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contexts.py
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from __future__ import annotations
import ast as stdlib_ast
import functools
import sys
from contextlib import contextmanager, suppress
from copy import copy
from . import buffering, color, tokenizing
from .ast import AST
from .collections import OrderedSet as oset
from .exceptions import (
FailedCut,
FailedExpectingEndOfText,
FailedKeywordSemantics,
FailedLeftRecursion,
FailedLookahead,
FailedParse,
FailedPattern,
FailedRef,
FailedSemantics,
FailedToken,
OptionSucceeded,
ParseError,
)
from .infos import (
Alert,
MemoKey,
ParseInfo,
ParserConfig,
ParseState,
RuleInfo,
RuleResult,
)
from .tokenizing import Tokenizer
from .util import (
info,
is_list,
left_assoc,
prune_dict,
right_assoc,
safe_name,
trim,
)
from .util.unicode_characters import (
C_CUT,
C_ENTRY,
C_FAILURE,
C_RECURSION,
C_SUCCESS,
)
__all__ = ['ParseContext', 'tatsumasu', 'leftrec', 'nomemo']
# decorator for rule implementation methods
def tatsumasu(*params, **kwparams):
def decorator(impl):
@functools.wraps(impl)
def wrapper(self):
name = impl.__name__
# remove the single leading and trailing underscore
# that the parser generator added
name = name[1:-1]
is_leftrec = getattr(impl, 'is_leftrec', False)
is_memoizable = getattr(impl, 'is_memoizable', True)
is_name = getattr(impl, 'is_name', False)
ruleinfo = RuleInfo(
name,
impl,
is_leftrec,
is_memoizable,
is_name,
params,
kwparams,
)
return self._call(ruleinfo)
return wrapper
return decorator
# This is used to mark left recursive rules
def leftrec(impl):
impl.is_leftrec = True
impl.is_memoizable = False
return impl
# Marks rules for which memoization has to be turned off
# (has no effect when left recursion is turned off)
def nomemo(impl):
impl.is_memoizable = False
return impl
# Marks rules marked as @name in the grammar
def isname(impl):
impl.is_name = True
return impl
class closure(list): # noqa: FURB189
def __hash__(self):
return hash(tuple(self))
class ParseContext:
def __init__(self, /, config: ParserConfig | None = None, **settings):
super().__init__()
config = ParserConfig.new(config, **settings)
self.config = config
self._active_config = self.config
self._tokenizer: Tokenizer | None = None
self._semantics = config.semantics
self._initialize_caches()
def _initialize_caches(self):
self._statestack = [ParseState()]
self._rule_stack = []
self._cut_stack = [False]
self._last_node = None
self.substate = None
self._lookahead = 0
self._furthest_exception = None
self._clear_memoization_caches()
@property
def active_config(self):
return self._active_config
@property
def semantics(self):
return self._semantics
@property
def encoding(self):
return self.active_config.encoding
@property
def parseinfo(self):
return self.active_config.parseinfo
@property
def trace(self):
return self.active_config.trace
@property
def trace_length(self):
return self.active_config.trace_length
@property
def trace_separator(self):
return self.active_config.trace_separator
@property
def trace_filename(self):
return self.active_config.trace_filename
@property
def comments_re(self):
return self.active_config.comments_re
@property
def eol_comments_re(self):
return self.active_config.eol_comments_re
@property
def whitespace(self):
return self.active_config.whitespace
@property
def ignorecase(self):
return self.active_config.ignorecase
@property
def nameguard(self):
return self.active_config.nameguard
@property
def memoize_lookaheads(self):
return self.active_config.memoize_lookaheads
@property
def left_recursion(self):
return self.active_config.left_recursion
@property
def colorize(self):
return self.active_config.colorize
@property
def keywords(self):
return self._keywords
@property
def namechars(self):
return self.active_config.namechars
def _reset(self, config: ParserConfig):
if self.active_config.colorize:
color.init()
self._initialize_caches()
self._keywords = oset(config.keywords)
self._semantics = config.semantics
if hasattr(self.semantics, 'set_context'):
self.semantics.set_context(self)
return config
def _set_furthest_exception(self, e):
