cpython/Tools/peg_generator/pegen/parser.py

import argparse
import sys
import time
import token
import tokenize
import traceback
from abc import abstractmethod
from typing import Any, Callable, ClassVar, Dict, Optional, Tuple, Type, TypeVar, cast

from pegen.tokenizer import Mark, Tokenizer, exact_token_types

T = TypeVar("T")
F = TypeVar("F", bound=Callable[..., Any])


def logger(method: F) -> F:
    """For non-memoized functions that we want to be logged.

    (In practice this is only non-leader left-recursive functions.)
    """
    method_name = method.__name__

    def logger_wrapper(self: "Parser", *args: object) -> Any:
        if not self._verbose:
            return method(self, *args)
        argsr = ",".join(repr(arg) for arg in args)
        fill = "  " * self._level
        print(f"{fill}{method_name}({argsr}) .... (looking at {self.showpeek()})")
        self._level += 1
        tree = method(self, *args)
        self._level -= 1
        print(f"{fill}... {method_name}({argsr}) --> {tree!s:.200}")
        return tree

    logger_wrapper.__wrapped__ = method  # type: ignore[attr-defined]
    return cast(F, logger_wrapper)


def memoize(method: F) -> F:
    """Memoize a symbol method."""
    method_name = method.__name__

    def memoize_wrapper(self: "Parser", *args: object) -> Any:
        mark = self._mark()
        key = mark, method_name, args
        # Fast path: cache hit, and not verbose.
        if key in self._cache and not self._verbose:
            tree, endmark = self._cache[key]
            self._reset(endmark)
            return tree
        # Slow path: no cache hit, or verbose.
        verbose = self._verbose
        argsr = ",".join(repr(arg) for arg in args)
        fill = "  " * self._level
        if key not in self._cache:
            if verbose:
                print(f"{fill}{method_name}({argsr}) ... (looking at {self.showpeek()})")
            self._level += 1
            tree = method(self, *args)
            self._level -= 1
            if verbose:
                print(f"{fill}... {method_name}({argsr}) -> {tree!s:.200}")
            endmark = self._mark()
            self._cache[key] = tree, endmark
        else:
            tree, endmark = self._cache[key]
            if verbose:
                print(f"{fill}{method_name}({argsr}) -> {tree!s:.200}")
            self._reset(endmark)
        return tree

    memoize_wrapper.__wrapped__ = method  # type: ignore[attr-defined]
    return cast(F, memoize_wrapper)


def memoize_left_rec(
    method: Callable[["Parser"], Optional[T]]
) -> Callable[["Parser"], Optional[T]]:
    """Memoize a left-recursive symbol method."""
    method_name = method.__name__

    def memoize_left_rec_wrapper(self: "Parser") -> Optional[T]:
        mark = self._mark()
        key = mark, method_name, ()
        # Fast path: cache hit, and not verbose.
        if key in self._cache and not self._verbose:
            tree, endmark = self._cache[key]
            self._reset(endmark)
            return tree
        # Slow path: no cache hit, or verbose.
        verbose = self._verbose
        fill = "  " * self._level
        if key not in self._cache:
            if verbose:
                print(f"{fill}{method_name} ... (looking at {self.showpeek()})")
            self._level += 1

            # For left-recursive rules we manipulate the cache and
            # loop until the rule shows no progress, then pick the
            # previous result.  For an explanation why this works, see
            # https://github.com/PhilippeSigaud/Pegged/wiki/Left-Recursion
            # (But we use the memoization cache instead of a static
            # variable; perhaps this is similar to a paper by Warth et al.
            # (http://web.cs.ucla.edu/~todd/research/pub.php?id=pepm08).

            # Prime the cache with a failure.
            self._cache[key] = None, mark
            lastresult, lastmark = None, mark
            depth = 0
            if verbose:
                print(f"{fill}Recursive {method_name} at {mark} depth {depth}")

            while True:
                self._reset(mark)
                self.in_recursive_rule += 1
                try:
                    result = method(self)
                finally:
                    self.in_recursive_rule -= 1
                endmark = self._mark()
                depth += 1
                if verbose:
                    print(
                        f"{fill}Recursive {method_name} at {mark} depth {depth}: {result!s:.200} to {endmark}"
                    )
                if not result:
                    if verbose:
                        print(f"{fill}Fail with {lastresult!s:.200} to {lastmark}")
                    break
                if endmark <= lastmark:
                    if verbose:
                        print(f"{fill}Bailing with {lastresult!s:.200} to {lastmark}")
                    break
                self._cache[key] = lastresult, lastmark = result, endmark

            self._reset(lastmark)
            tree = lastresult

            self._level -= 1
            if verbose:
                print(f"{fill}{method_name}() -> {tree!s:.200} [cached]")
            if tree:
                endmark = self._mark()
            else:
                endmark = mark
                self._reset(endmark)
            self._cache[key] = tree, endmark
        else:
            tree, endmark = self._cache[key]
            if verbose:
                print(f"{fill}{method_name}() -> {tree!s:.200} [fresh]")
            if tree:
                self._reset(endmark)
        return tree

    memoize_left_rec_wrapper.__wrapped__ = method  # type: ignore[attr-defined]
    return memoize_left_rec_wrapper


class Parser:
    """Parsing base class."""

    KEYWORDS: ClassVar[Tuple[str, ...]]

