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use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::path_def_id;
use clippy_utils::ty::peel_mid_ty_refs;
use rustc_hir::{Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
///
/// Checks for calls to `std::mem::size_of_val()` where the argument is
/// a reference to a reference.
///
/// ### Why is this bad?
///
/// Calling `size_of_val()` with a reference to a reference as the argument
/// yields the size of the reference-type, not the size of the value behind
/// the reference.
///
/// ### Example
/// ```rust
/// struct Foo {
/// buffer: [u8],
/// }
///
/// impl Foo {
/// fn size(&self) -> usize {
/// // Note that `&self` as an argument is a `&&Foo`: Because `self`
/// // is already a reference, `&self` is a double-reference.
/// // The return value of `size_of_val()` therefor is the
/// // size of the reference-type, not the size of `self`.
/// std::mem::size_of_val(&self)
/// }
/// }
/// ```
/// Use instead:
/// ```rust
/// struct Foo {
/// buffer: [u8],
/// }
///
/// impl Foo {
/// fn size(&self) -> usize {
/// // Correct
/// std::mem::size_of_val(self)
/// }
/// }
/// ```
#[clippy::version = "1.68.0"]
pub SIZE_OF_REF,
suspicious,
"Argument to `std::mem::size_of_val()` is a double-reference, which is almost certainly unintended"
}
declare_lint_pass!(SizeOfRef => [SIZE_OF_REF]);
impl LateLintPass<'_> for SizeOfRef {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
if let ExprKind::Call(path, [arg]) = expr.kind
&& let Some(def_id) = path_def_id(cx, path)
&& cx.tcx.is_diagnostic_item(sym::mem_size_of_val, def_id)
&& let arg_ty = cx.typeck_results().expr_ty(arg)
&& peel_mid_ty_refs(arg_ty).1 > 1
{
span_lint_and_help(
cx,
SIZE_OF_REF,
expr.span,
"argument to `std::mem::size_of_val()` is a reference to a reference",
None,
"dereference the argument to `std::mem::size_of_val()` to get the size of the value instead of the size of the reference-type",
);
}
}
}
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