src/tools/clippy/clippy_lints/src/transmute/utils.rs

   1 use rustc_hir::Expr;
   2 use rustc_lint::LateContext;
   3 use rustc_middle::ty::{cast::CastKind, Ty};
   4 use rustc_span::DUMMY_SP;
   5 use rustc_typeck::check::{cast::{self, CastCheckResult}, FnCtxt, Inherited};
   6
   7 // check if the component types of the transmuted collection and the result have different ABI,
   8 // size or alignment
   9 pub(super) fn is_layout_incompatible<'tcx>(cx: &LateContext<'tcx>, from: Ty<'tcx>, to: Ty<'tcx>) -> bool {
  10     if let Ok(from) = cx.tcx.try_normalize_erasing_regions(cx.param_env, from)
  11         && let Ok(to) = cx.tcx.try_normalize_erasing_regions(cx.param_env, to)
  12         && let Ok(from_layout) = cx.tcx.layout_of(cx.param_env.and(from))
  13         && let Ok(to_layout) = cx.tcx.layout_of(cx.param_env.and(to))
  14     {
  15         from_layout.size != to_layout.size || from_layout.align.abi != to_layout.align.abi
  16     } else {
  17         // no idea about layout, so don't lint
  18         false
  19     }
  20 }
  21
  22 /// Check if the type conversion can be expressed as a pointer cast, instead of
  23 /// a transmute. In certain cases, including some invalid casts from array
  24 /// references to pointers, this may cause additional errors to be emitted and/or
  25 /// ICE error messages. This function will panic if that occurs.
  26 pub(super) fn can_be_expressed_as_pointer_cast<'tcx>(
  27     cx: &LateContext<'tcx>,
  28     e: &'tcx Expr<'_>,
  29     from_ty: Ty<'tcx>,
  30     to_ty: Ty<'tcx>,
  31 ) -> bool {
  32     use CastKind::{AddrPtrCast, ArrayPtrCast, FnPtrAddrCast, FnPtrPtrCast, PtrAddrCast, PtrPtrCast};
  33     matches!(
  34         check_cast(cx, e, from_ty, to_ty),
  35         Some(PtrPtrCast | PtrAddrCast | AddrPtrCast | ArrayPtrCast | FnPtrPtrCast | FnPtrAddrCast)
  36     )
  37 }
  38
  39 /// If a cast from `from_ty` to `to_ty` is valid, returns an Ok containing the kind of
  40 /// the cast. In certain cases, including some invalid casts from array references
  41 /// to pointers, this may cause additional errors to be emitted and/or ICE error
  42 /// messages. This function will panic if that occurs.
  43 fn check_cast<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>, from_ty: Ty<'tcx>, to_ty: Ty<'tcx>) -> Option<CastKind> {
  44     let hir_id = e.hir_id;
  45     let local_def_id = hir_id.owner;
  46
  47     Inherited::build(cx.tcx, local_def_id).enter(|inherited| {
  48         let fn_ctxt = FnCtxt::new(&inherited, cx.param_env, hir_id);
  49
  50         // If we already have errors, we can't be sure we can pointer cast.
  51         assert!(
  52             !fn_ctxt.errors_reported_since_creation(),
  53             "Newly created FnCtxt contained errors"
  54         );
  55
  56         if let CastCheckResult::Deferred(check) = cast::check_cast(
  57             &fn_ctxt, e, from_ty, to_ty,
  58             // We won't show any error to the user, so we don't care what the span is here.
  59             DUMMY_SP, DUMMY_SP,
  60         ) {
  61             let res = check.do_check(&fn_ctxt);
  62
  63             // do_check's documentation says that it might return Ok and create
  64             // errors in the fcx instead of returning Err in some cases. Those cases
  65             // should be filtered out before getting here.
  66             assert!(
  67                 !fn_ctxt.errors_reported_since_creation(),
  68                 "`fn_ctxt` contained errors after cast check!"
  69             );
  70
  71             res.ok()
  72         } else {
  73             None
  74         }
  75     })
  76 }