parse.py 117 KB
Newer Older
1
# parse.py - parser combinators for DHParser
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
#
# Copyright 2016  by Eckhart Arnold (arnold@badw.de)
#                 Bavarian Academy of Sciences an Humanities (badw.de)
#
# 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
#
#     http://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.
Eckhart Arnold's avatar
Eckhart Arnold committed
17

18
19

"""
20
Module ``parse`` contains the python classes and functions for
21
22
DHParser's packrat-parser. It's central class is the
``Grammar``-class, which is the base class for any concrete
23
24
25
26
27
28
29
30
31
Grammar. Grammar-objects are callable and parsing is done by
calling a Grammar-object with a source text as argument.

The different parsing functions are callable descendants of class
``Parser``. Usually, they are organized in a tree and defined
within the namespace of a grammar-class. See ``ebnf.EBNFGrammar``
for an example.
"""

32

33
from collections import defaultdict
34
import copy
35
from typing import Callable, cast, List, Tuple, Set, Container, Dict, \
36
    DefaultDict, Union, Optional, Any
37

eckhart's avatar
eckhart committed
38
from DHParser.configuration import get_config_value
39
from DHParser.error import Error, linebreaks, line_col
40
from DHParser.log import HistoryRecord
41
from DHParser.preprocess import BEGIN_TOKEN, END_TOKEN, RX_TOKEN_NAME
42
from DHParser.stringview import StringView, EMPTY_STRING_VIEW
43
44
from DHParser.syntaxtree import Node, FrozenNode, RootNode, WHITESPACE_PTYPE, \
    TOKEN_PTYPE, ZOMBIE_TAG, ResultType
45
from DHParser.toolkit import sane_parser_name, escape_control_characters, re, cython, \
46
    RX_NEVER_MATCH, RxPatternType
47

48

49
__all__ = ('Parser',
50
           'UnknownParserError',
51
52
           'GrammarErrorType',
           'GrammarError',
53
           'Grammar',
Eckhart Arnold's avatar
Eckhart Arnold committed
54
           'EMPTY_NODE',
55
           'PreprocessorToken',
56
           'Token',
57
           'DropToken',
58
           'RegExp',
59
60
           'RE',
           'TKN',
61
           'Whitespace',
62
           'DropRegExp',
63
           'mixin_comment',
Eckhart Arnold's avatar
Eckhart Arnold committed
64
           'mixin_noempty',
65
           'MetaParser',
eckhart's avatar
eckhart committed
66
67
           'UnaryParser',
           'NaryParser',
68
           'Drop',
69
70
71
72
73
74
75
76
77
           'Synonym',
           'Option',
           'ZeroOrMore',
           'OneOrMore',
           'Series',
           'Alternative',
           'AllOf',
           'SomeOf',
           'Unordered',
eckhart's avatar
eckhart committed
78
           'Required',
79
80
81
82
83
84
85
86
87
88
           'Lookahead',
           'NegativeLookahead',
           'Lookbehind',
           'NegativeLookbehind',
           'last_value',
           'counterpart',
           'accumulate',
           'Capture',
           'Retrieve',
           'Pop',
89
           'Forward')
90
91
92
93


########################################################################
#
94
# Parser base class
95
96
97
98
#
########################################################################


99
EMPTY_NODE = FrozenNode(':EMPTY__', '')
100
101


Eckhart Arnold's avatar
Eckhart Arnold committed
102
103
104
class ParserError(Exception):
    """
    A `ParserError` is thrown for those parser errors that allow the
105
    controlled re-entrance of the parsing process after the error occurred.
Eckhart Arnold's avatar
Eckhart Arnold committed
106
    If a reentry-rule has been configured for the parser where the error
107
    occurred, the parser guard can resume the parsing process.
Eckhart Arnold's avatar
Eckhart Arnold committed
108
109
110
111
112

    Currently, the only case when a `ParserError` is thrown (and not some
    different kind of error like `UnknownParserError`, is when a `Series`-
    detects a missing mandatory element.
    """
113
114
115
116
    def __init__(self, node: Node, rest: StringView, error: Optional[Error], first_throw: bool):
        self.node = node   # type: Node
        self.rest = rest   # type: StringView
        self.error = error # type: Optional[Error]
117
        self.first_throw = first_throw  # type: bool
Eckhart Arnold's avatar
Eckhart Arnold committed
118

119
    def __str__(self):
120
        return "%i: %s    %s" % (self.node.pos, str(self.rest[:25]), repr(self.node))
121

