abseil-cpp/absl/strings/internal/str_format/parser.cc

// Copyright 2020 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#include "absl/strings/internal/str_format/parser.h"

#include <assert.h>
#include <string.h>
#include <wchar.h>
#include <cctype>
#include <cstdint>

#include <algorithm>
#include <initializer_list>
#include <limits>
#include <ostream>
#include <string>
#include <unordered_set>

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace str_format_internal {

using CC = FormatConversionCharInternal;
using LM = LengthMod;

ABSL_CONST_INIT const ConvTag kTags[256] = {
    {},    {},    {},    {},    {},    {},    {},    {},     // 00-07
    {},    {},    {},    {},    {},    {},    {},    {},     // 08-0f
    {},    {},    {},    {},    {},    {},    {},    {},     // 10-17
    {},    {},    {},    {},    {},    {},    {},    {},     // 18-1f
    {},    {},    {},    {},    {},    {},    {},    {},     // 20-27
    {},    {},    {},    {},    {},    {},    {},    {},     // 28-2f
    {},    {},    {},    {},    {},    {},    {},    {},     // 30-37
    {},    {},    {},    {},    {},    {},    {},    {},     // 38-3f
    {},    CC::A, {},    {},    {},    CC::E, CC::F, CC::G,  // @ABCDEFG
    {},    {},    {},    {},    LM::L, {},    {},    {},     // HIJKLMNO
    {},    {},    {},    {},    {},    {},    {},    {},     // PQRSTUVW
    CC::X, {},    {},    {},    {},    {},    {},    {},     // XYZ[\]^_
    {},    CC::a, {},    CC::c, CC::d, CC::e, CC::f, CC::g,  // `abcdefg
    LM::h, CC::i, LM::j, {},    LM::l, {},    CC::n, CC::o,  // hijklmno
    CC::p, LM::q, {},    CC::s, LM::t, CC::u, {},    {},     // pqrstuvw
    CC::x, {},    LM::z, {},    {},    {},    {},    {},     // xyz{|}!
    {},    {},    {},    {},    {},    {},    {},    {},     // 80-87
    {},    {},    {},    {},    {},    {},    {},    {},     // 88-8f
    {},    {},    {},    {},    {},    {},    {},    {},     // 90-97
    {},    {},    {},    {},    {},    {},    {},    {},     // 98-9f
    {},    {},    {},    {},    {},    {},    {},    {},     // a0-a7
    {},    {},    {},    {},    {},    {},    {},    {},     // a8-af
    {},    {},    {},    {},    {},    {},    {},    {},     // b0-b7
    {},    {},    {},    {},    {},    {},    {},    {},     // b8-bf
    {},    {},    {},    {},    {},    {},    {},    {},     // c0-c7
    {},    {},    {},    {},    {},    {},    {},    {},     // c8-cf
    {},    {},    {},    {},    {},    {},    {},    {},     // d0-d7
    {},    {},    {},    {},    {},    {},    {},    {},     // d8-df
    {},    {},    {},    {},    {},    {},    {},    {},     // e0-e7
    {},    {},    {},    {},    {},    {},    {},    {},     // e8-ef
    {},    {},    {},    {},    {},    {},    {},    {},     // f0-f7
    {},    {},    {},    {},    {},    {},    {},    {},     // f8-ff
};

namespace {

bool CheckFastPathSetting(const UnboundConversion& conv) {
  bool should_be_basic = !conv.flags.left &&      //
                         !conv.flags.show_pos &&  //
                         !conv.flags.sign_col &&  //
                         !conv.flags.alt &&       //
                         !conv.flags.zero &&      //
                         (conv.width.value() == -1) &&
                         (conv.precision.value() == -1);
  if (should_be_basic != conv.flags.basic) {
    fprintf(stderr,
            "basic=%d left=%d show_pos=%d sign_col=%d alt=%d zero=%d "
            "width=%d precision=%d\n",
            conv.flags.basic, conv.flags.left, conv.flags.show_pos,
            conv.flags.sign_col, conv.flags.alt, conv.flags.zero,
            conv.width.value(), conv.precision.value());
  }
  return should_be_basic == conv.flags.basic;
}

