djavu-asus/elpy/rpc-venv/lib/python3.11/site-packages/blib2to3/pgen2/parse.py

   1 # Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
   2 # Licensed to PSF under a Contributor Agreement.
   3
   4 """Parser engine for the grammar tables generated by pgen.
   5
   6 The grammar table must be loaded first.
   7
   8 See Parser/parser.c in the Python distribution for additional info on
   9 how this parsing engine works.
  10
  11 """
  12 from contextlib import contextmanager
  13 from typing import (
  14     TYPE_CHECKING,
  15     Any,
  16     Callable,
  17     Dict,
  18     Iterator,
  19     List,
  20     Optional,
  21     Set,
  22     Tuple,
  23     Union,
  24     cast,
  25 )
  26
  27 from blib2to3.pgen2.grammar import Grammar
  28 from blib2to3.pytree import NL, Context, Leaf, Node, RawNode, convert
  29
  30 # Local imports
  31 from . import grammar, token, tokenize
  32
  33 if TYPE_CHECKING:
  34     from blib2to3.pgen2.driver import TokenProxy
  35
  36
  37 Results = Dict[str, NL]
  38 Convert = Callable[[Grammar, RawNode], Union[Node, Leaf]]
  39 DFA = List[List[Tuple[int, int]]]
  40 DFAS = Tuple[DFA, Dict[int, int]]
  41
  42
  43 def lam_sub(grammar: Grammar, node: RawNode) -> NL:
  44     assert node[3] is not None
  45     return Node(type=node[0], children=node[3], context=node[2])
  46
  47
  48 # A placeholder node, used when parser is backtracking.
  49 DUMMY_NODE = (-1, None, None, None)
  50
  51
  52 def stack_copy(
  53     stack: List[Tuple[DFAS, int, RawNode]]
  54 ) -> List[Tuple[DFAS, int, RawNode]]:
  55     """Nodeless stack copy."""
  56     return [(dfa, label, DUMMY_NODE) for dfa, label, _ in stack]
  57
  58
  59 class Recorder:
  60     def __init__(self, parser: "Parser", ilabels: List[int], context: Context) -> None:
  61         self.parser = parser
  62         self._ilabels = ilabels
  63         self.context = context  # not really matter
  64
  65         self._dead_ilabels: Set[int] = set()
  66         self._start_point = self.parser.stack
  67         self._points = {ilabel: stack_copy(self._start_point) for ilabel in ilabels}
  68
  69     @property
  70     def ilabels(self) -> Set[int]:
  71         return self._dead_ilabels.symmetric_difference(self._ilabels)
  72
  73     @contextmanager
  74     def switch_to(self, ilabel: int) -> Iterator[None]:
  75         with self.backtrack():
  76             self.parser.stack = self._points[ilabel]
  77             try:
  78                 yield
  79             except ParseError:
  80                 self._dead_ilabels.add(ilabel)
  81             finally:
  82                 self.parser.stack = self._start_point
  83
  84     @contextmanager
  85     def backtrack(self) -> Iterator[None]:
  86         """
  87         Use the node-level invariant ones for basic parsing operations (push/pop/shift).
  88         These still will operate on the stack; but they won't create any new nodes, or
  89         modify the contents of any other existing nodes.
  90
  91         This saves us a ton of time when we are backtracking, since we
  92         want to restore to the initial state as quick as possible, which
  93         can only be done by having as little mutatations as possible.
  94         """
  95         is_backtracking = self.parser.is_backtracking
  96         try:
  97             self.parser.is_backtracking = True
  98             yield
  99         finally:
 100             self.parser.is_backtracking = is_backtracking
 101
 102     def add_token(self, tok_type: int, tok_val: str, raw: bool = False) -> None:
 103         func: Callable[..., Any]
 104         if raw:
 105             func = self.parser._addtoken
 106         else:
 107             func = self.parser.addtoken
 108
 109         for ilabel in self.ilabels:
 110             with self.switch_to(ilabel):
 111                 args = [tok_type, tok_val, self.context]
 112                 if raw:
 113                     args.insert(0, ilabel)
 114                 func(*args)
 115
 116     def determine_route(
 117         self, value: Optional[str] = None, force: bool = False
 118     ) -> Optional[int]:
 119         alive_ilabels = self.ilabels
 120         if len(alive_ilabels) == 0:
 121             *_, most_successful_ilabel = self._dead_ilabels
 122             raise ParseError("bad input", most_successful_ilabel, value, self.context)
 123
 124         ilabel, *rest = alive_ilabels
 125         if force or not rest:
 126             return ilabel
 127         else:
 128             return None
 129
 130
 131 class ParseError(Exception):
 132     """Exception to signal the parser is stuck."""
 133
 134     def __init__(
 135         self, msg: str, type: Optional[int], value: Optional[str], context: Context
 136     ) -> None:
 137         Exception.__init__(
 138             self, f"{msg}: type={type!r}, value={value!r}, context={context!r}"
 139         )
 140         self.msg = msg
 141         self.type = type
 142         self.value = value
 143         self.context = context
 144
 145
 146 class Parser:
 147     """Parser engine.