if (
not self._furthest_exception
or e.pos > self._furthest_exception.pos
):
self._furthest_exception = e
def parse(self, text, /, config: ParserConfig | None = None, **settings):
config = self.config.replace_config(config)
config = config.replace(**settings)
self._active_config = config
self._reset(config)
if isinstance(text, tokenizing.Tokenizer):
tokenizer = text
elif text is not None:
cls = self.tokenizercls
tokenizer = cls(text, config=config)
else:
raise ParseError('No tokenizer or text')
self._tokenizer = tokenizer
start = self.active_config.effective_rule_name() or 'start'
try:
rule = self._find_rule(start)
return rule()
except FailedCut as e:
self._set_furthest_exception(e.nested)
raise self._furthest_exception from e
except FailedParse as e:
self._set_furthest_exception(e)
raise self._furthest_exception from e
finally:
self._clear_memoization_caches()
@property
def tokenizer(self):
return self._tokenizer
@property
def tokenizercls(self) -> type[Tokenizer]:
if self.config.tokenizercls is None:
return buffering.Buffer
else:
return self.config.tokenizercls
@property
def last_node(self):
return self._last_node
@last_node.setter
def last_node(self, value):
self._last_node = value
@property
def _pos(self):
return self._tokenizer.pos
def _clear_memoization_caches(self):
self._memos = {}
self._results = {}
self._recursion_depth = 0
def _goto(self, pos):
self._tokenizer.goto(pos)
def _next(self):
return self._tokenizer.next()
def _next_token(self, ruleinfo=None):
if ruleinfo is None or not ruleinfo.name.lstrip('_')[:1].isupper():
self._tokenizer.next_token()
def _define(self, keys, list_keys=None):
# if self.ast and isinstance(self.ast, AST):
ast = AST()
ast._define(keys, list_keys=list_keys)
ast.update(self.ast)
self.ast = ast
@property
def state(self):
return self._statestack[-1]
@property
def ast(self):
return self.state.ast
@ast.setter
def ast(self, value):
self.state.ast = value
def name_last_node(self, name):
self.ast[name] = self.last_node
def add_last_node_to_name(self, name):
self.ast._setlist(name, self.last_node)
@staticmethod
def _safe_name(name, ast):
while name in ast:
name += '_'
return name
def ast_set(self, name, value, as_list=False):
ast = self.ast
name = self._safe_name(name, ast)
previous = ast.get(name)
if previous is None:
new_value = [value] if as_list else value
elif is_list(previous):
new_value = [*previous, value]
else:
new_value = [previous, value]
ast = AST(ast, name=new_value)
self.ast = ast
def ast_append(self, name, value):
self.ast_set(name, value, as_list=True)
def _push_ast(self, copyast=False):
ast = copy(self.ast) if copyast else AST()
self.state.pos = self._pos
self._statestack.append(ParseState(ast=ast, pos=self._pos))
def _pop_ast(self):
self._statestack.pop()
self.tokenizer.goto(self.state.pos)
def _merge_ast(self):
pos = self._pos
ast = self.ast
cst = self.cst
self._statestack.pop()
self.ast = ast
self._extend_cst(cst)
self.tokenizer.goto(pos)
@property
def cst(self):
return self.state.cst
@cst.setter
def cst(self, value):
self.state.cst = value
def _push_cst(self):
self._statestack.append(ParseState(ast=self.ast))
def _pop_cst(self):
ast = self.ast
self._statestack.pop()
self.ast = ast
def _merge_cst(self, extend=True):
cst = self.cst
self._pop_cst()
if extend:
self._extend_cst(cst)
else:
self._append_cst(cst)
return cst
def _append_cst(self, node):
self.last_node = node
previous = self.cst
if previous is None:
self.cst = self._copy_node(node)
elif is_list(previous):
previous.append(node)
else:
self.cst = [previous, node]
return node
def _extend_cst(self, node):
self.last_node = node
if node is None:
return None
previous = self.cst
if previous is None:
self.cst = self._copy_node(node)
elif is_list(node):
if is_list(previous):
previous.extend(node)
else:
self.cst = [previous, *node]
elif is_list(previous):
previous.append(node)
else:
self.cst = [previous, node]
return node
def _copy_node(self, node):
if node is None:
return None
elif is_list(node):
return node[:]
else:
return node
def _is_cut_set(self):
return self._cut_stack[-1]
def _cut(self):
self._trace_cut()
