front_end/tokenizer.py

# Copyright 2019 Google LLC
#
# 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.

"""Tokenization for the Emboss definition language.

This module exports the tokenize function and various errors.

In addition, a couple of lists are exported for the use of
generate_grammar_md.py:

LITERAL_TOKEN_PATTERNS: A list of literal strings which are matched against
  input.
REGEX_TOKEN_PATTERNS: A list of regexes used for tokenization.
  REGEX_TOKEN_PATTERNS[n].regex is an re.RegexObject
  (REGEX_TOKEN_PATTERNS[n].regex.pattern contains the text of the pattern), and
  REGEX_TOKEN_PATTERNS[n].symbol is the name of the symbol assigned to tokens
  which match the pattern.
"""

import collections
import re

from util import error
from util import parser_types


def tokenize(text, file_name):
  # TODO(bolms): suppress end-of-line, indent, and dedent tokens between matched
  # delimiters ([], (), and {}).
  """Tokenizes its argument.

  Arguments:
    text: The raw text of a .emb file.
    file_name: The name of the file to use in errors.

  Returns:
    A tuple of:
      a list of parser_types.Tokens or None
      a possibly-empty list of errors.
  """
  tokens = []
  indent_stack = [""]
  line_number = 0
  for line in text.splitlines():
    line_number += 1

    # _tokenize_line splits the actual text into tokens.
    line_tokens, errors = _tokenize_line(line, line_number, file_name)
    if errors:
      return None, errors

    # Lines with only whitespace and comments are not used for Indent/Dedent
    # calculation, and do not produce end-of-line tokens.
    for token in line_tokens:
      if token.symbol != "Comment":
        break
    else:
      tokens.extend(line_tokens)
      tokens.append(parser_types.Token(
          '"\\n"', "\n", parser_types.make_location(
              (line_number, len(line) + 1), (line_number, len(line) + 1))))
      continue

    # Leading whitespace is whatever .lstrip() removes.
    leading_whitespace = line[0:len(line) - len(line.lstrip())]
    if leading_whitespace == indent_stack[-1]:
      # If the current leading whitespace is equal to the last leading
      # whitespace, do not emit an Indent or Dedent token.
      pass
    elif leading_whitespace.startswith(indent_stack[-1]):
      # If the current leading whitespace is longer than the last leading
      # whitespace, emit an Indent token.  For the token text, take the new
      # part of the whitespace.
      tokens.append(
          parser_types.Token(
              "Indent", leading_whitespace[len(indent_stack[-1]):],
              parser_types.make_location(
                  (line_number, len(indent_stack[-1]) + 1),
                  (line_number, len(leading_whitespace) + 1))))
      indent_stack.append(leading_whitespace)
    else:
      # Otherwise, search for the unclosed indentation level that matches
      # the current indentation level.  Emit a Dedent token for each
      # newly-closed indentation level.
      for i in range(len(indent_stack) - 1, -1, -1):
        if leading_whitespace == indent_stack[i]:
          break
        tokens.append(
            parser_types.Token("Dedent", "", parser_types.make_location(
                (line_number, len(leading_whitespace) + 1),
                (line_number, len(leading_whitespace) + 1))))
        del indent_stack[i]
      else:
        return None, [[error.error(
            file_name, parser_types.make_location(
                (line_number, 1), (line_number, len(leading_whitespace) + 1)),
            "Bad indentation")]]

    tokens.extend(line_tokens)

    # Append an end-of-line token (for non-whitespace lines).
    tokens.append(parser_types.Token(
        '"\\n"', "\n", parser_types.make_location(
            (line_number, len(line) + 1), (line_number, len(line) + 1))))
  for i in range(len(indent_stack) - 1):
    tokens.append(parser_types.Token("Dedent", "", parser_types.make_location(
        (line_number + 1, 1), (line_number + 1, 1))))
  return tokens, []

