Index: unittests/clangd/SymbolCollectorTests.cpp
===================================================================
--- unittests/clangd/SymbolCollectorTests.cpp
+++ unittests/clangd/SymbolCollectorTests.cpp
@@ -7,8 +7,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "Annotations.h"
+#include "ClangdServer.h"
+#include "CodeComplete.h"
+#include "SyncAPI.h"
 #include "TestFS.h"
 #include "TestTU.h"
+#include "index/Index.h"
+#include "index/MemIndex.h"
 #include "index/SymbolCollector.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/FileSystemOptions.h"
@@ -50,6 +55,7 @@
 MATCHER_P(Snippet, S, "") {
   return (arg.Name + arg.CompletionSnippetSuffix).str() == S;
 }
+MATCHER_P(CompletionQName, Name, "") { return (arg.Scope + arg.Name) == Name; }
 MATCHER_P(QName, Name, "") { return (arg.Scope + arg.Name).str() == Name; }
 MATCHER_P(DeclURI, P, "") {
   return StringRef(arg.CanonicalDeclaration.FileURI) == P;
@@ -325,9 +331,6 @@
     // Namespace alias
     namespace baz = bar;
 
-    // FIXME: using declaration is not supported as the IndexAction will ignore
-    // implicit declarations (the implicit using shadow declaration) by default,
-    // and there is no way to customize this behavior at the moment.
     using bar::v2;
     } // namespace foo
   )";
@@ -354,6 +357,7 @@
                    AllOf(QName("foo::int32_t"), ForCodeCompletion(true)),
                    AllOf(QName("foo::v1"), ForCodeCompletion(true)),
                    AllOf(QName("foo::bar::v2"), ForCodeCompletion(true)),
+                   AllOf(QName("foo::v2"), ForCodeCompletion(true)),
                    AllOf(QName("foo::baz"), ForCodeCompletion(true))}));
 }
 
@@ -1118,6 +1122,48 @@
                   AllOf(QName("Public"), Not(ImplementationDetail()))));
 }
 
+TEST_F(SymbolCollectorTest, UsingDecl) {
+  auto completions = [](const Annotations &Test, SymbolSlab SS) {
+    class IgnoreDiagnostics : public DiagnosticsConsumer {
+      void onDiagnosticsReady(PathRef File,
+                              std::vector<Diag> Diagnostics) override {}
+    };
+
+    MockFSProvider FS;
+    MockCompilationDatabase CDB;
+    IgnoreDiagnostics DiagConsumer;
+    ClangdServer Server(CDB, FS, DiagConsumer, ClangdServer::optsForTest());
+    std::unique_ptr<SymbolIndex> OverrideIndex =
+        MemIndex::build(std::move(SS), {});
+    clangd::CodeCompleteOptions Opts;
+    Opts.Index = OverrideIndex.get();
+
+    auto File = testPath("foo.cpp");
+    runAddDocument(Server, File, Test.code());
+    auto CompletionList =
+        llvm::cantFail(runCodeComplete(Server, File, Test.point(), Opts));
+    return CompletionList;
+  };
+
+  const Annotations Header(R"(
+  void foo();
+  namespace std {
+    using ::foo;
+  }
+  void bar() {
+    (void)std::^foo;
+  })");
+  runSymbolCollector(Header.code(), /**/ "");
+  EXPECT_THAT(Symbols, Contains(QName("std::foo")));
+
+  const auto Results = completions(Header, std::move(Symbols));
+  EXPECT_THAT(
+      Results.Completions,
+      Contains(AllOf(
+          ReturnType(/*Currently using decls does not export target info*/ ""),
+          CompletionQName("std::foo"))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
Index: unittests/clangd/SymbolInfoTests.cpp
===================================================================
--- unittests/clangd/SymbolInfoTests.cpp
+++ unittests/clangd/SymbolInfoTests.cpp
@@ -167,7 +167,8 @@
         )cpp",
               {CreateExpectedSymbolDetails("foo", "", "c:@F@foo#"),
                CreateExpectedSymbolDetails("foo", "", "c:@F@foo#b#"),
-               CreateExpectedSymbolDetails("foo", "", "c:@F@foo#I#")}},
+               CreateExpectedSymbolDetails("foo", "", "c:@F@foo#I#"),
+               CreateExpectedSymbolDetails("foo", "bar::", "c:@N@bar@UD@foo")}},
           {
               R"cpp( // Multiple symbols returned - implicit conversion
           struct foo {};