Combine instantiation context of field initializer with context of class.

[sepavloff]

Summary

Inclass initializer is instantiated in its own LocalInstantiationScope. It
causes problems when instantiating local classes - when instantiation scope
is searched for DeclContext of the field, the search fails. As a solution,
the instantiation scope of field initializer is combined with its outer
scope.

This patch fixes PR23194.

[rsmith]

LGTM

cfe/trunk/lib/Sema/SemaTemplateInstantiate.cpp

if (Inst.isInvalid())
     return true;
 
   // Enter the scope of this instantiation. We don't use PushDeclContext because
   // we don't have a scope.
   ContextRAII SavedContext(*this, Instantiation->getParent());
   EnterExpressionEvaluationContext EvalContext(*this,
                                                Sema::PotentiallyEvaluated);
 
-  LocalInstantiationScope Scope(*this);
+  LocalInstantiationScope Scope(*this, true);
 
   // Instantiate the initializer.
   ActOnStartCXXInClassMemberInitializer();
   CXXThisScopeRAII ThisScope(*this, Instantiation->getParent(), /*TypeQuals=*/0);
 
   ExprResult NewInit = SubstInitializer(OldInit, TemplateArgs,
                                         /*CXXDirectInit=*/false);
   Expr *Init = NewInit.get();

cfe/trunk/test/SemaTemplate/instantiate-local-class.cpp

 void F() {
   struct A : C<X> {};
 }
 
 struct B {
   void f() { F<int>(); }
 };
 }
+
+namespace PR23194 {
+  struct X {
+    int operator()() const { return 0; }
+  };
+  struct Y {
+    Y(int) {}
+  };
+  template <bool = true> int make_seed_pair() noexcept {
+    struct state_t {
+      X x;
+      Y y{x()};
+    };
+    return 0;
+  }
+  int func() {
+    return make_seed_pair();
+  }
+}