NCGenerics: omit inverses on invertible protocols

The interface files were still printing inverses on the invertible
protocols, when that's not required. Doing so yielded warnings during
the build because `~Escapable` isn't yet ready for appearing in the
stdlib.

Author: kavon

lib/AST/ASTPrinter.cpp

@@ -1581,9 +1581,16 @@ bestRequirementPrintLocation(ProtocolDecl *proto, const Requirement &req) {
 
 void PrintAST::printInheritedFromRequirementSignature(ProtocolDecl *proto,
                                                       TypeDecl *attachingTo) {
+  unsigned flags = PrintInherited;
+
+  // The invertible protocols themselves do not need to state inverses in their
+  // inheritance clause, because they do not gain any default requirements.
+  if (!proto->getInvertibleProtocolKind())
+    flags |= PrintInverseRequirements;
+
   printRequirementSignature(
       proto, proto->getRequirementSignature(),
-      PrintInherited | PrintInverseRequirements,
+      flags,
       attachingTo);
 }
 

test/ModuleInterface/invertible_protocols.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend %s \
+// RUN:     -swift-version 5 \
+// RUN:     -enable-library-evolution \
+// RUN:     -emit-module -module-name Swift -parse-stdlib \
+// RUN:     -enable-experimental-feature NoncopyableGenerics \
+// RUN:     -o %t/Swift.swiftmodule \
+// RUN:     -emit-module-interface-path %t/Swift.swiftinterface
+
+// RUN: %FileCheck %s < %t/Swift.swiftinterface
+
+// CHECK-DAG: @_marker public protocol Copyable {
+// CHECK-DAG: @_marker public protocol Escapable {
+
+// This test verifies that:
+//   1. When omitted, the an invertible protocol decl gets automatically
+//      synthesized into a module named Swift
+//   2. These protocol decls do not specify inverses in their inheritance clause
+//      when emitted into the interface file.
+
+@_marker public protocol Escapable { }