1//===--- Encoding.h - Format C++ code ---------------------------*- 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/// \file
10/// Contains functions for text encoding manipulation. Supports UTF-8,
11/// 8-bit encodings and escape sequences in C++ string literals.
12///
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_CLANG_LIB_FORMAT_ENCODING_H
16#define LLVM_CLANG_LIB_FORMAT_ENCODING_H
17
18#include "clang/Basic/LLVM.h"
19#include "llvm/ADT/StringRef.h"
20#include "llvm/Support/ConvertUTF.h"
21#include "llvm/Support/Unicode.h"
22
23namespace clang {
24namespace format {
25namespace encoding {
26
27enum Encoding {
28  Encoding_UTF8,
29  Encoding_Unknown // We treat all other encodings as 8-bit encodings.
30};
31
32/// Detects encoding of the Text. If the Text can be decoded using UTF-8,
33/// it is considered UTF8, otherwise we treat it as some 8-bit encoding.
34inline Encoding detectEncoding(StringRef Text) {
35  const llvm::UTF8 *Ptr = reinterpret_cast<const llvm::UTF8 *>(Text.begin());
36  const llvm::UTF8 *BufEnd = reinterpret_cast<const llvm::UTF8 *>(Text.end());
37  if (llvm::isLegalUTF8String(&Ptr, BufEnd))
38    return Encoding_UTF8;
39  return Encoding_Unknown;
40}
41
42/// Returns the number of columns required to display the \p Text on a
43/// generic Unicode-capable terminal. Text is assumed to use the specified
44/// \p Encoding.
45inline unsigned columnWidth(StringRef Text, Encoding Encoding) {
46  if (Encoding == Encoding_UTF8) {
47    int ContentWidth = llvm::sys::unicode::columnWidthUTF8(Text);
48    // FIXME: Figure out the correct way to handle this in the presence of both
49    // printable and unprintable multi-byte UTF-8 characters. Falling back to
50    // returning the number of bytes may cause problems, as columnWidth suddenly
51    // becomes non-additive.
52    if (ContentWidth >= 0)
53      return ContentWidth;
54  }
55  return Text.size();
56}
57
58/// Returns the number of columns required to display the \p Text,
59/// starting from the \p StartColumn on a terminal with the \p TabWidth. The
60/// text is assumed to use the specified \p Encoding.
61inline unsigned columnWidthWithTabs(StringRef Text, unsigned StartColumn,
62                                    unsigned TabWidth, Encoding Encoding) {
63  unsigned TotalWidth = 0;
64  StringRef Tail = Text;
65  for (;;) {
66    StringRef::size_type TabPos = Tail.find('\t');
67    if (TabPos == StringRef::npos)
68      return TotalWidth + columnWidth(Tail, Encoding);
69    TotalWidth += columnWidth(Tail.substr(0, TabPos), Encoding);
70    if (TabWidth)
71      TotalWidth += TabWidth - (TotalWidth + StartColumn) % TabWidth;
72    Tail = Tail.substr(TabPos + 1);
73  }
74}
75
76/// Gets the number of bytes in a sequence representing a single
77/// codepoint and starting with FirstChar in the specified Encoding.
78inline unsigned getCodePointNumBytes(char FirstChar, Encoding Encoding) {
79  switch (Encoding) {
80  case Encoding_UTF8:
81    return llvm::getNumBytesForUTF8(FirstChar);
82  default:
83    return 1;
84  }
85}
86
87inline bool isOctDigit(char c) { return '0' <= c && c <= '7'; }
88
89inline bool isHexDigit(char c) {
90  return ('0' <= c && c <= '9') || ('a' <= c && c <= 'f') ||
91         ('A' <= c && c <= 'F');
92}
93
94/// Gets the length of an escape sequence inside a C++ string literal.
95/// Text should span from the beginning of the escape sequence (starting with a
96/// backslash) to the end of the string literal.
97inline unsigned getEscapeSequenceLength(StringRef Text) {
98  assert(Text[0] == '\\');
99  if (Text.size() < 2)
100    return 1;
101
102  switch (Text[1]) {
103  case 'u':
104    return 6;
105  case 'U':
106    return 10;
107  case 'x': {
108    unsigned I = 2; // Point after '\x'.
109    while (I < Text.size() && isHexDigit(Text[I]))
110      ++I;
111    return I;
112  }
113  default:
114    if (isOctDigit(Text[1])) {
115      unsigned I = 1;
116      while (I < Text.size() && I < 4 && isOctDigit(Text[I]))
117        ++I;
118      return I;
119    }
120    return 1 + llvm::getNumBytesForUTF8(Text[1]);
121  }
122}
123
124} // namespace encoding
125} // namespace format
126} // namespace clang
127
128#endif
129