    SOFT_KEYWORDS: ClassVar[Tuple[str, ...]]

    def __init__(self, tokenizer: Tokenizer, *, verbose: bool = False):
        self._tokenizer = tokenizer
        self._verbose = verbose
        self._level = 0
        self._cache: Dict[Tuple[Mark, str, Tuple[Any, ...]], Tuple[Any, Mark]] = {}
        # Integer tracking whether we are in a left recursive rule or not. Can be useful
        # for error reporting.
        self.in_recursive_rule = 0
        # Pass through common tokenizer methods.
        self._mark = self._tokenizer.mark
        self._reset = self._tokenizer.reset

    @abstractmethod
    def start(self) -> Any:
        pass

    def showpeek(self) -> str:
        tok = self._tokenizer.peek()
        return f"{tok.start[0]}.{tok.start[1]}: {token.tok_name[tok.type]}:{tok.string!r}"

    @memoize
    def name(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.NAME and tok.string not in self.KEYWORDS:
            return self._tokenizer.getnext()
        return None

    @memoize
    def number(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.NUMBER:
            return self._tokenizer.getnext()
        return None

    @memoize
    def string(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.STRING:
            return self._tokenizer.getnext()
        return None

    @memoize
    def fstring_start(self) -> Optional[tokenize.TokenInfo]:
        FSTRING_START = getattr(token, "FSTRING_START")
        if not FSTRING_START:
            return None
        tok = self._tokenizer.peek()
        if tok.type == FSTRING_START:
            return self._tokenizer.getnext()
        return None

    @memoize
    def fstring_middle(self) -> Optional[tokenize.TokenInfo]:
        FSTRING_MIDDLE = getattr(token, "FSTRING_MIDDLE")
        if not FSTRING_MIDDLE:
            return None
        tok = self._tokenizer.peek()
        if tok.type == FSTRING_MIDDLE:
            return self._tokenizer.getnext()
        return None

    @memoize
    def fstring_end(self) -> Optional[tokenize.TokenInfo]:
        FSTRING_END = getattr(token, "FSTRING_END")
        if not FSTRING_END:
            return None
        tok = self._tokenizer.peek()
        if tok.type == FSTRING_END:
            return self._tokenizer.getnext()
        return None

    @memoize
    def op(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.OP:
            return self._tokenizer.getnext()
        return None

    @memoize
    def type_comment(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.TYPE_COMMENT:
            return self._tokenizer.getnext()
        return None

    @memoize
    def soft_keyword(self) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.type == token.NAME and tok.string in self.SOFT_KEYWORDS:
            return self._tokenizer.getnext()
        return None

    @memoize
    def expect(self, type: str) -> Optional[tokenize.TokenInfo]:
        tok = self._tokenizer.peek()
        if tok.string == type:
            return self._tokenizer.getnext()
        if type in exact_token_types:
            if tok.type == exact_token_types[type]:
                return self._tokenizer.getnext()
        if type in token.__dict__:
            if tok.type == token.__dict__[type]:
                return self._tokenizer.getnext()
        if tok.type == token.OP and tok.string == type:
            return self._tokenizer.getnext()
        return None

    def expect_forced(self, res: Any, expectation: str) -> Optional[tokenize.TokenInfo]:
        if res is None:
            raise self.make_syntax_error(f"expected {expectation}")
        return res

    def positive_lookahead(self, func: Callable[..., T], *args: object) -> T:
        mark = self._mark()
        ok = func(*args)
        self._reset(mark)
        return ok

    def negative_lookahead(self, func: Callable[..., object], *args: object) -> bool:
        mark = self._mark()
        ok = func(*args)
        self._reset(mark)
        return not ok

    def make_syntax_error(self, message: str, filename: str = "<unknown>") -> SyntaxError:
        tok = self._tokenizer.diagnose()
        return SyntaxError(message, (filename, tok.start[0], 1 + tok.start[1], tok.line))


def simple_parser_main(parser_class: Type[Parser]) -> None:
    argparser = argparse.ArgumentParser()
    argparser.add_argument(
        "-v",
        "--verbose",
        action="count",
        default=0,
        help="Print timing stats; repeat for more debug output",
    )
    argparser.add_argument(
        "-q", "--quiet", action="store_true", help="Don't print the parsed program"
    )
    argparser.add_argument("filename", help="Input file ('-' to use stdin)")

    args = argparser.parse_args()
    verbose = args.verbose
    verbose_tokenizer = verbose >= 3
    verbose_parser = verbose == 2 or verbose >= 4

    t0 = time.time()

    filename = args.filename
    if filename == "" or filename == "-":
        filename = "<stdin>"
        file = sys.stdin
    else:
        file = open(args.filename)
    try:
        tokengen = tokenize.generate_tokens(file.readline)
        tokenizer = Tokenizer(tokengen, verbose=verbose_tokenizer)
        parser = parser_class(tokenizer, verbose=verbose_parser)
        tree = parser.start()
        try:
            if file.isatty():
                endpos = 0
            else:
                endpos = file.tell()
        except IOError:
            endpos = 0
    finally:
        if file is not sys.stdin:
            file.close()

    t1 = time.time()

    if not tree:
        err = parser.make_syntax_error(filename)
        traceback.print_exception(err.__class__, err, None)
        sys.exit(1)

    if not args.quiet:
        print(tree)

    if verbose:
        dt = t1 - t0
        diag = tokenizer.diagnose()
        nlines = diag.end[0]
        if diag.type == token.ENDMARKER:
            nlines -= 1
        print(f"Total time: {dt:.3f} sec; {nlines} lines", end="")
        if endpos:
            print(f" ({endpos} bytes)", end="")
        if dt:
            print(f"; {nlines / dt:.0f} lines/sec")
        else:
            print()
        print("Caches sizes:")
        print(f"  token array : {len(tokenizer._tokens):10}")
        print(f"        cache : {len(parser._cache):10}")
        ## print_memstats()