[clangd] Also apply adjustArguments when returning fallback commands

[ilya-biryukov]

LGTM

clang-tools-extra/clangd/GlobalCompilationDatabase.cpp

 }
 
 tooling::CompileCommand OverlayCDB::getFallbackCommand(PathRef File) const {
   auto Cmd = Base ? Base->getFallbackCommand(File)
                   : GlobalCompilationDatabase::getFallbackCommand(File);
   std::lock_guard<std::mutex> Lock(Mutex);
   Cmd.CommandLine.insert(Cmd.CommandLine.end(), FallbackFlags.begin(),
                          FallbackFlags.end());
+  adjustArguments(Cmd, ResourceDir);
   return Cmd;
 }
 
 void OverlayCDB::setCompileCommand(
     PathRef File, llvm::Optional<tooling::CompileCommand> Cmd) {
   {
     std::unique_lock<std::mutex> Lock(Mutex);
     if (Cmd)

clang-tools-extra/clangd/unittests/GlobalCompilationDatabaseTests.cpp

 namespace clang {
 namespace clangd {
 namespace {
 using ::testing::AllOf;
 using ::testing::Contains;
 using ::testing::ElementsAre;
 using ::testing::EndsWith;
 using ::testing::Not;
+using ::testing::StartsWith;
 
 TEST(GlobalCompilationDatabaseTest, FallbackCommand) {
   DirectoryBasedGlobalCompilationDatabase DB(None);
   auto Cmd = DB.getFallbackCommand(testPath("foo/bar.cc"));
   EXPECT_EQ(Cmd.Directory, testPath("foo"));
   EXPECT_THAT(Cmd.CommandLine,
               ElementsAre(EndsWith("clang"), testPath("foo/bar.cc")));
   EXPECT_EQ(Cmd.Output, "");
TEST_F(OverlayCDBTest, GetCompileCommand) {
   CDB.setCompileCommand(testPath("missing.cc"), Override);
   EXPECT_THAT(CDB.getCompileCommand(testPath("missing.cc"))->CommandLine,
               Contains("-DA=3"));
 }
 
 TEST_F(OverlayCDBTest, GetFallbackCommand) {
   OverlayCDB CDB(Base.get(), {"-DA=4"});
   EXPECT_THAT(CDB.getFallbackCommand(testPath("bar.cc")).CommandLine,
-              ElementsAre("clang", "-DA=2", testPath("bar.cc"), "-DA=4"));
+              ElementsAre("clang", "-DA=2", testPath("bar.cc"), "-DA=4",
+                          "-fsyntax-only", StartsWith("-resource-dir")));
 }
 
 TEST_F(OverlayCDBTest, NoBase) {
   OverlayCDB CDB(nullptr, {"-DA=6"}, std::string(""));
   EXPECT_EQ(CDB.getCompileCommand(testPath("bar.cc")), None);
   auto Override = cmd(testPath("bar.cc"), "-DA=5");
   CDB.setCompileCommand(testPath("bar.cc"), Override);
   EXPECT_THAT(CDB.getCompileCommand(testPath("bar.cc"))->CommandLine,
               Contains("-DA=5"));
 
   EXPECT_THAT(CDB.getFallbackCommand(testPath("foo.cc")).CommandLine,
-              ElementsAre(EndsWith("clang"), testPath("foo.cc"), "-DA=6"));
+              ElementsAre(EndsWith("clang"), testPath("foo.cc"), "-DA=6",
+                          "-fsyntax-only"));
 }
 
 TEST_F(OverlayCDBTest, Watch) {
   OverlayCDB Inner(nullptr);
   OverlayCDB Outer(&Inner);
 
   std::vector<std::vector<std::string>> Changes;
   auto Sub = Outer.watch([&](const std::vector<std::string> &ChangedFiles) {