[clangd] A comment for ClangdServer's constructor. NFC.

llvm-svn: 305299

clang-tools-extra/clangd/ClangdServer.h

@@ -136,6 +136,15 @@ private:
 /// diagnostics for tracked files).
 class ClangdServer {
 public:
+  /// Creates a new ClangdServer. If \p RunSynchronously is false, no worker
+  /// thread will be created and all requests will be completed synchronously on
+  /// the calling thread (this is mostly used for tests). If \p RunSynchronously
+  /// is true, a worker thread will be created to parse files in the background
+  /// and provide diagnostics results via DiagConsumer.onDiagnosticsReady
+  /// callback. File accesses for each instance of parsing will be conducted via
+  /// a vfs::FileSystem provided by \p FSProvider. Results of code
+  /// completion/diagnostics also include a tag, that \p FSProvider returns
+  /// along with the vfs::FileSystem.
   ClangdServer(GlobalCompilationDatabase &CDB,
                DiagnosticsConsumer &DiagConsumer,
                FileSystemProvider &FSProvider, bool RunSynchronously);