Index: clangd/CodeComplete.cpp
===================================================================
--- clangd/CodeComplete.cpp
+++ clangd/CodeComplete.cpp
@@ -243,6 +243,8 @@
                        const IncludeInserter &Includes,
                        llvm::StringRef SemaDocComment) const {
     assert(bool(SemaResult) == bool(SemaCCS));
+    assert(bool(SemaResult) || bool(IndexResult));
+
     CompletionItem I;
     bool InsertingInclude = false; // Whether a new #include will be added.
     if (SemaResult) {
@@ -252,8 +254,14 @@
       I.filterText = getFilterText(*SemaCCS);
       I.documentation = formatDocumentation(*SemaCCS, SemaDocComment);
       I.detail = getDetail(*SemaCCS);
+      if (SemaResult->Kind == CodeCompletionResult::RK_Declaration)
+        if (const auto *D = SemaResult->getDeclaration())
+          if (const auto *ND = llvm::dyn_cast<NamedDecl>(D))
+            I.QualifiedName = ND->getQualifiedNameAsString();
     }
     if (IndexResult) {
+      if (I.QualifiedName.empty())
+        I.QualifiedName = (IndexResult->Scope + IndexResult->Name).str();
       if (I.kind == CompletionItemKind::Missing)
         I.kind = toCompletionItemKind(IndexResult->SymInfo.Kind);
       // FIXME: reintroduce a way to show the index source for debugging.
Index: clangd/Protocol.h
===================================================================
--- clangd/Protocol.h
+++ clangd/Protocol.h
@@ -734,6 +734,13 @@
   //
   // data?: any - A data entry field that is preserved on a completion item
   //              between a completion and a completion resolve request.
+
+  // C++ extension that is only expected to be used by users of ClangdServer's
+  // C++ API. Not serialized from/to json.
+  /// Qualified name of the symbol this item corresponds to. Empty if the item
+  /// has no corresponding symbol (e.g. keyword).
+  /// FIXME: find a more precise way to identify a completion item.
+  std::string QualifiedSymbolName;
 };
 json::Expr toJSON(const CompletionItem &);
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const CompletionItem &);
Index: unittests/clangd/CodeCompleteTests.cpp
===================================================================
--- unittests/clangd/CodeCompleteTests.cpp
+++ unittests/clangd/CodeCompleteTests.cpp
@@ -44,6 +44,7 @@
 
 // GMock helpers for matching completion items.
 MATCHER_P(Named, Name, "") { return arg.insertText == Name; }
+MATCHER_P(QName, Name, "") { return arg.QualifiedName == Name; }
 MATCHER_P(Labeled, Label, "") {
   std::string Indented;
   if (!StringRef(Label).startswith(
@@ -1251,6 +1252,18 @@
       Failed());
 }
 
+TEST(CompletionTest, QualifiedNames) {
+  auto Results = completions(
+      R"cpp(
+          namespace ns { int local; void both(); }
+          void f() { ::ns::^ }
+      )cpp",
+      {func("ns::both"), cls("ns::Index")});
+  // We get results from both index and sema, with no duplicates.
+  EXPECT_THAT(Results.items,
+              UnorderedElementsAre(QName("ns::local"), QName("ns::Index"),
+                                   QName("ns::both")));
+}
 
 } // namespace
 } // namespace clangd