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