Stop opening the "bound" generic signature of an opaque type declaration.

Creation of the "bound" generic signature isn't possible with interface
types or type variables, so open up the opaque interface signature
instead and separately bind the outer type parameters as appropriate.

Author: DougGregor

lib/Sema/ConstraintSystem.cpp

@@ -837,7 +837,8 @@ Type ConstraintSystem::openType(Type type, OpenedTypeMap &replacements) {
 
 Type ConstraintSystem::openOpaqueType(OpaqueTypeArchetypeType *opaque,
                                       ConstraintLocatorBuilder locator) {
-  auto opaqueLocatorKey = getOpenOpaqueLocator(locator, opaque->getDecl());
+  auto opaqueDecl = opaque->getDecl();
+  auto opaqueLocatorKey = getOpenOpaqueLocator(locator, opaqueDecl);
 
   // If we have already opened this opaque type, look in the known set of
   // replacements.
@@ -858,9 +859,22 @@ Type ConstraintSystem::openOpaqueType(OpaqueTypeArchetypeType *opaque,
   // corresponding to the underlying type should be the constraints on the
   // underlying return type.
   auto opaqueLocator = locator.withPathElement(
-      LocatorPathElt::OpenedOpaqueArchetype(opaque->getDecl()));
+      LocatorPathElt::OpenedOpaqueArchetype(opaqueDecl));
   OpenedTypeMap replacements;
-  openGeneric(DC, opaque->getBoundSignature(), opaqueLocator, replacements);
+  openGeneric(DC, opaqueDecl->getOpaqueInterfaceGenericSignature(),
+              opaqueLocator, replacements);
+
+  // If there is an outer generic signature, bind the outer parameters based
+  // on the substitutions in the opaque type.
+  auto subs = opaque->getSubstitutions();
+  if (auto genericSig = subs.getGenericSignature()) {
+    for (auto *genericParamPtr : genericSig.getGenericParams()) {
+      Type genericParam(genericParamPtr);
+      addConstraint(
+          ConstraintKind::Bind, openType(genericParam, replacements),
+          genericParam.subst(subs), opaqueLocator);
+    }
+  }
 
   recordOpenedTypes(opaqueLocatorKey, replacements);