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use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::{get_parent_expr, meets_msrv, msrvs};
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, GenericArg, QPath};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::{self, Ty};
use rustc_semver::RustcVersion;
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for uses of `std::mem::size_of::<T>() * 8` when
/// `T::BITS` is available.
///
/// ### Why is this bad?
/// Can be written as the shorter `T::BITS`.
///
/// ### Example
/// ```rust
/// std::mem::size_of::<usize>() * 8;
/// ```
/// Use instead:
/// ```rust
/// usize::BITS as usize;
/// ```
#[clippy::version = "1.60.0"]
pub MANUAL_BITS,
style,
"manual implementation of `size_of::<T>() * 8` can be simplified with `T::BITS`"
}
#[derive(Clone)]
pub struct ManualBits {
msrv: Option<RustcVersion>,
}
impl ManualBits {
#[must_use]
pub fn new(msrv: Option<RustcVersion>) -> Self {
Self { msrv }
}
}
impl_lint_pass!(ManualBits => [MANUAL_BITS]);
impl<'tcx> LateLintPass<'tcx> for ManualBits {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
if !meets_msrv(self.msrv, msrvs::MANUAL_BITS) {
return;
}
if_chain! {
if let ExprKind::Binary(bin_op, left_expr, right_expr) = expr.kind;
if let BinOpKind::Mul = &bin_op.node;
if let Some((real_ty, resolved_ty, other_expr)) = get_one_size_of_ty(cx, left_expr, right_expr);
if matches!(resolved_ty.kind(), ty::Int(_) | ty::Uint(_));
if let ExprKind::Lit(lit) = &other_expr.kind;
if let LitKind::Int(8, _) = lit.node;
then {
let mut app = Applicability::MachineApplicable;
let ty_snip = snippet_with_applicability(cx, real_ty.span, "..", &mut app);
let sugg = create_sugg(cx, expr, format!("{ty_snip}::BITS"));
span_lint_and_sugg(
cx,
MANUAL_BITS,
expr.span,
"usage of `mem::size_of::<T>()` to obtain the size of `T` in bits",
"consider using",
sugg,
app,
);
}
}
}
extract_msrv_attr!(LateContext);
}
fn get_one_size_of_ty<'tcx>(
cx: &LateContext<'tcx>,
expr1: &'tcx Expr<'_>,
expr2: &'tcx Expr<'_>,
) -> Option<(&'tcx rustc_hir::Ty<'tcx>, Ty<'tcx>, &'tcx Expr<'tcx>)> {
match (get_size_of_ty(cx, expr1), get_size_of_ty(cx, expr2)) {
(Some((real_ty, resolved_ty)), None) => Some((real_ty, resolved_ty, expr2)),
(None, Some((real_ty, resolved_ty))) => Some((real_ty, resolved_ty, expr1)),
_ => None,
}
}
fn get_size_of_ty<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<(&'tcx rustc_hir::Ty<'tcx>, Ty<'tcx>)> {
if_chain! {
if let ExprKind::Call(count_func, _func_args) = expr.kind;
if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
if let QPath::Resolved(_, count_func_path) = count_func_qpath;
if let Some(segment_zero) = count_func_path.segments.get(0);
if let Some(args) = segment_zero.args;
if let Some(GenericArg::Type(real_ty)) = args.args.get(0);
if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
if cx.tcx.is_diagnostic_item(sym::mem_size_of, def_id);
then {
cx.typeck_results().node_substs(count_func.hir_id).types().next().map(|resolved_ty| (real_ty, resolved_ty))
} else {
None
}
}
}
fn create_sugg(cx: &LateContext<'_>, expr: &Expr<'_>, base_sugg: String) -> String {
if let Some(parent_expr) = get_parent_expr(cx, expr) {
if is_ty_conversion(parent_expr) {
return base_sugg;
}
// These expressions have precedence over casts, the suggestion therefore
// needs to be wrapped into parentheses
match parent_expr.kind {
ExprKind::Unary(..) | ExprKind::AddrOf(..) | ExprKind::MethodCall(..) => {
return format!("({base_sugg} as usize)");
},
_ => {},
}
}
format!("{base_sugg} as usize")
}
fn is_ty_conversion(expr: &Expr<'_>) -> bool {
if let ExprKind::Cast(..) = expr.kind {
true
} else if let ExprKind::MethodCall(path, [_], _) = expr.kind
&& path.ident.name == rustc_span::sym::try_into
{
// This is only called for `usize` which implements `TryInto`. Therefore,
// we don't have to check here if `self` implements the `TryInto` trait.
true
} else {
false
}
}
|