Eckhart Arnold's avatar
Eckhart Arnold committed
122

123
ResumeList = List[RxPatternType]  # list of regular expressiones
Eckhart Arnold's avatar
Eckhart Arnold committed
124
125


eckhart's avatar
eckhart committed
126
@cython.locals(upper_limit=cython.int, closest_match=cython.int, pos=cython.int)
127
128
129
def reentry_point(rest: StringView,
                  rules: ResumeList,
                  comment_regex,
130
                  search_window: int = -1) -> int:
Eckhart Arnold's avatar
Eckhart Arnold committed
131
132
    """
    Finds the point where parsing should resume after a ParserError has been caught.
133
    The algorithm makes sure that this reentry-point does not lie inside a comment.
134
135
136
    The re-entry point is always the point after the end of the match of the regular
    expression defining the re-entry point. (Use look ahead, if you wand to define
    the re-entry point by what follows rather than by what text precedes the point.)
Eckhart Arnold's avatar
Eckhart Arnold committed
137
138
    Args:
        rest:  The rest of the parsed text or, in other words, the point where
139
140
141
142
            a ParserError was thrown.
        rules: A list of regular expressions. The rest of the text is searched for
            each of these. The closest match is the point where parsing will be
            resumed.
143
        comment_regex: A regular expression object that matches comments.
144
145
        search_window: The maximum size of the search window for finding the
            reentry-point. A value smaller or equal zero means that
Eckhart Arnold's avatar
Eckhart Arnold committed
146
    Returns:
147
148
        The integer index of the closest reentry point or -1 if no reentry-point
        was found.
Eckhart Arnold's avatar
Eckhart Arnold committed
149
    """
150
    upper_limit = len(rest) + 1
151
    closest_match = upper_limit
152
153
    comments = None  # typ: Optional[Iterator]

eckhart's avatar
eckhart committed
154
    @cython.locals(a=cython.int, b=cython.int)
155
156
157
158
159
160
161
162
163
164
165
    def next_comment() -> Tuple[int, int]:
        nonlocal rest, comments
        if comments:
            try:
                m = next(comments)
                a, b = m.span()
                return rest.index(a), rest.index(b)
            except StopIteration:
                comments = None
        return -1, -2

166
167
    # def str_search(s, start: int = 0) -> Tuple[int, int]:
    #     nonlocal rest
168
    #     return rest.find(s, start, start + search_window), len(s)
169

eckhart's avatar
eckhart committed
170
    @cython.locals(start=cython.int, end=cython.int)
171
172
    def rx_search(rx, start: int = 0) -> Tuple[int, int]:
        nonlocal rest
173
        m = rest.search(rx, start, start + search_window)
174
        if m:
175
176
            begin, end = m.span()
            return rest.index(begin), end - begin
177
178
        return -1, 0

eckhart's avatar
eckhart committed
179
    @cython.locals(a=cython.int, b=cython.int, k=cython.int, length=cython.int)
180
181
182
183
184
    def entry_point(search_func, search_rule) -> int:
        a, b = next_comment()
        k, length = search_func(search_rule)
        while a < b <= k:
            a, b = next_comment()
185
186
187
        # find next as long as start or end point of resume regex are inside a comment
        while (a < k < b) or (a < k + length < b):
            k, length = search_func(search_rule, b)
188
189
            while a < b <= k:
                a, b = next_comment()
190
        return k + length if k >= 0 else upper_limit
191

192
    # find closest match
Eckhart Arnold's avatar
Eckhart Arnold committed
193
    for rule in rules:
194
        comments = rest.finditer(comment_regex)
195
196
197
        assert not isinstance(rule, str), \
            'Strings not allowed as search rules, use a regular expression instead.'
        pos = entry_point(rx_search, rule)
198
        closest_match = min(pos, closest_match)
199

200
    # in case no rule matched return -1
201
202
203
    if closest_match == upper_limit:
        closest_match = -1
    return closest_match
Eckhart Arnold's avatar
Eckhart Arnold committed
204
205


eckhart's avatar
eckhart committed
206
207
208
209
ApplyFunc = Callable[['Parser'], None]
FlagFunc = Callable[[ApplyFunc, Set[ApplyFunc]], bool]


210
211
212
213
def copy_parser_attrs(src: 'Parser', duplicate: 'Parser'):
    """Duplicates all parser attributes from source to dest."""
    duplicate.pname = src.pname
    duplicate.anonymous = src.anonymous
Eckhart Arnold's avatar
Eckhart Arnold committed
214
    duplicate.drop_content = src.drop_content
215
216
217
    duplicate.tag_name = src.tag_name


218
class Parser:
219
220
221
222
223
224
225
226
227
228
229
230
231
232
    """
    (Abstract) Base class for Parser combinator parsers. Any parser
    object that is actually used for parsing (i.e. no mock parsers)
    should should be derived from this class.

    Since parsers can contain other parsers (see classes UnaryOperator
    and NaryOperator) they form a cyclical directed graph. A root
    parser is a parser from which all other parsers can be reached.
    Usually, there is one root parser which serves as the starting
    point of the parsing process. When speaking of "the root parser"
    it is this root parser object that is meant.

    There are two different types of parsers:

di68kap's avatar
di68kap committed
233
    1. *Named parsers* for which a name is set in field `parser.pname`.
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
       The results produced by these parsers can later be retrieved in
       the AST by the parser name.

