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) = tcx.impl_trait_ref(item.owner_id) {
  17         let trait_def = tcx.trait_def(trait_ref.def_id);
  18         let unsafe_attr =
  19             impl_.generics.params.iter().find(|p| p.pure_wrt_drop).map(|_| "may_dangle");
  20         match (trait_def.unsafety, unsafe_attr, impl_.unsafety, impl_.polarity) {
  21             (Unsafety::Normal, None, Unsafety::Unsafe, hir::ImplPolarity::Positive) => {
  22                 struct_span_err!(
  23                     tcx.sess,
  24                     tcx.def_span(def_id),
  25                     E0199,
  26                     "implementing the trait `{}` is not unsafe",
  27                     trait_ref.print_only_trait_path()
  28                 )
  29                 .span_suggestion_verbose(
  30                     item.span.with_hi(item.span.lo() + rustc_span::BytePos(7)),
  31                     "remove `unsafe` from this trait implementation",
  32                     "",
  33                     rustc_errors::Applicability::MachineApplicable,
  34                 )
  35                 .emit();
  36             }
  37
  38             (Unsafety::Unsafe, _, Unsafety::Normal, hir::ImplPolarity::Positive) => {
  39                 struct_span_err!(
  40                     tcx.sess,
  41                     tcx.def_span(def_id),
  42                     E0200,
  43                     "the trait `{}` requires an `unsafe impl` declaration",
  44                     trait_ref.print_only_trait_path()
  45                 )
  46                 .note(format!(
  47                     "the trait `{}` enforces invariants that the compiler can't check. \
  48                     Review the trait documentation and make sure this implementation \
  49                     upholds those invariants before adding the `unsafe` keyword",
  50                     trait_ref.print_only_trait_path()
  51                 ))
  52                 .span_suggestion_verbose(
  53                     item.span.shrink_to_lo(),
  54                     "add `unsafe` to this trait implementation",
  55                     "unsafe ",
  56                     rustc_errors::Applicability::MaybeIncorrect,
  57                 )
  58                 .emit();
  59             }
  60
  61             (Unsafety::Normal, Some(attr_name), Unsafety::Normal, hir::ImplPolarity::Positive) => {
  62                 struct_span_err!(
  63                     tcx.sess,
  64                     tcx.def_span(def_id),
  65                     E0569,
  66                     "requires an `unsafe impl` declaration due to `#[{}]` attribute",
  67                     attr_name
  68                 )
  69                 .note(format!(
  70                     "the trait `{}` enforces invariants that the compiler can't check. \
  71                     Review the trait documentation and make sure this implementation \
  72                     upholds those invariants before adding the `unsafe` keyword",
  73                     trait_ref.print_only_trait_path()
  74                 ))
  75                 .span_suggestion_verbose(
  76                     item.span.shrink_to_lo(),
  77                     "add `unsafe` to this trait implementation",
  78                     "unsafe ",
  79                     rustc_errors::Applicability::MaybeIncorrect,
  80                 )
  81                 .emit();
  82             }
  83
  84             (_, _, Unsafety::Unsafe, hir::ImplPolarity::Negative(_)) => {
  85                 // Reported in AST validation
  86                 tcx.sess.delay_span_bug(item.span, "unsafe negative impl");
  87             }
  88             (_, _, Unsafety::Normal, hir::ImplPolarity::Negative(_))
  89             | (Unsafety::Unsafe, _, Unsafety::Unsafe, hir::ImplPolarity::Positive)
  90             | (Unsafety::Normal, Some(_), Unsafety::Unsafe, hir::ImplPolarity::Positive)
  91             | (Unsafety::Normal, None, Unsafety::Normal, _) => {
  92                 // OK
  93             }
  94         }
  95     }
  96 }