[clangd] Log directory when a CDB is loaded

[kadircet]

Summary

Fixes https://github.com/clangd/clangd/issues/268

[sammccall]

clang-tools-extra/clangd/GlobalCompilationDatabase.cpp

122

consider "Loaded compile commands..." or "Loading compile commands..." or "Loaded compilation database...".
People who are only dimly aware of the existence of compile_commands.json need a bit more context here.

122

this is significant and rare, probably OK to log rather than vlog

[merge_guards_bot]

Unit tests: pass. 62284 tests passed, 0 failed and 831 were skipped.

clang-tidy: pass.

clang-format: pass.

Build artifacts: diff.json, clang-tidy.txt, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

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[kadircet]

• Address comments

clang-tools-extra/clangd/GlobalCompilationDatabase.cpp

 DirectoryBasedGlobalCompilationDatabase::CachedCDB &
 DirectoryBasedGlobalCompilationDatabase::getCDBInDirLocked(PathRef Dir) const {
   // FIXME(ibiryukov): Invalidate cached compilation databases on changes
   // FIXME(sammccall): this function hot, avoid copying key when hitting cache.
   auto Key = maybeCaseFoldPath(Dir);
   auto R = CompilationDatabases.try_emplace(Key);
   if (R.second) { // Cache miss, try to load CDB.
     CachedCDB &Entry = R.first->second;
-    std::string Error = "";
+    std::string Error;
     Entry.CDB = tooling::CompilationDatabase::loadFromDirectory(Dir, Error);
     Entry.Path = std::string(Dir);
+    if (Entry.CDB)
+      log("Loaded compilation database from {0}", Dir);
   }
   return R.first->second;
 }
 
 llvm::Optional<DirectoryBasedGlobalCompilationDatabase::CDBLookupResult>
 DirectoryBasedGlobalCompilationDatabase::lookupCDB(
     CDBLookupRequest Request) const {
   assert(llvm::sys::path::is_absolute(Request.FileName) &&