Demangler: fix substitutions for OpaqueType in the remangler.

rdar://problem/50132625

Author: eeckstein

lib/Demangling/Remangler.cpp

@@ -2341,6 +2341,9 @@ void Remangler::mangleOpaqueReturnTypeOf(Node *node) {
   Buffer << "QO";
 }
 void Remangler::mangleOpaqueType(Node *node) {
+  SubstitutionEntry entry;
+  if (trySubstitution(node, entry)) return;
+
   mangle(node->getChild(0));
   auto boundGenerics = node->getChild(2);
   for (unsigned i = 0; i < boundGenerics->getNumChildren(); ++i) {
@@ -2355,6 +2358,8 @@ void Remangler::mangleOpaqueType(Node *node) {
   }
   Buffer << "Qo";
   mangleIndex(node->getChild(1)->getIndex());
+
+  addSubstitution(entry);
 }
 void Remangler::mangleAccessorFunctionReference(Node *node) {
   unreachable("can't remangle");

test/Demangle/Inputs/manglings.txt

@@ -325,6 +325,7 @@ _$S3BBBBf0602365061_ ---> _$S3BBBBf0602365061_
 _$S3BBBBi0602365061_ ---> _$S3BBBBi0602365061_
 _$S3BBBBv0602365061_ ---> _$S3BBBBv0602365061_
 _T0lxxxmmmTk ---> _T0lxxxmmmTk
+$s4test3fooV4blahyAA1SV1fQryFQOy_Qo_AHF ---> test.foo.blah(<<opaque return type of test.S.f() -> some>>.0) -> <<opaque return type of test.S.f() -> some>>.0
 $S3nix8MystructV1xACyxGx_tcfc7MyaliasL_ayx__GD ---> Myalias #1 in nix.Mystruct<A>.init(x: A) -> nix.Mystruct<A>
 $S3nix7MyclassCfd7MyaliasL_ayx__GD ---> Myalias #1 in nix.Myclass<A>.deinit
 $S3nix8MystructVyS2icig7MyaliasL_ayx__GD ---> Myalias #1 in nix.Mystruct<A>.subscript.getter : (Swift.Int) -> Swift.Int