self._cut_stack[-1] = True
# Kota Mizushima et al say that we can throw away
# memos for previous positions in the tokenizer under
# certain circumstances, without affecting the linearity
# of PEG parsing.
# https://kmizu.github.io/papers/paste513-mizushima.pdf
#
# We adopt the heuristic of always dropping the cache for
# positions less than the current cut position. It remains to
# be proven if doing it this way affects linearity. Empirically,
# it hasn't.
def prune(cache, cutpos):
prune_dict(cache, lambda k, _: k[0] < cutpos)
prune(self._memos, self._pos)
def _memoization(self):
return self.memoize_lookaheads or self._lookahead == 0
def _rulestack(self):
rulestack = [r.name for r in reversed(self._rule_stack)]
stack = self.trace_separator.join(rulestack)
if max(len(s) for s in stack.splitlines()) > self.trace_length:
stack = stack[: self.trace_length]
stack = stack.rsplit(self.trace_separator, 1)[0]
stack += self.trace_separator
return stack
def _find_rule(self, name):
self._error(name, exclass=FailedRef)
return lambda: None # makes static checkers happy
def _find_semantic_action(self, name):
if self.semantics is None:
return None, None
postproc = getattr(self.semantics, '_postproc', None)
action = getattr(self.semantics, safe_name(name), None)
if not callable(action):
action = getattr(self.semantics, '_default', None)
if not callable(action):
action = None
if not callable(postproc):
postproc = None
return action, postproc
def _trace(self, msg, *params, **kwargs):
if self.trace:
msg %= params
info(str(msg), file=sys.stderr)
def _trace_event(self, event):
if self.trace:
fname = ''
if self.trace_filename:
fname = self._tokenizer.line_info().filename + '\n'
lookahead = self._tokenizer.lookahead().rstrip()
if lookahead:
lookahead = '\n' + lookahead
self._trace(
'%s %s%s%s',
event + self._rulestack(),
self._tokenizer.lookahead_pos(),
color.Style.DIM + fname,
color.Style.NORMAL + lookahead + color.Style.RESET_ALL,
end='',
)
def _trace_entry(self):
self._trace_event(color.Fore.YELLOW + color.Style.BRIGHT + C_ENTRY)
def _trace_success(self):
self._trace_event(color.Fore.GREEN + color.Style.BRIGHT + C_SUCCESS)
def _trace_failure(self, ex=None):
if isinstance(ex, FailedLeftRecursion):
self._trace_recursion()
else:
self._trace_event(color.Fore.RED + color.Style.BRIGHT + C_FAILURE)
def _trace_recursion(self):
self._trace_event(color.Fore.RED + color.Style.BRIGHT + C_RECURSION)
def _trace_cut(self):
self._trace_event(color.Fore.MAGENTA + color.Style.BRIGHT + C_CUT)
def _trace_match(self, token, name=None, failed=False):
if self.trace:
fname = ''
if self.trace_filename:
fname = self._tokenizer.line_info().filename + '\n'
name = f'/{name}/' if name else ''
if not failed:
fgcolor = color.Fore.GREEN + C_SUCCESS
else:
fgcolor = color.Fore.RED + C_FAILURE
lookahead = self._tokenizer.lookahead().rstrip()
if lookahead:
lookahead = '\n' + lookahead
self._trace(
color.Style.BRIGHT + fgcolor + "'%s' %s%s%s",
token,
name,
color.Style.DIM + fname,
color.Style.NORMAL + lookahead + color.Style.RESET_ALL,
end='',
)
def _make_exception(self, item, exclass=FailedParse):
rulestack = (r.name for r in self._rule_stack[::-1])
return exclass(self.tokenizer, rulestack, item)
def _error(self, item, exclass=FailedParse):
raise self._make_exception(item, exclass=exclass)
def _fail(self):
self._error('fail')
def _get_parseinfo(self, name, pos):
endpos = self._pos
return ParseInfo(
tokenizer=self.tokenizer,
rule=name,
pos=pos,
endpos=endpos,
line=self.tokenizer.posline(pos),
endline=self.tokenizer.posline(endpos),
alerts=self.state.alerts,
)
@property
def rule(self):
return self._rule_stack[-1]
@property
def memokey(self):
return MemoKey(self._pos, self.rule, self.substate)
def _memoize(self, key, memo):
if self._memoization() and key.rule.is_memoizable:
self._memos[key] = memo
return memo
def _forget(self, key):
self._memos.pop(key, None)
def _memo_for(self, key):