 148
 149     The proper usage sequence is:
 150
 151     p = Parser(grammar, [converter])  # create instance
 152     p.setup([start])                  # prepare for parsing
 153     <for each input token>:
 154         if p.addtoken(...):           # parse a token; may raise ParseError
 155             break
 156     root = p.rootnode                 # root of abstract syntax tree
 157
 158     A Parser instance may be reused by calling setup() repeatedly.
 159
 160     A Parser instance contains state pertaining to the current token
 161     sequence, and should not be used concurrently by different threads
 162     to parse separate token sequences.
 163
 164     See driver.py for how to get input tokens by tokenizing a file or
 165     string.
 166
 167     Parsing is complete when addtoken() returns True; the root of the
 168     abstract syntax tree can then be retrieved from the rootnode
 169     instance variable.  When a syntax error occurs, addtoken() raises
 170     the ParseError exception.  There is no error recovery; the parser
 171     cannot be used after a syntax error was reported (but it can be
 172     reinitialized by calling setup()).
 173
 174     """
 175
 176     def __init__(self, grammar: Grammar, convert: Optional[Convert] = None) -> None:
 177         """Constructor.
 178
 179         The grammar argument is a grammar.Grammar instance; see the
 180         grammar module for more information.
 181
 182         The parser is not ready yet for parsing; you must call the
 183         setup() method to get it started.
 184
 185         The optional convert argument is a function mapping concrete
 186         syntax tree nodes to abstract syntax tree nodes.  If not
 187         given, no conversion is done and the syntax tree produced is
 188         the concrete syntax tree.  If given, it must be a function of
 189         two arguments, the first being the grammar (a grammar.Grammar
 190         instance), and the second being the concrete syntax tree node
 191         to be converted.  The syntax tree is converted from the bottom
 192         up.
 193
 194         **post-note: the convert argument is ignored since for Black's
 195         usage, convert will always be blib2to3.pytree.convert. Allowing
 196         this to be dynamic hurts mypyc's ability to use early binding.
 197         These docs are left for historical and informational value.
 198
 199         A concrete syntax tree node is a (type, value, context, nodes)
 200         tuple, where type is the node type (a token or symbol number),
 201         value is None for symbols and a string for tokens, context is
 202         None or an opaque value used for error reporting (typically a
 203         (lineno, offset) pair), and nodes is a list of children for
 204         symbols, and None for tokens.
 205
 206         An abstract syntax tree node may be anything; this is entirely
 207         up to the converter function.
 208
 209         """
 210         self.grammar = grammar
 211         # See note in docstring above. TL;DR this is ignored.
 212         self.convert = convert or lam_sub
 213         self.is_backtracking = False
 214
 215     def setup(self, proxy: "TokenProxy", start: Optional[int] = None) -> None:
 216         """Prepare for parsing.
 217
 218         This *must* be called before starting to parse.
 219
 220         The optional argument is an alternative start symbol; it
 221         defaults to the grammar's start symbol.
 222
 223         You can use a Parser instance to parse any number of programs;
 224         each time you call setup() the parser is reset to an initial
 225         state determined by the (implicit or explicit) start symbol.
 226
 227         """
 228         if start is None:
 229             start = self.grammar.start
 230         # Each stack entry is a tuple: (dfa, state, node).
 231         # A node is a tuple: (type, value, context, children),
 232         # where children is a list of nodes or None, and context may be None.
 233         newnode: RawNode = (start, None, None, [])
 234         stackentry = (self.grammar.dfas[start], 0, newnode)
 235         self.stack: List[Tuple[DFAS, int, RawNode]] = [stackentry]
 236         self.rootnode: Optional[NL] = None
 237         self.used_names: Set[str] = set()
 238         self.proxy = proxy
 239
 240     def addtoken(self, type: int, value: str, context: Context) -> bool:
 241         """Add a token; return True iff this is the end of the program."""
 242         # Map from token to label
 243         ilabels = self.classify(type, value, context)
 244         assert len(ilabels) >= 1
 245
 246         # If we have only one state to advance, we'll directly
 247         # take it as is.
 248         if len(ilabels) == 1:
 249             [ilabel] = ilabels
 250             return self._addtoken(ilabel, type, value, context)
 251
 252         # If there are multiple states which we can advance (only
 253         # happen under soft-keywords), then we will try all of them
 254         # in parallel and as soon as one state can reach further than
 255         # the rest, we'll choose that one. This is a pretty hacky
 256         # and hopefully temporary algorithm.
