clippy_lints/src/casts/cast_ptr_alignment.rs

   1 use rustc_hir::{Expr, ExprKind, GenericArg};
   2 use rustc_lint::LateContext;
   3 use rustc_middle::ty::{self, Ty};
   4 use rustc_span::symbol::sym;
   5 use rustc_target::abi::LayoutOf;
   6
   7 use if_chain::if_chain;
   8
   9 use crate::utils::{is_hir_ty_cfg_dependant, span_lint};
  10
  11 use super::CAST_PTR_ALIGNMENT;
  12
  13 pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  14     if let ExprKind::Cast(ref cast_expr, cast_to) = expr.kind {
  15         if is_hir_ty_cfg_dependant(cx, cast_to) {
  16             return;
  17         }
  18         let (cast_from, cast_to) = (
  19             cx.typeck_results().expr_ty(cast_expr),
  20             cx.typeck_results().expr_ty(expr),
  21         );
  22         lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
  23     } else if let ExprKind::MethodCall(method_path, _, args, _) = expr.kind {
  24         if_chain! {
  25             if method_path.ident.name == sym!(cast);
  26             if let Some(generic_args) = method_path.args;
  27             if let [GenericArg::Type(cast_to)] = generic_args.args;
  28             // There probably is no obvious reason to do this, just to be consistent with `as` cases.
  29             if !is_hir_ty_cfg_dependant(cx, cast_to);
  30             then {
  31                 let (cast_from, cast_to) =
  32                     (cx.typeck_results().expr_ty(&args[0]), cx.typeck_results().expr_ty(expr));
  33                 lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
  34             }
  35         }
  36     }
  37 }
  38
  39 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
  40     if_chain! {
  41         if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
  42         if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
  43         if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
  44         if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
  45         if from_layout.align.abi < to_layout.align.abi;
  46         // with c_void, we inherently need to trust the user
  47         if !is_c_void(cx, from_ptr_ty.ty);
  48         // when casting from a ZST, we don't know enough to properly lint
  49         if !from_layout.is_zst();
  50         then {
  51             span_lint(
  52                 cx,
  53                 CAST_PTR_ALIGNMENT,
  54                 expr.span,
  55                 &format!(
  56                     "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
  57                     cast_from,
  58                     cast_to,
  59                     from_layout.align.abi.bytes(),
  60                     to_layout.align.abi.bytes(),
  61                 ),
  62             );
  63         }
  64     }
  65 }
  66
  67 /// Check if the given type is either `core::ffi::c_void` or
  68 /// one of the platform specific `libc::<platform>::c_void` of libc.
  69 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
  70     if let ty::Adt(adt, _) = ty.kind() {
  71         let names = cx.get_def_path(adt.did);
  72
  73         if names.is_empty() {
  74             return false;
  75         }
  76         if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
  77             return true;
  78         }
  79     }
  80     false
  81 }