[clangd] Enable standard library index by default.

[kadircet]

thanks, LG but seems to be failing on windows :/

[sammccall]

tickle premerge test

[sammccall]

In D133968#3794850, @kadircet wrote:

thanks, LG but seems to be failing on windows :/

This seemed very plausible but then none of the actual tests hit this codepath, and everything passes on rerun :-\

clang-tools-extra/clangd/Config.h

struct ExternalIndexSpec {
     /// forward-slashes.
     std::string MountPoint;
   };
   /// Controls index behavior.
   struct {
     /// Whether this TU should be background-indexed.
     BackgroundPolicy Background = BackgroundPolicy::Build;
     ExternalIndexSpec External;
-    bool StandardLibrary = false;
+    bool StandardLibrary = true;
   } Index;
 
   enum UnusedIncludesPolicy { Strict, None };
   /// Controls warnings and errors when parsing code.
   struct {
     bool SuppressAll = false;
     llvm::StringSet<> Suppress;
 

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

opt<Path> IndexFile{
     Hidden,
 };
 
 opt<bool> Test{
     "lit-test",
     cat(Misc),
     desc("Abbreviation for -input-style=delimited -pretty -sync "
          "-enable-test-scheme -enable-config=0 -log=verbose -crash-pragmas. "
+         "Also sets config options: Index.StandardLibrary=false. "
          "Intended to simplify lit tests"),
     init(false),
     Hidden,
 };
 
 opt<bool> CrashPragmas{
     "crash-pragmas",
     cat(Misc),
Frag = [=](const config::Params &, Config &C) {
       if (CDBSearch)
         C.CompileFlags.CDBSearch = *CDBSearch;
       if (IndexSpec)
         C.Index.External = *IndexSpec;
       if (BGPolicy)
         C.Index.Background = *BGPolicy;
       if (AllScopesCompletion.getNumOccurrences())
         C.Completion.AllScopes = AllScopesCompletion;
+
+      if (Test)
+        C.Index.StandardLibrary = false;
       return true;
     };
   }
 };
 } // namespace
 } // namespace clangd
 } // namespace clang