template <bool is_positional>
const char *ConsumeConversion(const char *pos, const char *const end,
                              UnboundConversion *conv, int *next_arg) {
  const char* const original_pos = pos;
  char c;
  // Read the next char into `c` and update `pos`. Returns false if there are
  // no more chars to read.
#define ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR()          \
  do {                                                  \
    if (ABSL_PREDICT_FALSE(pos == end)) return nullptr; \
    c = *pos++;                                         \
  } while (0)

  const auto parse_digits = [&] {
    int digits = c - '0';
    // We do not want to overflow `digits` so we consume at most digits10
    // digits. If there are more digits the parsing will fail later on when the
    // digit doesn't match the expected characters.
    int num_digits = std::numeric_limits<int>::digits10;
    for (;;) {
      if (ABSL_PREDICT_FALSE(pos == end)) break;
      c = *pos++;
      if (!std::isdigit(c)) break;
      --num_digits;
      if (ABSL_PREDICT_FALSE(!num_digits)) break;
      digits = 10 * digits + c - '0';
    }
    return digits;
  };

  if (is_positional) {
    ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
    if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
    conv->arg_position = parse_digits();
    assert(conv->arg_position > 0);
    if (ABSL_PREDICT_FALSE(c != '$')) return nullptr;
  }

  ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();

  // We should start with the basic flag on.
  assert(conv->flags.basic);

  // Any non alpha character makes this conversion not basic.
  // This includes flags (-+ #0), width (1-9, *) or precision (.).
  // All conversion characters and length modifiers are alpha characters.
  if (c < 'A') {
    conv->flags.basic = false;

    for (; c <= '0';) {
      // FIXME: We might be able to speed this up reusing the lookup table from
      // above. It might require changing Flags to be a plain integer where we
      // can |= a value.
      switch (c) {
        case '-':
          conv->flags.left = true;
          break;
        case '+':
          conv->flags.show_pos = true;
          break;
        case ' ':
          conv->flags.sign_col = true;
          break;
        case '#':
          conv->flags.alt = true;
          break;
        case '0':
          conv->flags.zero = true;
          break;
        default:
          goto flags_done;
      }
      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
    }
flags_done:

    if (c <= '9') {
      if (c >= '0') {
        int maybe_width = parse_digits();
        if (!is_positional && c == '$') {
          if (ABSL_PREDICT_FALSE(*next_arg != 0)) return nullptr;
          // Positional conversion.
          *next_arg = -1;
          conv->flags = Flags();
          conv->flags.basic = true;
          return ConsumeConversion<true>(original_pos, end, conv, next_arg);
        }
        conv->width.set_value(maybe_width);
      } else if (c == '*') {
        ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
        if (is_positional) {
          if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
          conv->width.set_from_arg(parse_digits());
          if (ABSL_PREDICT_FALSE(c != '$')) return nullptr;
          ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
        } else {
          conv->width.set_from_arg(++*next_arg);
        }
      }
    }

    if (c == '.') {
      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
      if (std::isdigit(c)) {
        conv->precision.set_value(parse_digits());
      } else if (c == '*') {
        ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
        if (is_positional) {
          if (ABSL_PREDICT_FALSE(c < '1' || c > '9')) return nullptr;
          conv->precision.set_from_arg(parse_digits());
          if (c != '$') return nullptr;
          ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
        } else {
          conv->precision.set_from_arg(++*next_arg);
        }
      } else {
        conv->precision.set_value(0);
      }
    }
  }

  auto tag = GetTagForChar(c);

  if (ABSL_PREDICT_FALSE(!tag.is_conv())) {
    if (ABSL_PREDICT_FALSE(!tag.is_length())) return nullptr;