    2. *Anonymous parsers* where the name-field just contains the empty
       string. AST-transformation of Anonymous parsers can be hooked
       only to their class name, and not to the individual parser.

    Parser objects are callable and parsing is done by calling a parser
    object with the text to parse.

    If the parser matches it returns a tuple consisting of a node
    representing the root of the concrete syntax tree resulting from the
    match as well as the substring `text[i:]` where i is the length of
    matched text (which can be zero in the case of parsers like
    `ZeroOrMore` or `Option`). If `i > 0` then the parser has "moved
    forward".

    If the parser does not match it returns `(None, text). **Note** that
    this is not the same as an empty match `("", text)`. Any empty match
    can for example be returned by the `ZeroOrMore`-parser in case the
    contained parser is repeated zero times.

    Attributes and Properties:
257
258
259
260
261
262
263
        pname:  The parser's name or a (possibly empty) alias name in case
                of an anonymous parser.
        anonymous: A property indicating that the parser remains anynomous
                anonymous with respect to the nodes it returns. For performance
                reasons this is implemented as an object variable rather
                than a property. This property must always be equal to
                `self.tag_name[0] == ":"`.
264
265
266
267
        drop_content: A property (for performance reasons implemented as
                simple field) that, if set, induces the parser not to return
                the parsed content or sub-tree if it has matched but the
                dummy `EMPTY_NODE`. In effect the parsed content will be
268
269
270
                dropped from the concrete syntax tree already. Only
                anonymous (or pseudo-anonymous) parsers are allowed to
                drop content.
271
        tag_name: The tag_name for the nodes that are created by
272
273
                the parser. If the parser is named, this is the same as
                `pname`, otherwise it is the name of the parser's type.
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
        visited:  Mapping of places this parser has already been to
                during the current parsing process onto the results the
                parser returned at the respective place. This dictionary
                is used to implement memoizing.

        recursion_counter:  Mapping of places to how often the parser
                has already been called recursively at this place. This
                is needed to implement left recursion. The number of
                calls becomes irrelevant once a resault has been memoized.

        cycle_detection:  The apply()-method uses this variable to make
                sure that one and the same function will not be applied
                (recursively) a second time, if it has already been
                applied to this parser.

289
        _grammar:  A reference to the Grammar object to which the parser
290
291
292
                is attached.
    """

293
    def __init__(self) -> None:
294
        # assert isinstance(name, str), str(name)
295
        self.pname = ''               # type: str
296
        self.anonymous = True         # type: bool
297
        self.drop_content = False     # type: bool
298
299
        self.tag_name = self.ptype    # type: str
        self.cycle_detection = set()  # type: Set[ApplyFunc]
300
301
302
303
        try:
            self._grammar = GRAMMAR_PLACEHOLDER  # type: Grammar
        except NameError:
            pass
304
305
306
        self.reset()

    def __deepcopy__(self, memo):
307
        """        Deepcopy method of the parser. Upon instantiation of a Grammar-
308
309
310
311
312
        object, parsers will be deep-copied to the Grammar object. If a
        derived parser-class changes the signature of the constructor,
        `__deepcopy__`-method must be replaced (i.e. overridden without
        calling the same method from the superclass) by the derived class.
        """
313
        duplicate = self.__class__()
314
        copy_parser_attrs(self, duplicate)
315
        return duplicate
316

317
    def __repr__(self):
di68kap's avatar
di68kap committed
318
        return self.pname + self.ptype
319
320

    def __str__(self):
di68kap's avatar
di68kap committed
321
        return self.pname + (' = ' if self.pname else '') + repr(self)
322

323
324
325
326
327
328
    @property
    def ptype(self) -> str:
        """Returns a type name for the parser. By default this is the name of
        the parser class with an added leading colon ':'. """
        return ':' + self.__class__.__name__

329
330
331
    @property
    def repr(self) -> str:
        """Returns the parser's name if it has a name and self.__repr___() otherwise."""
di68kap's avatar
di68kap committed
332
        return self.pname if self.pname else self.__repr__()
333

334
335
336
337
    def reset(self):
        """Initializes or resets any parser variables. If overwritten,
        the `reset()`-method of the parent class must be called from the
        `reset()`-method of the derived class."""
338
        self.visited = dict()  # type: Dict[int, Tuple[Optional[Node], StringView]]
eckhart's avatar
eckhart committed
339
        self.recursion_counter = defaultdict(int)  # type: DefaultDict[int, int]
340

