Index: unittests/clangd/CodeCompleteTests.cpp
===================================================================
--- unittests/clangd/CodeCompleteTests.cpp
+++ unittests/clangd/CodeCompleteTests.cpp
@@ -17,6 +17,7 @@
 #include "SyncAPI.h"
 #include "TestFS.h"
 #include "TestIndex.h"
+#include "TestTU.h"
 #include "index/MemIndex.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "llvm/Support/Error.h"
@@ -2314,6 +2315,26 @@
   EXPECT_THAT(R.Completions, ElementsAre(Named("loopVar")));
 }
 
+TEST(CompletionTest, UsingDecl) {
+  const char *Header(R"cpp(
+    void foo(int);
+    namespace std {
+      using ::foo;
+    })cpp");
+  const char *Source(R"cpp(
+    void bar() {
+      std::^;
+    })cpp");
+  auto Index = TestTU::withHeaderCode(Header).index();
+  clangd::CodeCompleteOptions Opts;
+  Opts.Index = Index.get();
+  Opts.AllScopes = true;
+  auto R = completions(Source, {}, Opts);
+  EXPECT_THAT(R.Completions,
+              ElementsAre(AllOf(Scope("std::"), Named("foo"),
+                                Kind(CompletionItemKind::Reference))));
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang
Index: unittests/clangd/FindSymbolsTests.cpp
===================================================================
--- unittests/clangd/FindSymbolsTests.cpp
+++ unittests/clangd/FindSymbolsTests.cpp
@@ -368,9 +368,6 @@
       // 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
     )");
@@ -415,7 +412,7 @@
                                           Children()))),
                      AllOf(WithName("baz"), WithKind(SymbolKind::Namespace),
                            Children()),
-                     AllOf(WithName("v2"), WithKind(SymbolKind::Variable))))}));
+                     AllOf(WithName("v2"), WithKind(SymbolKind::Namespace))))}));
 }
 
 TEST_F(DocumentSymbolsTest, DeclarationDefinition) {
Index: unittests/clangd/SymbolCollectorTests.cpp
===================================================================
--- unittests/clangd/SymbolCollectorTests.cpp
+++ unittests/clangd/SymbolCollectorTests.cpp
@@ -331,9 +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
   )";
@@ -360,6 +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))}));
 }
 
@@ -1149,6 +1147,16 @@
                   AllOf(QName("Public"), Not(ImplementationDetail()))));
 }
 
+TEST_F(SymbolCollectorTest, UsingDecl) {
+  const char *Header = R"(
+  void foo();
+  namespace std {
+    using ::foo;
+  })";
+  runSymbolCollector(Header, /**/ "");
+  EXPECT_THAT(Symbols, Contains(QName("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 {};