1 use clippy_utils::{diagnostics::span_lint_and_help, path_def_id, ty::peel_mid_ty_refs};
2 use rustc_hir::{Expr, ExprKind};
3 use rustc_lint::{LateContext, LateLintPass};
4 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 /// Checks for calls to `std::mem::size_of_val()` where the argument is
11 /// a reference to a reference.
13 /// ### Why is this bad?
15 /// Calling `size_of_val()` with a reference to a reference as the argument
16 /// yields the size of the reference-type, not the size of the value behind
26 /// fn size(&self) -> usize {
27 /// // Note that `&self` as an argument is a `&&Foo`: Because `self`
28 /// // is already a reference, `&self` is a double-reference.
29 /// // The return value of `size_of_val()` therefor is the
30 /// // size of the reference-type, not the size of `self`.
31 /// std::mem::size_of_val(&self)
42 /// fn size(&self) -> usize {
44 /// std::mem::size_of_val(self)
48 #[clippy::version = "1.67.0"]
51 "Argument to `std::mem::size_of_val()` is a double-reference, which is almost certainly unintended"
53 declare_lint_pass!(SizeOfRef => [SIZE_OF_REF]);
55 impl LateLintPass<'_> for SizeOfRef {
56 fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
57 if let ExprKind::Call(path, [arg]) = expr.kind
58 && let Some(def_id) = path_def_id(cx, path)
59 && cx.tcx.is_diagnostic_item(sym::mem_size_of_val, def_id)
60 && let arg_ty = cx.typeck_results().expr_ty(arg)
61 && peel_mid_ty_refs(arg_ty).1 > 1
67 "argument to `std::mem::size_of_val()` is a reference to a reference",
69 "dereference the argument to `std::mem::size_of_val()` to get the size of the value instead of the size of the reference-type",