341
342
343
    def _add_resume_notice(self, rest: StringView, err_node: Node) -> None:
        """Adds a resume notice to the error node with information about
        the reentry point and the parser."""
di68kap's avatar
di68kap committed
344
        if not self._grammar.resume_notices__ or self == self._grammar.start_parser__:
345
            return
346
        call_stack = self._grammar.call_stack__
347
        if len(call_stack) >= 2:
348
349
350
            i, N = -2, -len(call_stack)
            while i >= N and call_stack[i][0][0:1] in (':', '/', '"', "'", "`"):
                i -= 1
351
352
            if i >= N and i != -2:
                parent_info = "{}->{}".format(call_stack[i][0], call_stack[-2][0])
353
            else:
354
                parent_info = call_stack[-2][0]
355
356
        else:
            parent_info = "?"
di68kap's avatar
di68kap committed
357
358
        notice = Error('Resuming from parser {} with parser {} at point: {}'
                       .format(self.pname or self.ptype, parent_info, repr(rest[:10])),
359
                       self._grammar.document_length__ - len(rest), Error.RESUME_NOTICE)
360
        self._grammar.tree__.add_error(err_node, notice)
361

eckhart's avatar
eckhart committed
362
    @cython.locals(location=cython.int, gap=cython.int, i=cython.int)
363
364
365
    def __call__(self: 'Parser', text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given text. This is a wrapper method that adds
        the business intelligence that is common to all parsers. The actual parsing is
366
367
        done in the overridden method `_parse()`. This wrapper-method can be thought of
        as a "parser guard", because it guards the parsing process.
368
        """
369
370
371
372
373
374
375
376
377
        def get_error_node_id(error_node: Node, root_node: RootNode) -> int:
            if error_node:
                error_node_id = id(error_node)
                while error_node_id not in grammar.tree__.error_nodes and error_node.children:
                    error_node = error_node.result[-1]
                    error_node_id = id(error_node)
            else:
                error_node_id = 0

378
        grammar = self._grammar
di68kap's avatar
di68kap committed
379
        location = grammar.document_length__ - text._len  # faster then len(text)?
380
381

        try:
382
383
            # rollback variable changing operation if parser backtracks
            # to a position before the variable changing operation occurred
384
385
386
            if grammar.last_rb__loc__ >= location:
                grammar.rollback_to__(location)

387
            # if location has already been visited by the current parser, return saved result
388
389
            visited = self.visited  # using local variable for better performance
            if location in visited:
390
                # no history recording in case of memoized results
391
                return visited[location]
392
393

            # break left recursion at the maximum allowed depth
394
395
396
            left_recursion_depth__ = grammar.left_recursion_depth__
            if left_recursion_depth__:
                if self.recursion_counter[location] > left_recursion_depth__:
397
398
399
400
                    grammar.recursion_locations__.add(location)
                    return None, text
                self.recursion_counter[location] += 1

401
            # write current step to call stack, if history tracking is configured
402
403
            history_tracking__ = grammar.history_tracking__
            if history_tracking__:
di68kap's avatar
di68kap committed
404
                grammar.call_stack__.append(
405
                    ((self.repr if self.tag_name in (':RegExp', ':Token', ':DropToken')
406
                      else (self.pname or self.tag_name)), location))
407
                grammar.moving_forward__ = True
408
                error = None
409

410
            # finally, the actual parser call!
411
412
            try:
                node, rest = self._parse(text)
413
            except ParserError as pe:
414
                # catching up with parsing after an error occurred
415
                gap = len(text) - len(pe.rest)
di68kap's avatar
di68kap committed
416
                rules = grammar.resume_rules__.get(self.pname, [])
417
                rest = pe.rest[len(pe.node):]
418
419
                i = reentry_point(rest, rules, grammar.comment_rx__,
                                  grammar.reentry_search_window__)
420
                if i >= 0 or self == grammar.start_parser__:
421
                    assert pe.node.children or (not pe.node.result)
422
                    # apply reentry-rule or catch error at root-parser
di68kap's avatar
di68kap committed
423
424
                    # if i < 0:
                    #     i = 1
425
426
                    try:
                        zombie = pe.node[ZOMBIE_TAG]
427
                    except (KeyError, ValueError):
428
429
430
431
432
433
434
435
                        zombie = None
                    if zombie and not zombie.result:
                        zombie.result = rest[:i]
                        tail = tuple()
                    else:
                        nd = Node(ZOMBIE_TAG, rest[:i]).with_pos(location)
                        nd.attr['err'] = pe.error.message
                        tail = (nd,)
436
                    rest = rest[i:]
437
438
                    if pe.first_throw:
                        node = pe.node
439
                        node.result = node.children + tail
440
                    else:
441
442
                        node = Node(
                            self.tag_name,
di68kap's avatar
di68kap committed
443
444
445
                            (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) + tail) \
                            .with_pos(location)
                    self._add_resume_notice(rest, node)
446
                elif pe.first_throw:
447
                    if history_tracking__:  grammar.call_stack__.pop()
448
                    raise ParserError(pe.node, pe.rest, pe.error, first_throw=False)
449
                elif grammar.tree__.errors[-1].code == Error.MANDATORY_CONTINUATION_AT_EOF:
450
                    node = Node(self.tag_name, pe.node).with_pos(location)  # try to create tree as faithful as possible
451
                else:
452
453
                    result = (Node(ZOMBIE_TAG, text[:gap]).with_pos(location), pe.node) if gap \
                        else pe.node  # type: ResultType
454
                    if history_tracking__:  grammar.call_stack__.pop()
455
456
                    raise ParserError(Node(self.tag_name, result).with_pos(location),
                                      text, pe.error, first_throw=False)
457
458
                error = pe.error  # needed for history tracking

