Index: clang/lib/IndexSerialization/FSUtil.h
===================================================================
--- /dev/null
+++ clang/lib/IndexSerialization/FSUtil.h
@@ -0,0 +1,67 @@
+//===--- FSUtil.h - File system utilities ---------------------------------===//
+//
+// 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_INDEX_FSUTIL_H
+#define LLVM_CLANG_INDEX_FSUTIL_H
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Errc.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace clang {
+namespace index {
+
+using namespace llvm;
+
+/// Creates a unique file with name according to the given \p TempPathModel,
+/// writes content of \p Buffer to the file and renames it to \p FinalPath.
+/// \returns false when the file was successfully created, true otherwise.
+inline bool atomicFileWrite(StringRef TempPathModel, StringRef FinalPath,
+                            const SmallString<512> &Buffer,
+                            std::string &Error) {
+  SmallString<128> GeneratedUniqPath;
+  int TempFD;
+  if (sys::fs::createUniqueFile(TempPathModel.str(), TempFD,
+                                GeneratedUniqPath)) {
+    raw_string_ostream Err(Error);
+    Err << "failed to create temporary file: " << TempPathModel;
+    return true;
+  }
+
+  raw_fd_ostream OS(TempFD, /*shouldClose=*/true);
+  OS.write(Buffer.data(), Buffer.size());
+  OS.close();
+  TempFD = -1;
+
+  if (OS.has_error()) {
+    raw_string_ostream Err(Error);
+    Err << "failed to write '" << GeneratedUniqPath
+        << "': " << OS.error().message();
+    OS.clear_error();
+    return true;
+  }
+
+  std::error_code EC = sys::fs::rename(/*from=*/GeneratedUniqPath.c_str(),
+                                       /*to=*/FinalPath.str().c_str());
+  if (EC) {
+    raw_string_ostream Err(Error);
+    Err << "failed to rename '" << GeneratedUniqPath << "' to '" << FinalPath
+        << "': " << EC.message();
+    return true;
+  }
+
+  return false;
+}
+
+} // end namespace index
+} // end namespace clang
+
+#endif