1 files changed, 66 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/coherence/unsafety.rs b/compiler/rustc_typeck/src/coherence/unsafety.rs
new file mode 100644
index 000000000..e45fb5fe4
--- /dev/null
+++ b/compiler/rustc_typeck/src/coherence/unsafety.rs
@@ -0,0 +1,66 @@
+//! Unsafety checker: every impl either implements a trait defined in this
+//! crate or pertains to a type defined in this crate.
+
+use rustc_errors::struct_span_err;
+use rustc_hir as hir;
+use rustc_hir::def::DefKind;
+use rustc_hir::Unsafety;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::def_id::LocalDefId;
+
+pub(super) fn check_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
+    debug_assert!(matches!(tcx.def_kind(def_id), DefKind::Impl));
+    let item = tcx.hir().expect_item(def_id);
+    let hir::ItemKind::Impl(ref impl_) = item.kind else { bug!() };
+
+    if let Some(trait_ref) = tcx.impl_trait_ref(item.def_id) {
+        let trait_def = tcx.trait_def(trait_ref.def_id);
+        let unsafe_attr =
+            impl_.generics.params.iter().find(|p| p.pure_wrt_drop).map(|_| "may_dangle");
+        match (trait_def.unsafety, unsafe_attr, impl_.unsafety, impl_.polarity) {
+            (Unsafety::Normal, None, Unsafety::Unsafe, hir::ImplPolarity::Positive) => {
+                struct_span_err!(
+                    tcx.sess,
+                    item.span,
+                    E0199,
+                    "implementing the trait `{}` is not unsafe",
+                    trait_ref.print_only_trait_path()
+                )
+                .emit();
+            }
+
+            (Unsafety::Unsafe, _, Unsafety::Normal, hir::ImplPolarity::Positive) => {
+                struct_span_err!(
+                    tcx.sess,
+                    item.span,
+                    E0200,
+                    "the trait `{}` requires an `unsafe impl` declaration",
+                    trait_ref.print_only_trait_path()
+                )
+                .emit();
+            }
+
+            (Unsafety::Normal, Some(attr_name), Unsafety::Normal, hir::ImplPolarity::Positive) => {
+                struct_span_err!(
+                    tcx.sess,
+                    item.span,
+                    E0569,
+                    "requires an `unsafe impl` declaration due to `#[{}]` attribute",
+                    attr_name
+                )
+                .emit();
+            }
+
+            (_, _, Unsafety::Unsafe, hir::ImplPolarity::Negative(_)) => {
+                // Reported in AST validation
+                tcx.sess.delay_span_bug(item.span, "unsafe negative impl");
+            }
+            (_, _, Unsafety::Normal, hir::ImplPolarity::Negative(_))
+            | (Unsafety::Unsafe, _, Unsafety::Unsafe, hir::ImplPolarity::Positive)
+            | (Unsafety::Normal, Some(_), Unsafety::Unsafe, hir::ImplPolarity::Positive)
+            | (Unsafety::Normal, None, Unsafety::Normal, _) => {
+                // OK
+            }
+        }
+    }
+}