459
            if left_recursion_depth__:
460
461
462
463
464
465
                self.recursion_counter[location] -= 1
                # don't clear recursion_locations__ !!!

            if node is None:
                # retrieve an earlier match result (from left recursion) if it exists
                if location in grammar.recursion_locations__:
466
467
                    if location in visited:
                        node, rest = visited[location]
468
                        if location != grammar.last_recursion_location__:
469
470
471
                            grammar.tree__.add_error(
                                node, Error("Left recursion encountered. "
                                            "Refactor grammar to avoid slow parsing.",
472
473
                                            node.pos if node else location,
                                            Error.LEFT_RECURSION_WARNING))
474
                            error_id = id(node)
475
                            grammar.last_recursion_location__ = location
476
477
478
479
                    # don't overwrite any positive match (i.e. node not None) in the cache
                    # and don't add empty entries for parsers returning from left recursive calls!
                elif grammar.memoization__:
                    # otherwise also cache None-results
480
                    visited[location] = (None, rest)
481
            else:
482
                # assert node._pos < 0 or node == EMPTY_NODE
483
                # if node._pos != EMPTY_NODE:
484
                node._pos = location
485
486
                # assert node._pos >= 0 or node == EMPTY_NODE, \
                #     str("%i < %i" % (grammar.document_length__, location))
487
488
489
490
491
492
493
                if (grammar.last_rb__loc__ < location
                        and (grammar.memoization__ or location in grammar.recursion_locations__)):
                    # - variable manipulating parsers will not be entered into the cache,
                    #   because caching would interfere with changes of variable state
                    # - in case of left recursion, the first recursive step that
                    #   matches will store its result in the cache
                    # TODO: need a unit-test concerning interference of variable manipulation and left recursion algorithm?
494
                    visited[location] = (node, rest)
495
496
497

            # Mind that memoized parser calls will not appear in the history record!
            # Does this make sense? Or should it be changed?
498
            if history_tracking__:
499
500
                # don't track returning parsers except in case an error has occurred
                # remaining = len(rest)
501
                if grammar.moving_forward__:
502
                    record = HistoryRecord(grammar.call_stack__, node, text,
di68kap's avatar
di68kap committed
503
                                           grammar.line_col__(text))
504
                    grammar.history__.append(record)
505
506
507
508
                elif error:
                    # error_nid = id(node)  # type: int
                    # if error_nid in grammar.tree__.error_nodes:
                    record = HistoryRecord(grammar.call_stack__, node, text,
di68kap's avatar
di68kap committed
509
                                           grammar.line_col__(text),
510
511
                                           [error])
                    grammar.history__.append(record)
512
513
514
515
                grammar.moving_forward__ = False
                grammar.call_stack__.pop()

        except RecursionError:
516
            node = Node(ZOMBIE_TAG, str(text[:min(10, max(1, text.find("\n")))]) + " ...")
517
518
519
520
521
522
            node._pos = location
            grammar.tree__.new_error(node, "maximum recursion depth of parser reached; "
                                           "potentially due to too many errors!")
            rest = EMPTY_STRING_VIEW

        return node, rest
523
524
525
526
527
528
529
530
531
532
533
534

    def __add__(self, other: 'Parser') -> 'Series':
        """The + operator generates a series-parser that applies two
        parsers in sequence."""
        return Series(self, other)

    def __or__(self, other: 'Parser') -> 'Alternative':
        """The | operator generates an alternative parser that applies
        the first parser and, if that does not match, the second parser.
        """
        return Alternative(self, other)

eckhart's avatar
eckhart committed
535

536
537
538
539
540
541
    def _parse(self, text: StringView) -> Tuple[Optional[Node], StringView]:
        """Applies the parser to the given `text` and returns a node with
        the results or None as well as the text at the position right behind
        the matching string."""
        raise NotImplementedError

542
    @property
eckhart's avatar
eckhart committed
543
    def grammar(self) -> 'Grammar':
544
545
546
547
548
        try:
            if self._grammar != GRAMMAR_PLACEHOLDER:
                return self._grammar
            else:
                raise AssertionError('Grammar has not yet been set!')
549
550
        except (AttributeError, NameError):
            raise AttributeError('Parser placeholder does not have a grammar!')
551
552
553

