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diff --git a/clang-r353983e/include/clang/Lex/HeaderMap.h b/clang-r353983e/include/clang/Lex/HeaderMap.h
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+//===--- HeaderMap.h - A file that acts like dir of symlinks ----*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the HeaderMap interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_LEX_HEADERMAP_H
+#define LLVM_CLANG_LEX_HEADERMAP_H
+
+#include "clang/Basic/LLVM.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include <memory>
+
+namespace clang {
+
+class FileEntry;
+class FileManager;
+struct HMapBucket;
+struct HMapHeader;
+
+/// Implementation for \a HeaderMap that doesn't depend on \a FileManager.
+class HeaderMapImpl {
+  std::unique_ptr<const llvm::MemoryBuffer> FileBuffer;
+  bool NeedsBSwap;
+
+public:
+  HeaderMapImpl(std::unique_ptr<const llvm::MemoryBuffer> File, bool NeedsBSwap)
+      : FileBuffer(std::move(File)), NeedsBSwap(NeedsBSwap) {}
+
+  // Check for a valid header and extract the byte swap.
+  static bool checkHeader(const llvm::MemoryBuffer &File, bool &NeedsByteSwap);
+
+  /// If the specified relative filename is located in this HeaderMap return
+  /// the filename it is mapped to, otherwise return an empty StringRef.
+  StringRef lookupFilename(StringRef Filename,
+                           SmallVectorImpl<char> &DestPath) const;
+
+  /// Return the filename of the headermap.
+  StringRef getFileName() const;
+
+  /// Print the contents of this headermap to stderr.
+  void dump() const;
+
+private:
+  unsigned getEndianAdjustedWord(unsigned X) const;
+  const HMapHeader &getHeader() const;
+  HMapBucket getBucket(unsigned BucketNo) const;
+
+  /// Look up the specified string in the string table.  If the string index is
+  /// not valid, return None.
+  Optional<StringRef> getString(unsigned StrTabIdx) const;
+};
+
+/// This class represents an Apple concept known as a 'header map'.  To the
+/// \#include file resolution process, it basically acts like a directory of
+/// symlinks to files.  Its advantages are that it is dense and more efficient
+/// to create and process than a directory of symlinks.
+class HeaderMap : private HeaderMapImpl {
+  HeaderMap(std::unique_ptr<const llvm::MemoryBuffer> File, bool BSwap)
+      : HeaderMapImpl(std::move(File), BSwap) {}
+
+public:
+  /// This attempts to load the specified file as a header map.  If it doesn't
+  /// look like a HeaderMap, it gives up and returns null.
+  static std::unique_ptr<HeaderMap> Create(const FileEntry *FE,
+                                           FileManager &FM);
+
+  /// Check to see if the specified relative filename is located in this
+  /// HeaderMap.  If so, open it and return its FileEntry.  If RawPath is not
+  /// NULL and the file is found, RawPath will be set to the raw path at which
+  /// the file was found in the file system. For example, for a search path
+  /// ".." and a filename "../file.h" this would be "../../file.h".
+  const FileEntry *LookupFile(StringRef Filename, FileManager &FM) const;
+
+  using HeaderMapImpl::lookupFilename;
+  using HeaderMapImpl::getFileName;
+  using HeaderMapImpl::dump;
+};
+
+} // end namespace clang.
+
+#endif