2 files changed, 14 insertions, 0 deletions
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 7a29f8c9fbd..fe76d9e0b64 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -1118,6 +1118,10 @@ pub trait ResolverExpand {
         trait_def_id: DefId,
         impl_def_id: LocalDefId,
     ) -> Result<Vec<(Ident, Option<Ident>)>, Indeterminate>;
+
+    /// Record the name of an opaque `Ty::ImplTrait` pre-expansion so that it can be used
+    /// to generate an item name later that does not reference placeholder macros.
+    fn insert_impl_trait_name(&mut self, id: NodeId, name: Symbol);
 }
 
 pub trait LintStoreExpand {
diff --git a/compiler/rustc_expand/src/expand.rs b/compiler/rustc_expand/src/expand.rs
index 0474413e762..2de09aa1a28 100644
--- a/compiler/rustc_expand/src/expand.rs
+++ b/compiler/rustc_expand/src/expand.rs
@@ -1778,6 +1778,16 @@ impl InvocationCollectorNode for ast::Ty {
         fragment.make_ty()
     }
     fn walk(&mut self, collector: &mut InvocationCollector<'_, '_>) {
+        // Save the pre-expanded name of this `ImplTrait`, so that later when defining
+        // an APIT we use a name that doesn't have any placeholder fragments in it.
+        if let ast::TyKind::ImplTrait(..) = self.kind {
+            // HACK: pprust breaks strings with newlines when the type
+            // gets too long. We don't want these to show up in compiler
+            // output or built artifacts, so replace them here...
+            // Perhaps we should instead format APITs more robustly.
+            let name = Symbol::intern(&pprust::ty_to_string(self).replace('\n', " "));
+            collector.cx.resolver.insert_impl_trait_name(self.id, name);
+        }
         walk_ty(collector, self)
     }
     fn is_mac_call(&self) -> bool {