    @grammar.setter
    def grammar(self, grammar: 'Grammar'):
554
555
556
557
558
559
560
561
562
        try:
            if self._grammar == GRAMMAR_PLACEHOLDER:
                self._grammar = grammar
                # self._grammar_assigned_notifier()
            elif self._grammar != grammar:
                  raise AssertionError("Parser has already been assigned"
                                       "to a different Grammar object!")
        except AttributeError:
            pass  # ignore setting of grammar attribute for placeholder parser
563
564
        except NameError:  # Cython: No access to GRAMMA_PLACEHOLDER, yet :-(
            self._grammar = grammar
565

eckhart's avatar
eckhart committed
566
    def _apply(self, func: ApplyFunc, flip: FlagFunc) -> bool:
567
568
        """
        Applies function `func(parser)` recursively to this parser and all
eckhart's avatar
eckhart committed
569
570
571
572
573
574
575
576
577
        descendant parsers, if any exist.

        In order to break cycles, function `flip` is called, which should
        return `True`, if this parser has already been visited. If not, it
        flips the cycle detection flag and returns `False`.

        This is a protected function and should not called from outside
        class Parser or any of its descendants. The entry point for external
        calls is the method `apply()` without underscore!
578
        """
eckhart's avatar
eckhart committed
579
        if flip(func, self.cycle_detection):
580
581
582
583
584
            return False
        else:
            func(self)
            return True

eckhart's avatar
eckhart committed
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
    def apply(self, func: ApplyFunc):
        """
        Applies function `func(parser)` recursively to this parser and all
        descendant parsers, if any exist. Traversal is pre-order.
        """
        def positive_flip(f: ApplyFunc, flagged: Set[Callable]) -> bool:
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == True`
            as meaning that `f` has already been applied."""
            if f in flagged:
                return True
            else:
                flagged.add(f)
                return False

        def negative_flip(f: ApplyFunc, flagged: Set[Callable]) -> bool:
            """Returns True, if function `f` has already been applied to this
            parser and sets the flag accordingly. Interprets `f in flagged == False`
            as meaning that `f` has already been applied."""
            if f not in flagged:
                return True
            else:
                flagged.remove(f)
                return False

        if func in self.cycle_detection:
            self._apply(func, negative_flip)
        else:
            self._apply(func, positive_flip)

615

eckhart's avatar
eckhart committed
616
617
def Drop(parser: Parser) -> Parser:
    """Returns the parser with the `parser.drop_content`-property set to `True`."""
Eckhart Arnold's avatar
Eckhart Arnold committed
618
    assert parser.anonymous, "Parser must be anonymous to be allowed to drop ist content."
eckhart's avatar
eckhart committed
619
620
621
    if isinstance(parser, Forward):
        cast(Forward, parser).parser.drop_content = True
    parser.drop_content = True
Eckhart Arnold's avatar
Eckhart Arnold committed
622
    return parser
eckhart's avatar
eckhart committed
623
624


625
PARSER_PLACEHOLDER = Parser()
626
627
628
629
630
631
632
633


########################################################################
#
# Grammar class, central administration of all parser of a grammar
#
########################################################################

634
635
def mixin_comment(whitespace: str, comment: str) -> str:
    """
636
    Returns a regular expression pattern that merges comment and whitespace
637
    regexps. Thus comments can occur wherever whitespace is allowed
638
639
640
641
642
643
    and will be skipped just as implicit whitespace.

    Note, that because this works on the level of regular expressions,
    nesting comments is not possible. It also makes it much harder to
    use directives inside comments (which isn't recommended, anyway).
    """
644
645
646
    if comment:
        return '(?:' + whitespace + '(?:' + comment + whitespace + ')*)'
    return whitespace
647
648


Eckhart Arnold's avatar
Eckhart Arnold committed
649
650
def mixin_noempty(whitespace: str) -> str:
    r"""
651
652
653
654
655
656
657
658
659
660
661
662
663
664
    Returns a regular expression pattern that matches only if the regular
    expression pattern `whitespace` matches AND if the match is not empty.

    If `whitespace` already matches the empty string '', then it will be
    returned unaltered.

    WARNING: `non_empty_ws` does not work regular expressions the matched
    strings of which can be followed by a symbol that can also occur at
    the start of the regular expression.

    In particular, it does not work for fixed size regular expressions,
    that ist / / or /   / or /\t/ won't work, but / */ or /\s*/ or /\s+/
    do work. There is no test for this. Fixed sizes regular expressions
    run through `non_empty_ws` will not match at any more if they are applied
Eckhart Arnold's avatar
Eckhart Arnold committed
665
666
667
668
669
    to the beginning or the middle of a sequence of whitespaces!