 257         #
 258         # For a more detailed explanation, check out this post:
 259         # https://tree.science/what-the-backtracking.html
 260
 261         with self.proxy.release() as proxy:
 262             counter, force = 0, False
 263             recorder = Recorder(self, ilabels, context)
 264             recorder.add_token(type, value, raw=True)
 265
 266             next_token_value = value
 267             while recorder.determine_route(next_token_value) is None:
 268                 if not proxy.can_advance(counter):
 269                     force = True
 270                     break
 271
 272                 next_token_type, next_token_value, *_ = proxy.eat(counter)
 273                 if next_token_type in (tokenize.COMMENT, tokenize.NL):
 274                     counter += 1
 275                     continue
 276
 277                 if next_token_type == tokenize.OP:
 278                     next_token_type = grammar.opmap[next_token_value]
 279
 280                 recorder.add_token(next_token_type, next_token_value)
 281                 counter += 1
 282
 283             ilabel = cast(int, recorder.determine_route(next_token_value, force=force))
 284             assert ilabel is not None
 285
 286         return self._addtoken(ilabel, type, value, context)
 287
 288     def _addtoken(self, ilabel: int, type: int, value: str, context: Context) -> bool:
 289         # Loop until the token is shifted; may raise exceptions
 290         while True:
 291             dfa, state, node = self.stack[-1]
 292             states, first = dfa
 293             arcs = states[state]
 294             # Look for a state with this label
 295             for i, newstate in arcs:
 296                 t = self.grammar.labels[i][0]
 297                 if t >= 256:
 298                     # See if it's a symbol and if we're in its first set
 299                     itsdfa = self.grammar.dfas[t]
 300                     itsstates, itsfirst = itsdfa
 301                     if ilabel in itsfirst:
 302                         # Push a symbol
 303                         self.push(t, itsdfa, newstate, context)
 304                         break  # To continue the outer while loop
 305
 306                 elif ilabel == i:
 307                     # Look it up in the list of labels
 308                     # Shift a token; we're done with it
 309                     self.shift(type, value, newstate, context)
 310                     # Pop while we are in an accept-only state
 311                     state = newstate
 312                     while states[state] == [(0, state)]:
 313                         self.pop()
 314                         if not self.stack:
 315                             # Done parsing!
 316                             return True
 317                         dfa, state, node = self.stack[-1]
 318                         states, first = dfa
 319                     # Done with this token
 320                     return False
 321
 322             else:
 323                 if (0, state) in arcs:
 324                     # An accepting state, pop it and try something else
 325                     self.pop()
 326                     if not self.stack:
 327                         # Done parsing, but another token is input
 328                         raise ParseError("too much input", type, value, context)
 329                 else:
 330                     # No success finding a transition
 331                     raise ParseError("bad input", type, value, context)
 332
 333     def classify(self, type: int, value: str, context: Context) -> List[int]:
 334         """Turn a token into a label.  (Internal)
 335
 336         Depending on whether the value is a soft-keyword or not,
 337         this function may return multiple labels to choose from."""
 338         if type == token.NAME:
 339             # Keep a listing of all used names
 340             self.used_names.add(value)
 341             # Check for reserved words
 342             if value in self.grammar.keywords:
 343                 return [self.grammar.keywords[value]]
 344             elif value in self.grammar.soft_keywords:
 345                 assert type in self.grammar.tokens
 346                 return [
 347                     self.grammar.soft_keywords[value],
 348                     self.grammar.tokens[type],
 349                 ]
 350
 351         ilabel = self.grammar.tokens.get(type)
 352         if ilabel is None:
 353             raise ParseError("bad token", type, value, context)
 354         return [ilabel]
 355
 356     def shift(self, type: int, value: str, newstate: int, context: Context) -> None:
 357         """Shift a token.  (Internal)"""
 358         if self.is_backtracking:
 359             dfa, state, _ = self.stack[-1]
 360             self.stack[-1] = (dfa, newstate, DUMMY_NODE)
 361         else:
 362             dfa, state, node = self.stack[-1]
 363             rawnode: RawNode = (type, value, context, None)
 364             newnode = convert(self.grammar, rawnode)
 365             assert node[-1] is not None
 366             node[-1].append(newnode)
 367             self.stack[-1] = (dfa, newstate, node)
 368
 369     def push(self, type: int, newdfa: DFAS, newstate: int, context: Context) -> None:
 370         """Push a nonterminal.  (Internal)"""
 371         if self.is_backtracking:
 372             dfa, state, _ = self.stack[-1]
 373             self.stack[-1] = (dfa, newstate, DUMMY_NODE)
 374             self.stack.append((newdfa, 0, DUMMY_NODE))
 375         else:
 376             dfa, state, node = self.stack[-1]
 377             newnode: RawNode = (type, None, context, [])
 378             self.stack[-1] = (dfa, newstate, node)
 379             self.stack.append((newdfa, 0, newnode))
 380
 381     def pop(self) -> None:
 382         """Pop a nonterminal.  (Internal)"""
 383         if self.is_backtracking:
 384             self.stack.pop()
 385         else:
 386             popdfa, popstate, popnode = self.stack.pop()
 387             newnode = convert(self.grammar, popnode)
 388             if self.stack:
 389                 dfa, state, node = self.stack[-1]
 390                 assert node[-1] is not None
 391                 node[-1].append(newnode)
 392             else:
 393                 self.rootnode = newnode
 394                 self.rootnode.used_names = self.used_names