return self._memos.get(key)
# if isinstance(memo, FailedLeftRecursion):
# memo = self._results.get(key, memo)
def _mkresult(self, node):
return RuleResult(node, self._pos, self.substate)
def _save_result(self, key, result):
if is_list(result.node):
result = RuleResult(
closure(result.node), result.newpos, result.newstate,
)
self._results[key] = result
def _is_recursive(self, ruleinfo):
return ruleinfo.is_leftrec
def _set_left_recursion_guard(self, key):
ex = self._make_exception(key.rule.name, exclass=FailedLeftRecursion)
self._memoize(key, ex)
def _call(self, ruleinfo):
self._rule_stack += [ruleinfo]
pos = self._pos
try:
self._trace_entry()
self._last_node = None
result = self._recursive_call(ruleinfo)
node, newpos, newstate = result
self._goto(newpos)
self.substate = newstate
self._append_cst(node)
self._trace_success()
return node
except FailedPattern:
self._error(f'Expecting <{ruleinfo.name}>')
except FailedParse as e:
self._goto(pos)
self._set_furthest_exception(e)
self._trace_failure(e)
raise
finally:
self._rule_stack.pop()
def _clear_recursion_errors(self):
def filter(key, value):
return isinstance(value, FailedLeftRecursion)
prune_dict(self._memos, filter)
def _recursive_call(self, ruleinfo):
self._next_token(ruleinfo)
key = self.memokey
if not ruleinfo.is_leftrec:
return self._invoke_rule(ruleinfo, key)
elif not self.left_recursion:
self._error('Left recursion detected', exclass=FailedLeftRecursion)
self._recursion_depth += 1
if key in self._results:
result = self._results[key]
else:
result = self._make_exception(
ruleinfo.name, exclass=FailedLeftRecursion,
)
self._results[key] = result
initial = self._pos
lastpos = initial - 1
while True:
try:
self._clear_recursion_errors()
new_result = self._invoke_rule(ruleinfo, key)
self._goto(initial)
except FailedParse:
break
if new_result.newpos > lastpos:
self._save_result(key, new_result)
lastpos = new_result.newpos
result = new_result
else:
break
self._recursion_depth -= 1
if isinstance(result, Exception):
raise result # pylint: disable=raising-non-exception
return result
def _invoke_rule(self, ruleinfo, key):
memo = self._memo_for(key)
if isinstance(memo, Exception):
raise memo
if memo:
return memo
self._set_left_recursion_guard(key)
self._push_ast()
try:
try:
self._next_token(ruleinfo)
ruleinfo.impl(self)
node = self._get_node(key.pos, ruleinfo)
node = self._invoke_semantic_rule(ruleinfo, node)
result = self._mkresult(node)
self._memoize(key, result)
return result
except FailedSemantics as e:
self._error(str(e))
except FailedParse as e:
self._memoize(key, e)
raise
finally:
self._pop_ast()
def _get_node(self, pos, ruleinfo):
node = self.ast
if not node:
node = tuple(self.cst) if is_list(self.cst) else self.cst
elif '@' in node:
node = node['@'] # override the AST
elif self.parseinfo:
node.set_parseinfo(self._get_parseinfo(ruleinfo.name, pos))
return node
def _invoke_semantic_rule(self, rule, node):
semantic_rule, postproc = self._find_semantic_action(rule.name)
if semantic_rule:
node = semantic_rule(
node, *(rule.params or ()), **(rule.kwparams or {}),
)
if callable(postproc):
postproc(self, node) # pylint: disable=not-callable
if rule.is_name:
self._check_name(node)
return node
def _token(self, token):
self._next_token()
if self.tokenizer.match(token) is None:
self._trace_match(token, failed=True)
self._error(token, exclass=FailedToken)
self._trace_match(token)
self._append_cst(token)
return token
def _constant(self, literal):
self._next_token()
self._trace_match(literal)
if isinstance(literal, str):
try:
literal = stdlib_ast.literal_eval(literal.strip())
except (ValueError, SyntaxError):
if '\n' in literal:
literal = trim(literal)
literal = eval( # noqa: S307
f'{"f" + repr(literal)}', {}, self.ast,
)
self._append_cst(literal)
return literal
def _alert(self, message, level):
self._next_token()
self._trace_match(f'{"^" * level}`{message}`', failed=True)