    In order to be safe, you whitespace regular expressions should follow
    the rule: "Whitespace cannot be followed by whitespace" or "Either
    grab it all or leave it all".
670
671
672
673
674
675
676
677
678
679

    :param whitespace: a regular expression pattern
    :return: new regular expression pattern that does not match the empty
        string '' any more.
    """
    if re.match(whitespace, ''):
        return r'(?:(?=(.|\n))' + whitespace + r'(?!\1))'
    return whitespace


680
class UnknownParserError(KeyError):
eckhart's avatar
eckhart committed
681
    """UnknownParserError is raised if a Grammar object is called with a
682
    parser that does not exist or if in the course of parsing a parser
eckhart's avatar
eckhart committed
683
    is referred to that does not exist."""
684
685


686
GrammarErrorType = Tuple[str, Parser, Error]      # TODO: replace with a named tuple?
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703


class GrammarError(Exception):
    """GrammarError will be raised if static analysis reveals errors
    in the grammar.
    """
    def __init__(self, static_analysis_result: List[GrammarErrorType]):
        assert static_analysis_result  # must not be empty
        self.errors = static_analysis_result

    def __str__(self):
        if len(self.errors) == 1:
            return str(self.errors[0][2])
        return '\n' + '\n'.join(("%i. " % (i + 1) + str(err_tuple[2]))
                                for i, err_tuple in enumerate(self.errors))


704
705
706
707
708
709
710
711
712
713
714
715
716
class Grammar:
    r"""
    Class Grammar directs the parsing process and stores global state
    information of the parsers, i.e. state information that is shared
    accross parsers.

    Grammars are basically collections of parser objects, which are
    connected to an instance object of class Grammar. There exist two
    ways of connecting parsers to grammar objects: Either by passing
    the root parser object to the constructor of a Grammar object
    ("direct instantiation"), or by assigning the root parser to the
    class variable "root__" of a descendant class of class Grammar.

eckhart's avatar
eckhart committed
717
    Example for direct instantiation of a grammar::
718

719
        >>> number = RE(r'\d+') + RE(r'\.') + RE(r'\d+') | RE(r'\d+')
720
721
722
723
724
725
726
727
728
729
730
731
732
733
        >>> number_parser = Grammar(number)
        >>> number_parser("3.1416").content
        '3.1416'

    Collecting the parsers that define a grammar in a descendant class of
    class Grammar and assigning the named parsers to class variables
    rather than global variables has several advantages:

    1. It keeps the namespace clean.

    2. The parser names of named parsers do not need to be passed to the
       constructor of the Parser object explicitly, but it suffices to
       assign them to class variables, which results in better
       readability of the Python code.
734
       See classmethod `Grammar._assign_parser_names__()`
735
736

    3. The parsers in the class do not necessarily need to be connected
737
738
       to one single root parser, which is helpful for testing and when
       building up a parser gradually from several components.
739
740
741
742
743
744
745

    As a consequence, though, it is highly recommended that a Grammar
    class should not define any other variables or methods with names
    that are legal parser names. A name ending with a double
    underscore '__' is *not* a legal parser name and can safely be
    used.

746
    Example::
747
748
749
750
751
752
753
754
755

        class Arithmetic(Grammar):
            # special fields for implicit whitespace and comment configuration
            COMMENT__ = r'#.*(?:\n|$)'  # Python style comments
            wspR__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)

            # parsers
            expression = Forward()
            INTEGER = RE('\\d+')
756
757
758
            factor = INTEGER | TKN("(") + expression + TKN(")")
            term = factor + ZeroOrMore((TKN("*") | TKN("/")) + factor)
            expression.set(term + ZeroOrMore((TKN("+") | TKN("-")) + term))
759
760
761
762
            root__ = expression

    Upon instantiation the parser objects are deep-copied to the
    Grammar object and assigned to object variables of the same name.
763
764
765
766
767
    For any parser that is directly assigned to a class variable the
    field `parser.pname` contains the variable name after instantiation
    of the Grammar class. The parser will never the less remain anonymous
    with respect to the tag names of the nodes it generates, if its name
    is matched by the `anonymous__` regular expression.
768
    If one and the same parser is assigned to several class variables
769
    such as, for example, the parser `expression` in the example above,
770
    which is also assigned to `root__`, the first name sticks.
771
772
773
774
775
776
777
778
779
780
781
782

    Grammar objects are callable. Calling a grammar object with a UTF-8
    encoded document, initiates the parsing of the document with the
    root parser. The return value is the concrete syntax tree. Grammar
    objects can be reused (i.e. called again) after parsing. Thus, it
    is not necessary to instantiate more than one Grammar object per
    thread.

