[clangd] Switch to Dex by default for the static index

[kbobyrev]

Summary

Dex is now mature enough to be used as the default static index. This patch performs the switch but introduces a hidden flag to allow users fallback to Mem in case something happens.

[kbobyrev]

Run clang-format.

[ioeric]

clang-tools-extra/clangd/tool/ClangdMain.cpp

32

I think we should stick to the same option and just flip the default. Introducing yet another option (that is going to be removed) could be confusing.

33

Also add FIXME indicating that the option will be removed soon.

[ioeric]

clang-tools-extra/clangd/tool/ClangdMain.cpp

32

Maybe: FIXME: remove this option when Dex is stable enough.

clang-tools-extra/clangd/tool/ClangdMain.cpp

 #include <iostream>
 #include <memory>
 #include <string>
 #include <thread>
 
 using namespace clang;
 using namespace clang::clangd;
 
+// FIXME(kbobyrev): This option should be removed as Dex is now the default
+// static index.
 static llvm::cl::opt<bool>
     UseDex("use-dex-index",
            llvm::cl::desc("Use experimental Dex static index."),
-           llvm::cl::init(false), llvm::cl::Hidden);
+           llvm::cl::init(true), llvm::cl::Hidden);
 
 namespace {
 
 enum class PCHStorageFlag { Disk, Memory };
 
 // Build an in-memory static index for global symbols from a YAML-format file.
 // The size of global symbols should be relatively small, so that all symbols
 // can be managed in memory.