--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/clang-tools-extra/clangd/ASTSignals.h	Tue Jun 15 19:15:29 2021 +0900
@@ -0,0 +1,39 @@
+//===--- ASTSignals.h --------------------------------------------*- C++-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_ASTSIGNALS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_ASTSIGNALS_H
+
+#include "ParsedAST.h"
+#include "index/SymbolID.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/StringMap.h"
+
+namespace clang {
+namespace clangd {
+
+/// Signals derived from a valid AST of a file.
+/// Provides information that can only be extracted from the AST to actions that
+/// can't access an AST. The signals are computed and updated asynchronously by
+/// the ASTWorker and thus they are always stale and also can be absent.
+/// Example usage: Information about the declarations used in a file affects
+/// code-completion ranking in that file.
+struct ASTSignals {
+  /// Number of occurrences of each symbol present in the file.
+  llvm::DenseMap<SymbolID, unsigned> ReferencedSymbols;
+  /// Namespaces whose symbols are used in the file, and the number of such
+  /// distinct symbols.
+  llvm::StringMap<unsigned> RelatedNamespaces;
+
+  static ASTSignals derive(const ParsedAST &AST);
+};
+
+} // namespace clangd
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_ASTSIGNALS_H