    // It is a length modifier.
    using str_format_internal::LengthMod;
    LengthMod length_mod = tag.as_length();
    ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
    if (c == 'h' && length_mod == LengthMod::h) {
      conv->length_mod = LengthMod::hh;
      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
    } else if (c == 'l' && length_mod == LengthMod::l) {
      conv->length_mod = LengthMod::ll;
      ABSL_FORMAT_PARSER_INTERNAL_GET_CHAR();
    } else {
      conv->length_mod = length_mod;
    }
    tag = GetTagForChar(c);
    if (ABSL_PREDICT_FALSE(!tag.is_conv())) return nullptr;
  }

  assert(CheckFastPathSetting(*conv));
  (void)(&CheckFastPathSetting);

  conv->conv = tag.as_conv();
  if (!is_positional) conv->arg_position = ++*next_arg;
  return pos;
}

}  // namespace

std::string LengthModToString(LengthMod v) {
  switch (v) {
    case LengthMod::h:
      return "h";
    case LengthMod::hh:
      return "hh";
    case LengthMod::l:
      return "l";
    case LengthMod::ll:
      return "ll";
    case LengthMod::L:
      return "L";
    case LengthMod::j:
      return "j";
    case LengthMod::z:
      return "z";
    case LengthMod::t:
      return "t";
    case LengthMod::q:
      return "q";
    case LengthMod::none:
      return "";
  }
  return "";
}

const char *ConsumeUnboundConversion(const char *p, const char *end,
                                     UnboundConversion *conv, int *next_arg) {
  if (*next_arg < 0) return ConsumeConversion<true>(p, end, conv, next_arg);
  return ConsumeConversion<false>(p, end, conv, next_arg);
}

struct ParsedFormatBase::ParsedFormatConsumer {
  explicit ParsedFormatConsumer(ParsedFormatBase *parsedformat)
      : parsed(parsedformat), data_pos(parsedformat->data_.get()) {}

  bool Append(string_view s) {
    if (s.empty()) return true;

    size_t text_end = AppendText(s);

    if (!parsed->items_.empty() && !parsed->items_.back().is_conversion) {
      // Let's extend the existing text run.
      parsed->items_.back().text_end = text_end;
    } else {
      // Let's make a new text run.
      parsed->items_.push_back({false, text_end, {}});
    }
    return true;
  }

  bool ConvertOne(const UnboundConversion &conv, string_view s) {
    size_t text_end = AppendText(s);
    parsed->items_.push_back({true, text_end, conv});
    return true;
  }

  size_t AppendText(string_view s) {
    memcpy(data_pos, s.data(), s.size());
    data_pos += s.size();
    return static_cast<size_t>(data_pos - parsed->data_.get());
  }

  ParsedFormatBase *parsed;
  char* data_pos;
};

ParsedFormatBase::ParsedFormatBase(
    string_view format, bool allow_ignored,
    std::initializer_list<FormatConversionCharSet> convs)
    : data_(format.empty() ? nullptr : new char[format.size()]) {
  has_error_ = !ParseFormatString(format, ParsedFormatConsumer(this)) ||
               !MatchesConversions(allow_ignored, convs);
}

bool ParsedFormatBase::MatchesConversions(
    bool allow_ignored,
    std::initializer_list<FormatConversionCharSet> convs) const {
  std::unordered_set<int> used;
  auto add_if_valid_conv = [&](int pos, char c) {
      if (static_cast<size_t>(pos) > convs.size() ||
          !Contains(convs.begin()[pos - 1], c))
        return false;
      used.insert(pos);
      return true;
  };
  for (const ConversionItem &item : items_) {
    if (!item.is_conversion) continue;
    auto &conv = item.conv;
    if (conv.precision.is_from_arg() &&
        !add_if_valid_conv(conv.precision.get_from_arg(), '*'))
      return false;
    if (conv.width.is_from_arg() &&
        !add_if_valid_conv(conv.width.get_from_arg(), '*'))
      return false;
    if (!add_if_valid_conv(conv.arg_position,
                           FormatConversionCharToChar(conv.conv)))
      return false;
  }
  return used.size() == convs.size() || allow_ignored;
}

}  // namespace str_format_internal
ABSL_NAMESPACE_END
}  // namespace absl