Index: clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.h
===================================================================
--- clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.h
+++ clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.h
@@ -52,6 +52,7 @@
 public:
   DirectoryBasedGlobalCompilationDatabase(
       llvm::Optional<Path> CompileCommandsDir);
+  ~DirectoryBasedGlobalCompilationDatabase() override;
 
   /// Scans File's parents looking for compilation databases.
   /// Any extra flags will be added.
Index: clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
+++ clang-tools-extra/trunk/clangd/GlobalCompilationDatabase.cpp
@@ -18,9 +18,15 @@
 
 tooling::CompileCommand
 GlobalCompilationDatabase::getFallbackCommand(PathRef File) const {
+  std::vector<std::string> Argv = {"clang"};
+  // Clang treats .h files as C by default, resulting in unhelpful diagnostics.
+  // Parsing as Objective C++ is friendly to more cases.
+  if (llvm::sys::path::extension(File) == ".h")
+    Argv.push_back("-xobjective-c++-header");
+  Argv.push_back(File);
   return tooling::CompileCommand(llvm::sys::path::parent_path(File),
                                  llvm::sys::path::filename(File),
-                                 {"clang", File.str()},
+                                 std::move(Argv),
                                  /*Output=*/"");
 }
 
@@ -29,6 +35,9 @@
         llvm::Optional<Path> CompileCommandsDir)
     : CompileCommandsDir(std::move(CompileCommandsDir)) {}
 
+DirectoryBasedGlobalCompilationDatabase::
+    ~DirectoryBasedGlobalCompilationDatabase() = default;
+
 llvm::Optional<tooling::CompileCommand>
 DirectoryBasedGlobalCompilationDatabase::getCompileCommand(PathRef File) const {
   if (auto CDB = getCDBForFile(File)) {
Index: clang-tools-extra/trunk/unittests/clangd/CMakeLists.txt
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/CMakeLists.txt
+++ clang-tools-extra/trunk/unittests/clangd/CMakeLists.txt
@@ -18,6 +18,7 @@
   DraftStoreTests.cpp
   FileIndexTests.cpp
   FuzzyMatchTests.cpp
+  GlobalCompilationDatabaseTests.cpp
   HeadersTests.cpp
   IndexTests.cpp
   JSONExprTests.cpp
Index: clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/GlobalCompilationDatabaseTests.cpp
@@ -0,0 +1,37 @@
+//===-- GlobalCompilationDatabaseTests.cpp ----------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "GlobalCompilationDatabase.h"
+
+#include "TestFS.h"
+#include "llvm/ADT/StringExtras.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+namespace clang {
+namespace clangd {
+namespace {
+using ::testing::ElementsAre;
+
+TEST(GlobalCompilationDatabaseTest, FallbackCommand) {
+  DirectoryBasedGlobalCompilationDatabase DB(llvm::None);
+  auto Cmd = DB.getFallbackCommand(testPath("foo/bar.cc"));
+  EXPECT_EQ(Cmd.Directory, testPath("foo"));
+  EXPECT_THAT(Cmd.CommandLine, ElementsAre("clang", testPath("foo/bar.cc")));
+  EXPECT_EQ(Cmd.Output, "");
+
+  // .h files have unknown language, so they are parsed liberally as obj-c++.
+  Cmd = DB.getFallbackCommand(testPath("foo/bar.h"));
+  EXPECT_THAT(Cmd.CommandLine, ElementsAre("clang", "-xobjective-c++-header",
+                                           testPath("foo/bar.h")));
+}
+
+} // namespace
+} // namespace clangd
+} // namespace clang
Index: clang-tools-extra/trunk/unittests/clangd/TestFS.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/TestFS.cpp
+++ clang-tools-extra/trunk/unittests/clangd/TestFS.cpp
@@ -55,8 +55,10 @@
 std::string testPath(PathRef File) {
   assert(sys::path::is_relative(File) && "FileName should be relative");
 
+  SmallString<32> NativeFile = File;
+  sys::path::native(NativeFile);
   SmallString<32> Path;
-  sys::path::append(Path, testRoot(), File);
+  sys::path::append(Path, testRoot(), NativeFile);
   return Path.str();
 }