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use clippy_utils::diagnostics::span_lint;
use clippy_utils::ty::is_c_void;
use clippy_utils::{get_parent_expr, is_hir_ty_cfg_dependant, match_any_def_paths, paths};
use rustc_hir::{Expr, ExprKind, GenericArg};
use rustc_lint::LateContext;
use rustc_middle::ty::layout::LayoutOf;
use rustc_middle::ty::{self, Ty};
use super::CAST_PTR_ALIGNMENT;
pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
if let ExprKind::Cast(cast_expr, cast_to) = expr.kind {
if is_hir_ty_cfg_dependant(cx, cast_to) {
return;
}
let (cast_from, cast_to) = (
cx.typeck_results().expr_ty(cast_expr),
cx.typeck_results().expr_ty(expr),
);
lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
} else if let ExprKind::MethodCall(method_path, self_arg, ..) = &expr.kind {
if method_path.ident.name == sym!(cast)
&& let Some(generic_args) = method_path.args
&& let [GenericArg::Type(cast_to)] = generic_args.args
// There probably is no obvious reason to do this, just to be consistent with `as` cases.
&& !is_hir_ty_cfg_dependant(cx, cast_to)
{
let (cast_from, cast_to) =
(cx.typeck_results().expr_ty(self_arg), cx.typeck_results().expr_ty(expr));
lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
}
}
}
fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
if let ty::RawPtr(from_ptr_ty) = &cast_from.kind()
&& let ty::RawPtr(to_ptr_ty) = &cast_to.kind()
&& let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty)
&& let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty)
&& from_layout.align.abi < to_layout.align.abi
// with c_void, we inherently need to trust the user
&& !is_c_void(cx, from_ptr_ty.ty)
// when casting from a ZST, we don't know enough to properly lint
&& !from_layout.is_zst()
&& !is_used_as_unaligned(cx, expr)
{
span_lint(
cx,
CAST_PTR_ALIGNMENT,
expr.span,
&format!(
"casting from `{cast_from}` to a more-strictly-aligned pointer (`{cast_to}`) ({} < {} bytes)",
from_layout.align.abi.bytes(),
to_layout.align.abi.bytes(),
),
);
}
}
fn is_used_as_unaligned(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
let Some(parent) = get_parent_expr(cx, e) else {
return false;
};
match parent.kind {
ExprKind::MethodCall(name, self_arg, ..) if self_arg.hir_id == e.hir_id => {
if matches!(name.ident.as_str(), "read_unaligned" | "write_unaligned")
&& let Some(def_id) = cx.typeck_results().type_dependent_def_id(parent.hir_id)
&& let Some(def_id) = cx.tcx.impl_of_method(def_id)
&& cx.tcx.type_of(def_id).subst_identity().is_unsafe_ptr()
{
true
} else {
false
}
},
ExprKind::Call(func, [arg, ..]) if arg.hir_id == e.hir_id => {
static PATHS: &[&[&str]] = &[
paths::PTR_READ_UNALIGNED.as_slice(),
paths::PTR_WRITE_UNALIGNED.as_slice(),
paths::PTR_UNALIGNED_VOLATILE_LOAD.as_slice(),
paths::PTR_UNALIGNED_VOLATILE_STORE.as_slice(),
];
if let ExprKind::Path(path) = &func.kind
&& let Some(def_id) = cx.qpath_res(path, func.hir_id).opt_def_id()
&& match_any_def_paths(cx, def_id, PATHS).is_some()
{
true
} else {
false
}
},
_ => false,
}
}
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