compiler/rustc_hir_analysis/src/coherence/unsafety.rs

   1 //! Unsafety checker: every impl either implements a trait defined in this
   2 //! crate or pertains to a type defined in this crate.
   3
   4 use rustc_errors::struct_span_err;
   5 use rustc_hir as hir;
   6 use rustc_hir::def::DefKind;
   7 use rustc_hir::Unsafety;
   8 use rustc_middle::ty::TyCtxt;
   9 use rustc_span::def_id::LocalDefId;
  10
  11 pub(super) fn check_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
  12     debug_assert!(matches!(tcx.def_kind(def_id), DefKind::Impl));
  13     let item = tcx.hir().expect_item(def_id);
  14     let hir::ItemKind::Impl(ref impl_) = item.kind else { bug!() };
  15
  16     if let Some(trait_ref) =
  17         tcx.bound_impl_trait_ref(item.owner_id.to_def_id()).map(|t| t.subst_identity())
  18     {
  19         let trait_def = tcx.trait_def(trait_ref.def_id);
  20         let unsafe_attr =
  21             impl_.generics.params.iter().find(|p| p.pure_wrt_drop).map(|_| "may_dangle");
  22         match (trait_def.unsafety, unsafe_attr, impl_.unsafety, impl_.polarity) {
  23             (Unsafety::Normal, None, Unsafety::Unsafe, hir::ImplPolarity::Positive) => {
  24                 struct_span_err!(
  25                     tcx.sess,
  26                     tcx.def_span(def_id),
  27                     E0199,
  28                     "implementing the trait `{}` is not unsafe",
  29                     trait_ref.print_only_trait_path()
  30                 )
  31                 .span_suggestion_verbose(
  32                     item.span.with_hi(item.span.lo() + rustc_span::BytePos(7)),
  33                     "remove `unsafe` from this trait implementation",
  34                     "",
  35                     rustc_errors::Applicability::MachineApplicable,
  36                 )
  37                 .emit();
  38             }
  39
  40             (Unsafety::Unsafe, _, Unsafety::Normal, hir::ImplPolarity::Positive) => {
  41                 struct_span_err!(
  42                     tcx.sess,
  43                     tcx.def_span(def_id),
  44                     E0200,
  45                     "the trait `{}` requires an `unsafe impl` declaration",
  46                     trait_ref.print_only_trait_path()
  47                 )
  48                 .note(format!(
  49                     "the trait `{}` enforces invariants that the compiler can't check. \
  50                     Review the trait documentation and make sure this implementation \
  51                     upholds those invariants before adding the `unsafe` keyword",
  52                     trait_ref.print_only_trait_path()
  53                 ))
  54                 .span_suggestion_verbose(
  55                     item.span.shrink_to_lo(),
  56                     "add `unsafe` to this trait implementation",
  57                     "unsafe ",
  58                     rustc_errors::Applicability::MaybeIncorrect,
  59                 )
  60                 .emit();
  61             }
  62
  63             (Unsafety::Normal, Some(attr_name), Unsafety::Normal, hir::ImplPolarity::Positive) => {
  64                 struct_span_err!(
  65                     tcx.sess,
  66                     tcx.def_span(def_id),
  67                     E0569,
  68                     "requires an `unsafe impl` declaration due to `#[{}]` attribute",
  69                     attr_name
  70                 )
  71                 .note(format!(
  72                     "the trait `{}` enforces invariants that the compiler can't check. \
  73                     Review the trait documentation and make sure this implementation \
  74                     upholds those invariants before adding the `unsafe` keyword",
  75                     trait_ref.print_only_trait_path()
  76                 ))
  77                 .span_suggestion_verbose(
  78                     item.span.shrink_to_lo(),
  79                     "add `unsafe` to this trait implementation",
  80                     "unsafe ",
  81                     rustc_errors::Applicability::MaybeIncorrect,
  82                 )
  83                 .emit();
  84             }
  85
  86             (_, _, Unsafety::Unsafe, hir::ImplPolarity::Negative(_)) => {
  87                 // Reported in AST validation
  88                 tcx.sess.delay_span_bug(item.span, "unsafe negative impl");
  89             }
  90             (_, _, Unsafety::Normal, hir::ImplPolarity::Negative(_))
  91             | (Unsafety::Unsafe, _, Unsafety::Unsafe, hir::ImplPolarity::Positive)
  92             | (Unsafety::Normal, Some(_), Unsafety::Unsafe, hir::ImplPolarity::Positive)
  93             | (Unsafety::Normal, None, Unsafety::Normal, _) => {
  94                 // OK
  95             }
  96         }
  97     }
  98 }