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import contextlib import re from dataclasses import dataclass from typing import Dict, Iterator, NoReturn, Optional, Tuple, Union from .specifiers import Specifier @dataclass class Token: name: str text: str position: int class ParserSyntaxError(Exception): """The provided source text could not be parsed correctly.""" def __init__( self, message: str, *, source: str, span: Tuple[int, int], ) -> None: self.span = span self.message = message self.source = source super().__init__() def __str__(self) -> str: marker = " " * self.span[0] + "~" * (self.span[1] - self.span[0]) + "^" return "\n ".join([self.message, self.source, marker]) DEFAULT_RULES: "Dict[str, Union[str, re.Pattern[str]]]" = { "LEFT_PARENTHESIS": r"\(", "RIGHT_PARENTHESIS": r"\)", "LEFT_BRACKET": r"\[", "RIGHT_BRACKET": r"\]", "SEMICOLON": r";", "COMMA": r",", "QUOTED_STRING": re.compile( r""" ( ('[^']*') | ("[^"]*") ) """, re.VERBOSE, ), "OP": r"(===|==|~=|!=|<=|>=|<|>)", "BOOLOP": r"\b(or|and)\b", "IN": r"\bin\b", "NOT": r"\bnot\b", "VARIABLE": re.compile( r""" \b( python_version |python_full_version |os[._]name |sys[._]platform |platform_(release|system) |platform[._](version|machine|python_implementation) |python_implementation |implementation_(name|version) |extra )\b """, re.VERBOSE, ), "SPECIFIER": re.compile( Specifier._operator_regex_str + Specifier._version_regex_str, re.VERBOSE | re.IGNORECASE, ), "AT": r"\@", "URL": r"[^ \t]+", "IDENTIFIER": r"\b[a-zA-Z0-9][a-zA-Z0-9._-]*\b", "WS": r"[ \t]+", "END": r"$", } class Tokenizer: """Context-sensitive token parsing. Provides methods to examine the input stream to check whether the next token matches. """ def __init__( self, source: str, *, rules: "Dict[str, Union[str, re.Pattern[str]]]", ) -> None: self.source = source self.rules: Dict[str, re.Pattern[str]] = { name: re.compile(pattern) for name, pattern in rules.items() } self.next_token: Optional[Token] = None self.position = 0 def consume(self, name: str) -> None: """Move beyond provided token name, if at current position.""" if self.check(name): self.read() def check(self, name: str, *, peek: bool = False) -> bool: """Check whether the next token has the provided name. By default, if the check succeeds, the token *must* be read before another check. If `peek` is set to `True`, the token is not loaded and would need to be checked again. """ assert ( self.next_token is None ), f"Cannot check for {name!r}, already have {self.next_token!r}" assert name in self.rules, f"Unknown token name: {name!r}" expression = self.rules[name] match = expression.match(self.source, self.position) if match is None: return False if not peek: self.next_token = Token(name, match[0], self.position) return True def expect(self, name: str, *, expected: str) -> Token: """Expect a certain token name next, failing with a syntax error otherwise. The token is *not* read. """ if not self.check(name): raise self.raise_syntax_error(f"Expected {expected}") return self.read() def read(self) -> Token: """Consume the next token and return it.""" token = self.next_token assert token is not None self.position += len(token.text) self.next_token = None return token def raise_syntax_error( self, message: str, *, span_start: Optional[int] = None, span_end: Optional[int] = None, ) -> NoReturn: """Raise ParserSyntaxError at the given position.""" span = ( self.position if span_start is None else span_start, self.position if span_end is None else span_end, ) raise ParserSyntaxError( message, source=self.source, span=span, ) @contextlib.contextmanager def enclosing_tokens(self, open_token: str, close_token: str) -> Iterator[bool]: if self.check(open_token): open_position = self.position self.read() else: open_position = None yield open_position is not None if open_position is None: return if not self.check(close_token): self.raise_syntax_error( f"Expected closing {close_token}", span_start=open_position, ) self.read()