src/tools/clippy/clippy_lints/src/casts/cast_ptr_alignment.rs

   1 use clippy_utils::diagnostics::span_lint;
   2 use clippy_utils::ty::is_c_void;
   3 use clippy_utils::{get_parent_expr, is_hir_ty_cfg_dependant, match_any_def_paths, paths};
   4 use rustc_hir::{Expr, ExprKind, GenericArg};
   5 use rustc_lint::LateContext;
   6 use rustc_middle::ty::layout::LayoutOf;
   7 use rustc_middle::ty::{self, Ty};
   8
   9 use super::CAST_PTR_ALIGNMENT;
  10
  11 pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>) {
  12     if let ExprKind::Cast(cast_expr, cast_to) = expr.kind {
  13         if is_hir_ty_cfg_dependant(cx, cast_to) {
  14             return;
  15         }
  16         let (cast_from, cast_to) = (
  17             cx.typeck_results().expr_ty(cast_expr),
  18             cx.typeck_results().expr_ty(expr),
  19         );
  20         lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
  21     } else if let ExprKind::MethodCall(method_path, self_arg, ..) = &expr.kind {
  22         if method_path.ident.name == sym!(cast)
  23             && let Some(generic_args) = method_path.args
  24             && let [GenericArg::Type(cast_to)] = generic_args.args
  25             // There probably is no obvious reason to do this, just to be consistent with `as` cases.
  26             && !is_hir_ty_cfg_dependant(cx, cast_to)
  27         {
  28             let (cast_from, cast_to) =
  29                 (cx.typeck_results().expr_ty(self_arg), cx.typeck_results().expr_ty(expr));
  30             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
  31         }
  32     }
  33 }
  34
  35 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
  36     if let ty::RawPtr(from_ptr_ty) = &cast_from.kind()
  37         && let ty::RawPtr(to_ptr_ty) = &cast_to.kind()
  38         && let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty)
  39         && let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty)
  40         && from_layout.align.abi < to_layout.align.abi
  41         // with c_void, we inherently need to trust the user
  42         && !is_c_void(cx, from_ptr_ty.ty)
  43         // when casting from a ZST, we don't know enough to properly lint
  44         && !from_layout.is_zst()
  45         && !is_used_as_unaligned(cx, expr)
  46     {
  47         span_lint(
  48             cx,
  49             CAST_PTR_ALIGNMENT,
  50             expr.span,
  51             &format!(
  52                 "casting from `{cast_from}` to a more-strictly-aligned pointer (`{cast_to}`) ({} < {} bytes)",
  53                 from_layout.align.abi.bytes(),
  54                 to_layout.align.abi.bytes(),
  55             ),
  56         );
  57     }
  58 }
  59
  60 fn is_used_as_unaligned(cx: &LateContext<'_>, e: &Expr<'_>) -> bool {
  61     let Some(parent) = get_parent_expr(cx, e) else {
  62         return false;
  63     };
  64     match parent.kind {
  65         ExprKind::MethodCall(name, self_arg, ..) if self_arg.hir_id == e.hir_id => {
  66             if matches!(name.ident.as_str(), "read_unaligned" | "write_unaligned")
  67                 && let Some(def_id) = cx.typeck_results().type_dependent_def_id(parent.hir_id)
  68                 && let Some(def_id) = cx.tcx.impl_of_method(def_id)
  69                 && cx.tcx.type_of(def_id).subst_identity().is_unsafe_ptr()
  70             {
  71                 true
  72             } else {
  73                 false
  74             }
  75         },
  76         ExprKind::Call(func, [arg, ..]) if arg.hir_id == e.hir_id => {
  77             static PATHS: &[&[&str]] = &[
  78                 paths::PTR_READ_UNALIGNED.as_slice(),
  79                 paths::PTR_WRITE_UNALIGNED.as_slice(),
  80                 paths::PTR_UNALIGNED_VOLATILE_LOAD.as_slice(),
  81                 paths::PTR_UNALIGNED_VOLATILE_STORE.as_slice(),
  82             ];
  83             if let ExprKind::Path(path) = &func.kind
  84                 && let Some(def_id) = cx.qpath_res(path, func.hir_id).opt_def_id()
  85                 && match_any_def_paths(cx, def_id, PATHS).is_some()
  86             {
  87                 true
  88             } else {
  89                 false
  90             }
  91         },
  92         _ => false,
  93     }
  94 }