self.state.alerts.append(Alert(message=message, level=level))
def _pattern(self, pattern):
token = self.tokenizer.matchre(pattern)
if token is None:
self._trace_match('', pattern, failed=True)
self._error(pattern, exclass=FailedPattern)
self._trace_match(token, pattern)
self._append_cst(token)
return token
def _eof(self):
return self.tokenizer.atend()
def _eol(self):
return self.tokenizer.ateol()
def _check_eof(self):
self._next_token()
if not self.tokenizer.atend():
self._error(
'Expecting end of text', exclass=FailedExpectingEndOfText,
)
@contextmanager
def _try(self):
s = self.substate
self._push_ast(copyast=True)
self.last_node = None
try:
yield
self._merge_ast()
except FailedParse:
self._pop_ast()
self.substate = s
raise
@contextmanager
def _option(self):
self.last_node = None
self._cut_stack += [False]
try:
with self._try():
yield
raise OptionSucceeded()
except FailedCut:
raise
except FailedParse as e:
if self._is_cut_set():
raise FailedCut(e) from e
finally:
self._cut_stack.pop()
@contextmanager
def _choice(self):
self.last_node = None
with suppress(OptionSucceeded):
yield
@contextmanager
def _optional(self):
self.last_node = None
with self._choice(), self._option():
yield
@contextmanager
def _group(self):
self._push_cst()
try:
yield
self._merge_cst(extend=True)
except Exception:
self._pop_cst()
raise
@contextmanager
def _if(self):
s = self.substate
self._push_ast()
self._lookahead += 1
try:
yield
finally:
self._pop_ast() # simply discard
self._lookahead -= 1
self.substate = s
@contextmanager
def _ifnot(self):
try:
with self._if():
yield
except FailedParse:
pass
else:
self._error('', exclass=FailedLookahead)
def _isolate(self, block, drop=False):
self._push_cst()
try:
block()
cst = self.cst
finally:
self._pop_cst()
if is_list(cst):
cst = closure(cst)
if not drop:
self._append_cst(cst)
return cst
def _repeat(self, block, prefix=None, dropprefix=False):
while True:
with self._choice():
with self._option():
p = self._pos
if prefix:
self._isolate(prefix, drop=dropprefix)
self._cut()
self._isolate(block)
if self._pos == p:
self._error('empty closure')
return
def _closure(self, block, sep=None, omitsep=False):
self._push_cst()
try:
self.cst = []
with self._optional():
block()
self.cst = [self.cst]
self._repeat(block, prefix=sep, dropprefix=omitsep)
self.cst = closure(self.cst)
return self._merge_cst()
except Exception:
self._pop_cst()
raise
def _positive_closure(self, block, sep=None, omitsep=False):
self._push_cst()
try:
block()
self.cst = [self.cst]
self._repeat(block, prefix=sep, dropprefix=omitsep)
self.cst = closure(self.cst)
return self._merge_cst()
except Exception:
self._pop_cst()
raise
def _empty_closure(self):
cst = closure([])
self._append_cst(cst)
return cst
def _gather(self, block, sep):
return self._closure(block, sep=sep, omitsep=True)
def _positive_gather(self, block, sep):
return self._positive_closure(block, sep=sep, omitsep=True)
def _join(self, block, sep):
return self._closure(block, sep=sep)
def _positive_join(self, block, sep):
return self._positive_closure(block, sep=sep)
def _left_join(self, block, sep):
self.cst = left_assoc(self._positive_join(block, sep))
self.last_node = self.cst
return self.cst
def _right_join(self, block, sep):
self.cst = right_assoc(self._positive_join(block, sep))
self.last_node = self.cst
return self.cst
def _check_name(self, name):
name = str(name)
if self.ignorecase or self.tokenizer.ignorecase:
name = name.upper()
if name in self.keywords:
raise FailedKeywordSemantics(f'"{name}" is a reserved word')
def _void(self):
self.last_node = None
def _any(self):
c = self._next()
if c is None:
self._trace_match(c, failed=True)
self._error(c, exclass=FailedToken)
self._trace_match(c)
self._append_cst(c)
return c
def _skip_to(self, block):
while not self._eof():
try:
with self._if():
block()
except FailedParse:
pass
else:
break
pos = self._pos
self._next_token()
if self._pos == pos:
self._next()
block()