C++ StringRef::take_front方法代码示例

void Log::WriteHeader(llvm::raw_ostream &OS, llvm::StringRef file,
                      llvm::StringRef function) {
  Flags options = GetOptions();
  static uint32_t g_sequence_id = 0;
  // Add a sequence ID if requested
  if (options.Test(LLDB_LOG_OPTION_PREPEND_SEQUENCE))
    OS << ++g_sequence_id << " ";

  // Timestamp if requested
  if (options.Test(LLDB_LOG_OPTION_PREPEND_TIMESTAMP)) {
    auto now = std::chrono::duration<double>(
        std::chrono::system_clock::now().time_since_epoch());
    OS << llvm::formatv("{0:f9} ", now.count());
  }

  // Add the process and thread if requested
  if (options.Test(LLDB_LOG_OPTION_PREPEND_PROC_AND_THREAD))
    OS << llvm::formatv("[{0,0+4}/{1,0+4}] ", getpid(),
                        llvm::get_threadid());

  // Add the thread name if requested
  if (options.Test(LLDB_LOG_OPTION_PREPEND_THREAD_NAME)) {
    llvm::SmallString<32> thread_name;
    llvm::get_thread_name(thread_name);

    llvm::SmallString<12> format_str;
    llvm::raw_svector_ostream format_os(format_str);
    format_os << "{0,-" << llvm::alignTo<16>(thread_name.size()) << "} ";
    OS << llvm::formatv(format_str.c_str(), thread_name);
  }

  if (options.Test(LLDB_LOG_OPTION_BACKTRACE))
    llvm::sys::PrintStackTrace(OS);

  if (options.Test(LLDB_LOG_OPTION_PREPEND_FILE_FUNCTION) &&
      (!file.empty() || !function.empty())) {
    file = llvm::sys::path::filename(file).take_front(40);
    function = function.take_front(40);
    OS << llvm::formatv("{0,-60:60} ", (file + ":" + function).str());
  }
}

lldb::OptionValueSP
OptionValueProperties::GetSubValue(const ExecutionContext *exe_ctx,
  llvm::StringRef name, bool will_modify,
                                   Error &error) const {
  lldb::OptionValueSP value_sp;
  if (name.empty())
    return OptionValueSP();

  llvm::StringRef sub_name;
  ConstString key;
  size_t key_len = name.find_first_of(".[{");
  if (key_len != llvm::StringRef::npos) {
    key.SetString(name.take_front(key_len));
    sub_name = name.drop_front(key_len);
  } else
    key.SetString(name);

  value_sp = GetValueForKey(exe_ctx, key, will_modify);
  if (sub_name.empty() || !value_sp)
    return value_sp;

  switch (sub_name[0]) {
  case '.': {
    lldb::OptionValueSP return_val_sp;
    return_val_sp =
        value_sp->GetSubValue(exe_ctx, sub_name.drop_front(), will_modify, error);
    if (!return_val_sp) {
      if (Properties::IsSettingExperimental(sub_name.drop_front())) {
        size_t experimental_len =
            strlen(Properties::GetExperimentalSettingsName());
        if (sub_name[experimental_len + 1] == '.')
          return_val_sp = value_sp->GetSubValue(
              exe_ctx, sub_name.drop_front(experimental_len + 2), will_modify, error);
        // It isn't an error if an experimental setting is not present.
        if (!return_val_sp)
          error.Clear();
      }
    }
    return return_val_sp;
  }
  case '{':
    // Predicate matching for predicates like
    // "<setting-name>{<predicate>}"
    // strings are parsed by the current OptionValueProperties subclass
    // to mean whatever they want to. For instance a subclass of
    // OptionValueProperties for a lldb_private::Target might implement:
    // "target.run-args{arch==i386}"   -- only set run args if the arch is
    // i386
    // "target.run-args{path=/tmp/a/b/c/a.out}" -- only set run args if the
    // path matches
    // "target.run-args{basename==test&&arch==x86_64}" -- only set run args
    // if executable basename is "test" and arch is "x86_64"
    if (sub_name[1]) {
      llvm::StringRef predicate_start = sub_name.drop_front();
      size_t pos = predicate_start.find_first_of('}');
      if (pos != llvm::StringRef::npos) {
        auto predicate = predicate_start.take_front(pos);
        auto rest = predicate_start.drop_front(pos);
        if (PredicateMatches(exe_ctx, predicate)) {
          if (!rest.empty()) {
            // Still more subvalue string to evaluate
            return value_sp->GetSubValue(exe_ctx, rest,
                                          will_modify, error);
          } else {
            // We have a match!
            break;
          }
        }
      }
    }
    // Predicate didn't match or wasn't correctly formed
    value_sp.reset();
    break;

