ensure exisentials are copyable

Author: kavon

lib/AST/Module.cpp

@@ -1178,6 +1178,13 @@ ModuleDecl::lookupExistentialConformance(Type type, ProtocolDecl *protocol) {
   if (!protocol->existentialConformsToSelf())
     return ProtocolConformanceRef::forInvalid();
 
+  // All existentials are Copyable.
+  if (protocol->isSpecificProtocol(KnownProtocolKind::Copyable)) {
+    return ProtocolConformanceRef(
+        ctx.getBuiltinConformance(type, protocol, GenericSignature(), {},
+                                  BuiltinConformanceKind::Synthesized));
+  }
+
   auto layout = type->getExistentialLayout();
 
   // Due to an IRGen limitation, witness tables cannot be passed from an

test/Constraints/moveonly_constraints.swift

@@ -164,6 +164,13 @@ func checkStdlibTypes(_ mo: MO) {
   let s: String = "hello \(mo)" // expected-error {{move-only type 'MO' cannot be used with generics yet}}
 }
 
+func copyableExistentials(_ a: Any, _ e1: Error, _ e2: any Error, _ ah: AnyHashable) {
+  takeGeneric(a)
+  takeGeneric(e1)
+  takeGeneric(e2)
+  takeGeneric(ah)
+}
+
 // ensure that associated types can't be witnessed by move-only types
 
 protocol HasType<Ty> {