[CSSolver] Add recorded pack expansion environments to solutions

Fixes a bug where only pack environments created during constraint
would be usable during solution application, everything else would
create a new environment that would produce pack elements with new
UUIDs which cases issues during SILGen.

Author: xedin

lib/Sema/CSSolver.cpp

@@ -213,6 +213,10 @@ Solution ConstraintSystem::finalize() {
     solution.ImplicitCallAsFunctionRoots.insert(implicitRoot);
   }
 
+  for (const auto &env : PackExpansionEnvironments) {
+    solution.PackExpansionEnvironments.insert(env);
+  }
+
   return solution;
 }
 

lib/Sema/TypeCheckConstraints.cpp

@@ -1578,6 +1578,16 @@ void ConstraintSystem::print(raw_ostream &out) const {
     }
   }
 
+  if (!PackExpansionEnvironments.empty()) {
+    out.indent(indent) << "Pack Expansion Environments:\n";
+    for (const auto &env : PackExpansionEnvironments) {
+      out.indent(indent + 2);
+      env.first->dump(&getASTContext().SourceMgr, out);
+      out << " = (" << env.second.first << ", "
+          << env.second.second->getString(PO) << ")" << '\n';
+    }
+  }
+
   if (!DefaultedConstraints.empty()) {
     out.indent(indent) << "Defaulted constraints:\n";
     interleave(DefaultedConstraints, [&](ConstraintLocator *locator) {