Index: clang-tools-extra/trunk/clangd/ClangdServer.h
===================================================================
--- clang-tools-extra/trunk/clangd/ClangdServer.h
+++ clang-tools-extra/trunk/clangd/ClangdServer.h
@@ -43,20 +43,22 @@
 Position offsetToPosition(StringRef Code, size_t Offset);
 
 /// A tag supplied by the FileSytemProvider.
-typedef int VFSTag;
+typedef std::string VFSTag;
 
 /// A value of an arbitrary type and VFSTag that was supplied by the
 /// FileSystemProvider when this value was computed.
 template <class T> class Tagged {
 public:
   template <class U>
-  Tagged(U &&Value, VFSTag Tag) : Value(std::forward<U>(Value)), Tag(Tag) {}
+  Tagged(U &&Value, VFSTag Tag)
+      : Value(std::forward<U>(Value)), Tag(std::move(Tag)) {}
 
   template <class U>
   Tagged(const Tagged<U> &Other) : Value(Other.Value), Tag(Other.Tag) {}
 
   template <class U>
-  Tagged(Tagged<U> &&Other) : Value(std::move(Other.Value)), Tag(Other.Tag) {}
+  Tagged(Tagged<U> &&Other)
+      : Value(std::move(Other.Value)), Tag(std::move(Other.Tag)) {}
 
   T Value;
   VFSTag Tag;
Index: clang-tools-extra/trunk/unittests/clangd/ClangdTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/ClangdTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/ClangdTests.cpp
@@ -386,13 +386,13 @@
   auto FooCpp = getVirtualTestFilePath("foo.cpp");
   const auto SourceContents = "int a;";
   FS->Files[FooCpp] = SourceContents;
-  FS->Tag = 123;
+  FS->Tag = "123";
 
   Server.addDocument(FooCpp, SourceContents);
   EXPECT_EQ(DiagConsumer->lastVFSTag(), FS->Tag);
   EXPECT_EQ(Server.codeComplete(FooCpp, Position{0, 0}).Tag, FS->Tag);
 
-  FS->Tag = 321;
+  FS->Tag = "321";
   Server.addDocument(FooCpp, SourceContents);
   EXPECT_EQ(DiagConsumer->lastVFSTag(), FS->Tag);
   EXPECT_EQ(Server.codeComplete(FooCpp, Position{0, 0}).Tag, FS->Tag);