Take care another assert:

struct A {
  struct B;
};

struct A::B {
  void m() {} // Assertion failed: getContainingDC(DC) == CurContext && "The next DeclContext should be lexically contained in the current one."
};

Introduce DeclContext::getLexicalParent which may be different from DeclContext::getParent when nested-names are involved, e.g:

   namespace A {
      struct S;
   }
   struct A::S {}; // getParent() == namespace 'A'
                   // getLexicalParent() == translation unit


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59650 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/DeclBase.cpp b/lib/AST/DeclBase.cpp
index 88d9a20..c0655cf 100644
--- a/lib/AST/DeclBase.cpp
+++ b/lib/AST/DeclBase.cpp
@@ -361,3 +361,12 @@
   else
     return NULL;
 }
+
+const DeclContext *DeclContext::getLexicalParent() const {
+  if (const ScopedDecl *SD = dyn_cast<ScopedDecl>(this))
+    return SD->getLexicalDeclContext();
+  else if (const BlockDecl *BD = dyn_cast<BlockDecl>(this))
+    return BD->getParentContext();
+  else
+    return NULL;
+}