Index: include/clang/Basic/VirtualFileSystem.h
===================================================================
--- include/clang/Basic/VirtualFileSystem.h
+++ include/clang/Basic/VirtualFileSystem.h
@@ -319,19 +319,23 @@
   explicit InMemoryFileSystem(bool UseNormalizedPaths = true);
   ~InMemoryFileSystem() override;
 
-  /// Add a buffer to the VFS with a path. The VFS owns the buffer.
-  /// If present, User, Group, Type and Perms apply to the newly-created file.
-  /// \return true if the file was successfully added, false if the file already
-  /// exists in the file system with different contents.
+  /// Add a file containing a buffer or a directory to the VFS with a
+  /// path. The VFS owns the buffer.  If present, User, Group, Type
+  /// and Perms apply to the newly-created file or directory.
+  /// \return true if the file or directory was successfully added,
+  /// false if the file or directory already exists in the file system with
+  /// different contents.
   bool addFile(const Twine &Path, time_t ModificationTime,
                std::unique_ptr<llvm::MemoryBuffer> Buffer,
                Optional<uint32_t> User = None, Optional<uint32_t> Group = None,
                Optional<llvm::sys::fs::file_type> Type = None,
                Optional<llvm::sys::fs::perms> Perms = None);
   /// Add a buffer to the VFS with a path. The VFS does not own the buffer.
-  /// If present, User, Group, Type and Perms apply to the newly-created file.
-  /// \return true if the file was successfully added, false if the file already
-  /// exists in the file system with different contents.
+  /// If present, User, Group, Type and Perms apply to the newly-created file
+  /// or directory.
+  /// \return true if the file or directory was successfully added,
+  /// false if the file or directory already exists in the file system with
+  /// different contents.
   bool addFileNoOwn(const Twine &Path, time_t ModificationTime,
                     llvm::MemoryBuffer *Buffer,
                     Optional<uint32_t> User = None,
Index: lib/Basic/VirtualFileSystem.cpp
===================================================================
--- lib/Basic/VirtualFileSystem.cpp
+++ lib/Basic/VirtualFileSystem.cpp
@@ -527,13 +527,19 @@
     ++I;
     if (!Node) {
       if (I == E) {
-        // End of the path, create a new file.
+        // End of the path, create a new file or directory.
         Status Stat(P.str(), getNextVirtualUniqueID(),
                     llvm::sys::toTimePoint(ModificationTime), ResolvedUser,
                     ResolvedGroup, Buffer->getBufferSize(), ResolvedType,
                     ResolvedPerms);
-        Dir->addChild(Name, llvm::make_unique<detail::InMemoryFile>(
-                                std::move(Stat), std::move(Buffer)));
+        std::unique_ptr<detail::InMemoryNode> child;
+        if (ResolvedType == sys::fs::file_type::directory_file) {
+          child.reset(new detail::InMemoryDirectory(std::move(Stat)));
+        } else {
+          child.reset(new detail::InMemoryFile(std::move(Stat),
+                                               std::move(Buffer)));
+        }
+        Dir->addChild(Name, std::move(child));
         return true;
       }
 
Index: unittests/Basic/VirtualFileSystemTest.cpp
===================================================================
--- unittests/Basic/VirtualFileSystemTest.cpp
+++ unittests/Basic/VirtualFileSystemTest.cpp
@@ -829,6 +829,19 @@
             Stat->getPermissions());
 }
 
+TEST_F(InMemoryFileSystemTest, AddDirectoryThenAddChild) {
+  FS.addFile("/a", 0, MemoryBuffer::getMemBuffer(""), /*User=*/None,
+             /*Group=*/None, sys::fs::file_type::directory_file);
+  FS.addFile("/a/b", 0, MemoryBuffer::getMemBuffer("abc"), /*User=*/None,
+             /*Group=*/None, sys::fs::file_type::regular_file);
+  auto Stat = FS.status("/a");
+  ASSERT_FALSE(Stat.getError()) << Stat.getError() << "\n" << FS.toString();
+  ASSERT_TRUE(Stat->isDirectory());
+  Stat = FS.status("/a/b");
+  ASSERT_FALSE(Stat.getError()) << Stat.getError() << "\n" << FS.toString();
+  ASSERT_TRUE(Stat->isRegularFile());
+}
+
 // NOTE: in the tests below, we use '//root/' as our root directory, since it is
 // a legal *absolute* path on Windows as well as *nix.
 class VFSFromYAMLTest : public ::testing::Test {