# Token patterns used by _tokenize_line.
LITERAL_TOKEN_PATTERNS = (
    "[ ] ( ) : = + - * . ? == != && || < > <= >= , "
    "$static_size_in_bits $is_statically_sized "
    "$max $present $upper_bound $lower_bound "
    "$size_in_bits $size_in_bytes "
    "$max_size_in_bits $max_size_in_bytes $min_size_in_bits $min_size_in_bytes "
    "$default struct bits enum external import as if let").split()
_T = collections.namedtuple("T", ["regex", "symbol"])
REGEX_TOKEN_PATTERNS = [
    # Words starting with variations of "emboss reserved" are reserved for
    # internal use by the Emboss compiler.
    _T(re.compile(r"EmbossReserved[A-Za-z0-9]*"), "BadWord"),
    _T(re.compile(r"emboss_reserved[_a-z0-9]*"), "BadWord"),
    _T(re.compile(r"EMBOSS_RESERVED[_A-Z0-9]*"), "BadWord"),
    _T(re.compile(r'"(?:[^"\n\\]|\\[n\\"])*"'), "String"),
    _T(re.compile("[0-9]+"), "Number"),
    _T(re.compile("[0-9]{1,3}(?:_[0-9]{3})*"), "Number"),
    _T(re.compile("0x[0-9a-fA-F]+"), "Number"),
    _T(re.compile("0x_?[0-9a-fA-F]{1,4}(?:_[0-9a-fA-F]{4})*"), "Number"),
    _T(re.compile("0x_?[0-9a-fA-F]{1,8}(?:_[0-9a-fA-F]{8})*"), "Number"),
    _T(re.compile("0b[01]+"), "Number"),
    _T(re.compile("0b_?[01]{1,4}(?:_[01]{4})*"), "Number"),
    _T(re.compile("0b_?[01]{1,8}(?:_[01]{8})*"), "Number"),
    _T(re.compile("true|false"), "BooleanConstant"),
    _T(re.compile("[a-z][a-z_0-9]*"), "SnakeWord"),
    # Single-letter ShoutyWords (like "A") and single-letter-followed-by-number
    # ShoutyWords ("A100") are disallowed due to ambiguity with CamelWords.  A
    # ShoutyWord must start with an upper case letter and contain at least one
    # more upper case letter or '_'.
    _T(re.compile("[A-Z][A-Z_0-9]*[A-Z_][A-Z_0-9]*"), "ShoutyWord"),
    # A CamelWord starts with A-Z and contains at least one a-z, and no _.
    _T(re.compile("[A-Z][a-zA-Z0-9]*[a-z][a-zA-Z0-9]*"), "CamelWord"),
    _T(re.compile("-- .*"), "Documentation"),
    _T(re.compile("--$"), "Documentation"),
    _T(re.compile("--.*"), "BadDocumentation"),
    _T(re.compile(r"\s+"), None),
    _T(re.compile("#.*"), "Comment"),
    # BadWord and BadNumber are a catch-alls for words and numbers so that
    # something like "abcDef" doesn't tokenize to [SnakeWord, CamelWord].
    #
    # This is preferable to returning an error because the BadWord and BadNumber
    # token types can be used in example-based errors.
    _T(re.compile("[0-9][bxBX]?[0-9a-fA-F_]*"), "BadNumber"),
    _T(re.compile("[a-zA-Z_$0-9]+"), "BadWord"),
]
del _T


def _tokenize_line(line, line_number, file_name):
  """Tokenizes a single line of input.

  Arguments:
    line: The line of text to tokenize.
    line_number: The line number (used when constructing token objects).
    file_name: The name of a file to use in errors.

  Returns:
    A tuple of:
      A list of token objects or None.
      A possibly-empty list of errors.
  """
  tokens = []
  offset = 0
  while offset < len(line):
    best_candidate = ""
    best_candidate_symbol = None
    # Find the longest match.  Ties go to the first match.  This way, keywords
    # ("struct") are matched as themselves, but words that only happen to start
    # with keywords ("structure") are matched as words.
    #
    # There is never a reason to try to match a literal after a regex that
    # could also match that literal, so check literals first.
    for literal in LITERAL_TOKEN_PATTERNS:
      if line[offset:].startswith(literal) and len(literal) > len(
          best_candidate):
        best_candidate = literal
        # For Emboss, the name of a literal token is just the literal in quotes,
        # so that the grammar can read a little more naturally, e.g.:
        #
        #     expression -> expression "+" expression
        #
        # instead of
        #
        #     expression -> expression Plus expression
        best_candidate_symbol = '"' + literal + '"'
    for pattern in REGEX_TOKEN_PATTERNS:
      match_result = pattern.regex.match(line[offset:])
      if match_result and len(match_result.group(0)) > len(best_candidate):
        best_candidate = match_result.group(0)
        best_candidate_symbol = pattern.symbol
    if not best_candidate:
      return None, [[error.error(
          file_name, parser_types.make_location(
              (line_number, offset + 1), (line_number, offset + 2)),
          "Unrecognized token")]]
    if best_candidate_symbol:
      tokens.append(parser_types.Token(
          best_candidate_symbol, best_candidate, parser_types.make_location(
              (line_number, offset + 1),
              (line_number, offset + len(best_candidate) + 1))))
    offset += len(best_candidate)
  return tokens, None