carbon-lang/common/string_helpers.cpp

// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#include "common/string_helpers.h"

#include "common/check.h"
#include "llvm/ADT/StringExtras.h"

namespace Carbon {

// Carbon only takes uppercase hex input.
static auto FromHex(char c) -> std::optional<char> {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  if (c >= 'A' && c <= 'F') {
    return 10 + c - 'A';
  }
  return std::nullopt;
}

auto UnescapeStringLiteral(llvm::StringRef source)
    -> std::optional<std::string> {
  std::string ret;
  ret.reserve(source.size());
  size_t i = 0;
  while (i < source.size()) {
    char c = source[i];
    if (c == '\\') {
      ++i;
      if (i == source.size()) {
        return std::nullopt;
      }
      switch (source[i]) {
        case 'n':
          ret.push_back('\n');
          break;
        case 'r':
          ret.push_back('\r');
          break;
        case 't':
          ret.push_back('\t');
          break;
        case '0':
          if (i + 1 < source.size() && llvm::isDigit(source[i + 1])) {
            // \0[0-9] is reserved.
            return std::nullopt;
          }
          ret.push_back('\0');
          break;
        case '"':
          ret.push_back('"');
          break;
        case '\'':
          ret.push_back('\'');
          break;
        case '\\':
          ret.push_back('\\');
          break;
        case 'x': {
          i += 2;
          if (i >= source.size()) {
            return std::nullopt;
          }
          std::optional<char> c1 = FromHex(source[i - 1]);
          std::optional<char> c2 = FromHex(source[i]);
          if (c1 == std::nullopt || c2 == std::nullopt) {
            return std::nullopt;
          }
          ret.push_back(16 * *c1 + *c2);
          break;
        }
        case 'u':
          FATAL() << "\\u is not yet supported in string literals";
        default:
          // Unsupported.
          return std::nullopt;
      }
    } else {
      ret.push_back(c);
    }
    ++i;
  }
  return ret;
}

}  // namespace Carbon