1 files changed, 44 insertions, 2 deletions
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
index 17a180a7eb2..ec378c0984f 100644
--- a/compiler/rustc_hir_analysis/src/collect.rs
+++ b/compiler/rustc_hir_analysis/src/collect.rs
@@ -985,8 +985,50 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
 
             no_dups.then_some(list)
         });
-    let do_not_implement_via_object = tcx.has_attr(def_id, sym::rustc_do_not_implement_via_object);
-    let deny_explicit_impl = tcx.has_attr(def_id, sym::rustc_deny_explicit_impl);
+
+    let mut deny_explicit_impl = false;
+    let mut implement_via_object = true;
+    if let Some(attr) = tcx.get_attr(def_id, sym::rustc_deny_explicit_impl) {
+        deny_explicit_impl = true;
+        let mut seen_attr = false;
+        for meta in attr.meta_item_list().iter().flatten() {
+            if let Some(meta) = meta.meta_item()
+                && meta.name_or_empty() == sym::implement_via_object
+                && let Some(lit) = meta.name_value_literal()
+            {
+                if seen_attr {
+                    tcx.sess.span_err(
+                        meta.span,
+                        "duplicated `implement_via_object` meta item",
+                    );
+                }
+                seen_attr = true;
+
+                match lit.symbol {
+                    kw::True => {
+                        implement_via_object = true;
+                    }
+                    kw::False => {
+                        implement_via_object = false;
+                    }
+                    _ => {
+                        tcx.sess.span_err(
+                            meta.span,
+                            format!("unknown literal passed to `implement_via_object` attribute: {}", lit.symbol),
+                        );
+                    }
+                }
+            } else {
+                tcx.sess.span_err(
+                    meta.span(),
+                    format!("unknown meta item passed to `rustc_deny_explicit_impl` {:?}", meta),
+                );
+            }
+        }
+        if !seen_attr {
+            tcx.sess.span_err(attr.span, "missing `implement_via_object` meta item");
+        }
+    }
 
     ty::TraitDef {
         def_id: def_id.to_def_id(),