<dyn Trait> = ...
  47     /// if Rc::ptr_eq(&a, &b) {
  48     ///     ...
  49     /// }
  50     /// ```
  51     pub VTABLE_ADDRESS_COMPARISONS,
  52     correctness,
  53     "comparison with an address of a trait vtable"
  54 }
  55
  56 declare_lint_pass!(UnnamedAddress => [FN_ADDRESS_COMPARISONS, VTABLE_ADDRESS_COMPARISONS]);
  57
  58 impl LateLintPass<'_, '_> for UnnamedAddress {
  59     fn check_expr(&mut self, cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
  60         fn is_comparison(binop: BinOpKind) -> bool {
  61             match binop {
  62                 BinOpKind::Eq | BinOpKind::Lt | BinOpKind::Le | BinOpKind::Ne | BinOpKind::Ge | BinOpKind::Gt => true,
  63                 _ => false,
  64             }
  65         }
  66
  67         fn is_trait_ptr(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
  68             match cx.tables.expr_ty_adjusted(expr).kind {
  69                 ty::RawPtr(ty::TypeAndMut { ty, .. }) => ty.is_trait(),
  70                 _ => false,
  71             }
  72         }
  73
  74         fn is_fn_def(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool {
  75             if let ty::FnDef(..) = cx.tables.expr_ty(expr).kind {
  76                 true
  77             } else {
  78                 false
  79             }
  80         }
  81
  82         if_chain! {
  83             if let ExprKind::Binary(binop, ref left, ref right) = expr.kind;
  84             if is_comparison(binop.node);
  85             if is_trait_ptr(cx, left) && is_trait_ptr(cx, right);
  86             then {
  87                 span_lint_and_help(
  88                     cx,
  89                     VTABLE_ADDRESS_COMPARISONS,
  90                     expr.span,
  91                     "comparing trait object pointers compares a non-unique vtable address",
  92                     "consider extracting and comparing data pointers only",
  93                 );
  94             }
  95         }
  96
  97         if_chain! {
  98             if let ExprKind::Call(ref func, [ref _left, ref _right]) = expr.kind;
  99             if let ExprKind::Path(ref func_qpath) = func.kind;
 100             if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id();
 101             if match_def_path(cx, def_id, &paths::PTR_EQ) ||
 102                 match_def_path(cx, def_id, &paths::RC_PTR_EQ) ||
 103                 match_def_path(cx, def_id, &paths::ARC_PTR_EQ);
 104             let ty_param = cx.tables.node_substs(func.hir_id).type_at(0);
 105             if ty_param.is_trait();
 106             then {
 107                 span_lint_and_help(
 108                     cx,
 109                     VTABLE_ADDRESS_COMPARISONS,
 110                     expr.span,
 111                     "comparing trait object pointers compares a non-unique vtable address",
 112                     "consider extracting and comparing data pointers only",
 113                 );
 114             }
 115         }
 116
 117         if_chain! {
 118             if let ExprKind::Binary(binop, ref left, ref right) = expr.kind;
 119             if is_comparison(binop.node);
 120             if cx.tables.expr_ty_adjusted(left).is_fn_ptr() &&
 121                 cx.tables.expr_ty_adjusted(right).is_fn_ptr();
 122             if is_fn_def(cx, left) || is_fn_def(cx, right);
 123             then {
 124                 span_lint(
 125                     cx,
 126                     FN_ADDRESS_COMPARISONS,
 127                     expr.span,
 128                     "comparing with a non-unique address of a function item",
 129                 );
 130             }
 131         }
 132     }
 133 }