1 //===--- HeaderMap.h - A file that acts like dir of symlinks ----*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the HeaderMap interface.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CLANG_LEX_HEADERMAP_H
14 #define LLVM_CLANG_LEX_HEADERMAP_H
15 
16 #include "clang/Basic/FileManager.h"
17 #include "clang/Basic/LLVM.h"
18 #include "clang/Lex/HeaderMapTypes.h"
19 #include "llvm/ADT/StringMap.h"
20 #include "llvm/Support/Compiler.h"
21 #include "llvm/Support/MemoryBuffer.h"
22 #include <memory>
23 #include <optional>
24 
25 namespace clang {
26 
27 struct HMapBucket;
28 struct HMapHeader;
29 
30 /// Implementation for \a HeaderMap that doesn't depend on \a FileManager.
31 class HeaderMapImpl {
32   std::unique_ptr<const llvm::MemoryBuffer> FileBuffer;
33   bool NeedsBSwap;
34   mutable llvm::StringMap<StringRef> ReverseMap;
35 
36 public:
37   HeaderMapImpl(std::unique_ptr<const llvm::MemoryBuffer> File, bool NeedsBSwap)
38       : FileBuffer(std::move(File)), NeedsBSwap(NeedsBSwap) {}
39 
40   // Check for a valid header and extract the byte swap.
41   static bool checkHeader(const llvm::MemoryBuffer &File, bool &NeedsByteSwap);
42 
43   // Make a call for every Key in the map.
44   template <typename Func> void forEachKey(Func Callback) const {
45     const HMapHeader &Hdr = getHeader();
46     unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
47 
48     for (unsigned Bucket = 0; Bucket < NumBuckets; ++Bucket) {
49       HMapBucket B = getBucket(Bucket);
50       if (B.Key != HMAP_EmptyBucketKey)
51         if (std::optional<StringRef> Key = getString(B.Key))
52           Callback(*Key);
53     }
54   }
55 
56   /// If the specified relative filename is located in this HeaderMap return
57   /// the filename it is mapped to, otherwise return an empty StringRef.
58   StringRef lookupFilename(StringRef Filename,
59                            SmallVectorImpl<char> &DestPath) const;
60 
61   /// Return the filename of the headermap.
62   StringRef getFileName() const;
63 
64   /// Print the contents of this headermap to stderr.
65   void dump() const;
66 
67   /// Return key for specifed path.
68   StringRef reverseLookupFilename(StringRef DestPath) const;
69 
70 private:
71   unsigned getEndianAdjustedWord(unsigned X) const;
72   const HMapHeader &getHeader() const;
73   HMapBucket getBucket(unsigned BucketNo) const;
74 
75   /// Look up the specified string in the string table.  If the string index is
76   /// not valid, return std::nullopt.
77   std::optional<StringRef> getString(unsigned StrTabIdx) const;
78 };
79 
80 /// This class represents an Apple concept known as a 'header map'.  To the
81 /// \#include file resolution process, it basically acts like a directory of
82 /// symlinks to files.  Its advantages are that it is dense and more efficient
83 /// to create and process than a directory of symlinks.
84 class HeaderMap : private HeaderMapImpl {
85   HeaderMap(std::unique_ptr<const llvm::MemoryBuffer> File, bool BSwap)
86       : HeaderMapImpl(std::move(File), BSwap) {}
87 
88 public:
89   /// This attempts to load the specified file as a header map.  If it doesn't
90   /// look like a HeaderMap, it gives up and returns null.
91   static std::unique_ptr<HeaderMap> Create(const FileEntry *FE,
92                                            FileManager &FM);
93 
94   using HeaderMapImpl::dump;
95   using HeaderMapImpl::forEachKey;
96   using HeaderMapImpl::getFileName;
97   using HeaderMapImpl::lookupFilename;
98   using HeaderMapImpl::reverseLookupFilename;
99 };
100 
101 } // end namespace clang.
102 
103 #endif
104