  case '[':
    // Array or dictionary access for subvalues like:
    // "[12]"       -- access 12th array element
    // "['hello']"  -- dictionary access of key named hello
    return value_sp->GetSubValue(exe_ctx, sub_name, will_modify, error);

  default:
    value_sp.reset();
    break;
  }
  return value_sp;
}

static void demangle(llvm::raw_ostream &os, llvm::StringRef name,
                     swift::Demangle::Context &DCtx,
                     const swift::Demangle::DemangleOptions &options) {
  bool hadLeadingUnderscore = false;
  if (name.startswith("__")) {
    hadLeadingUnderscore = true;
    name = name.substr(1);
  }
  swift::Demangle::NodePointer pointer = DCtx.demangleSymbolAsNode(name);
  if (ExpandMode || TreeOnly) {
    llvm::outs() << "Demangling for " << name << '\n';
    llvm::outs() << getNodeTreeAsString(pointer);
  }
  if (RemangleMode) {
    std::string remangled;
    if (!pointer || !(name.startswith(MANGLING_PREFIX_STR) ||
                      name.startswith("_S"))) {
      // Just reprint the original mangled name if it didn't demangle or is in
      // the old mangling scheme.
      // This makes it easier to share the same database between the
      // mangling and demangling tests.
      remangled = name;
    } else {
      remangled = swift::Demangle::mangleNode(pointer);
      unsigned prefixLen = swift::Demangle::getManglingPrefixLength(remangled);
      assert(prefixLen > 0);
      // Replace the prefix if we remangled with a different prefix.
      if (!name.startswith(remangled.substr(0, prefixLen))) {
        unsigned namePrefixLen =
          swift::Demangle::getManglingPrefixLength(name);
        assert(namePrefixLen > 0);
        remangled = name.take_front(namePrefixLen).str() +
                      remangled.substr(prefixLen);
      }
      if (name != remangled) {
        llvm::errs() << "\nError: re-mangled name \n  " << remangled
                     << "\ndoes not match original name\n  " << name << '\n';
        exit(1);
      }
    }
    if (hadLeadingUnderscore) llvm::outs() << '_';
    llvm::outs() << remangled;
    return;
  } else if (RemangleRtMode) {
    std::string remangled = name;
    if (pointer) {
      remangled = swift::Demangle::mangleNodeOld(pointer);
    }
    llvm::outs() << remangled;
  }
  if (!TreeOnly) {
    if (RemangleNew) {
      if (!pointer) {
        llvm::errs() << "Can't de-mangle " << name << '\n';
        exit(1);
      }
      std::string remangled = swift::Demangle::mangleNode(pointer);
      llvm::outs() << remangled;
      return;
    }
    std::string string = swift::Demangle::nodeToString(pointer, options);
    if (!CompactMode)
      llvm::outs() << name << " ---> ";

    if (Classify) {
      std::string Classifications;
      if (!swift::Demangle::isSwiftSymbol(name))
        Classifications += 'N';
      if (DCtx.isThunkSymbol(name)) {
        if (!Classifications.empty())
          Classifications += ',';
        Classifications += "T:";
        Classifications += DCtx.getThunkTarget(name);
      } else {
        assert(DCtx.getThunkTarget(name).empty());
      }
      if (pointer && !DCtx.hasSwiftCallingConvention(name)) {
        if (!Classifications.empty())
          Classifications += ',';
        Classifications += 'C';
      }
      if (!Classifications.empty())
        llvm::outs() << '{' << Classifications << "} ";
    }
    llvm::outs() << (string.empty() ? name : llvm::StringRef(string));
  }
  DCtx.clear();
}