    Grammar classes contain a few special class fields for implicit
    whitespace and comments that should be overwritten, if the defaults
    (no comments, horizontal right aligned whitespace) don't fit:

783
    Class Attributes:
784
785
786
787
        root__:  The root parser of the grammar. Theoretically, all parsers of the
                 grammar should be reachable by the root parser. However, for testing
                 of yet incomplete grammars class Grammar does not assume that this
                 is the case.
788

789
790
791
        resume_rules__: A mapping of parser names to a list of regular expressions
                that act as rules to find the reentry point if a ParserError was
                thrown during the execution of the parser with the respective name.
Eckhart Arnold's avatar
Eckhart Arnold committed
792

793
794
795
796
797
        anonymous__: A regular expression to identify names of parsers that are
                assigned to class fields but shall never the less yield anonymous
                nodes (i.e. nodes the tag name of which starts with a colon ":"
                followed by the parser's class name). The default is to treat all
                parsers starting with an underscore as anonymous in addition to those
798
799
                parsers that are not directly assigned to a class field.

eckhart's avatar
eckhart committed
800
        parser_initialization__:  Before the grammar class (!) has been initialized,
801
                 which happens upon the first time it is instantiated (see
802
                 `:func:_assign_parser_names()` for an explanation), this class
803
804
                 field contains a value other than "done". A value of "done" indicates
                 that the class has already been initialized.
805

806
807
808
809
810
811
812
        static_analysis_pending__: True as long as no static analysis (see the method
                with the same name for more information) has been done to check
                parser tree for correctness. Static analysis
                is done at instantiation and the flag is then set to false, but it
                can also be carried out once the class has been generated
                (by DHParser.ebnf.EBNFCompiler) and then be set to false in the
                definition of the grammar class already.
813

eckhart's avatar
eckhart committed
814
815
816
817
        python__src__:  For the purpose of debugging and inspection, this field can
                 take the python src of the concrete grammar class
                 (see `dsl.grammar_provider`).

818
    Instance Attributes:
819
820
        all_parsers__:  A set of all parsers connected to this grammar object

821
822
        comment_rx__:  The compiled regular expression for comments. If no
                comments have been defined, it defaults to RX_NEVER_MATCH
823
824
                This instance-attribute will only be defined if a class-attribute
                with the same name does not already exist!
825

eckhart's avatar
eckhart committed
826
827
828
829
        start_parser__:  During parsing, the parser with which the parsing process
                was started (see method `__call__`) or `None` if no parsing process
                is running.

830
831
832
833
834
835
836
        _dirty_flag__:  A flag indicating that the Grammar has been called at
                least once so that the parsing-variables need to be reset
                when it is called again.

        document__:  the text that has most recently been parsed or that is
                currently being parsed.

eckhart's avatar
eckhart committed
837
838
        document_length__:  the length of the document.

839
840
        document_lbreaks__ (property):  list of linebreaks within the document,
                starting with -1 and ending with EOF. This helps generating line
841
                and column number for history recording and will only be
842
                initialized if :attr:`history_tracking__` is true.
843

844
845
846
847
848
        tree__: The root-node of the parsing tree. This variable is available
               for error-reporting already during parsing  via
               ``self.grammar.tree__.add_error``, but it references the full
               parsing tree only after parsing has been finished.

849
        _reversed__:  the same text in reverse order - needed by the `Lookbehind`-
850
851
852
                parsers.

        variables__:  A mapping for variable names to a stack of their respective
853
854
                string values - needed by the :class:`Capture`-, :class:`Retrieve`-
                and :class:`Pop`-parsers.
855
856

        rollback__:  A list of tuples (location, rollback-function) that are
857
858
859
860
                deposited by the :class:`Capture`- and :class:`Pop`-parsers.
                If the parsing process reaches a dead end then all
                rollback-functions up to the point to which it retreats will be
                called and the state of the variable stack restored accordingly.
861
862
863

        last_rb__loc__:  The last, i.e. most advanced location in the text
                where a variable changing operation occurred. If the parser
864
865
                backtracks to a location at or before last_rb__loc__ (i.e.
                location <= last_rb__loc__) then a rollback of all variable
866
867
                changing operations is necessary that occurred after the
                location to which the parser backtracks. This is done by
868
                calling method :func:`rollback_to__(location)`.
869

di68kap's avatar
di68kap committed
870
871
872
        call_stack__:  A stack of the tag names and locations of all parsers
                in the call chain to the currently processed parser during
                parsing. The call stack can be thought of as a breadcrumb trail.
873
                This is required for recording the parser history (for debugging)
874
875
876
877
878
879
880
881
882
883
                and, eventually, i.e. one day in the future, for tracing through
                the parsing process.

        history__:  A list of parser-call-stacks. A parser-call-stack is
                appended to the list each time a parser either matches, fails
                or if a parser-error occurs.

        moving_forward__: This flag indicates that the parsing process is currently
                moving forward . It is needed to reduce noise in history recording
                and should not be considered as having a valid value if history
884
                recording is turned off! (See :func:`Parser.__call__`)
885
886
887
888

        recursion_locations__:  Stores the locations where left recursion was
                detected. Needed to provide minimal memoization for the left
                recursion detection algorithm, but, strictly speaking, superfluous
889
890
891
892
893
                if full memoization is enabled. (See :func:`Parser.__call__()`)

        last_recursion_location__:  Last location where left recursion was
                detected. This is used to avoid reduplicating warning messages
                about left recursion.
894
895
896
897
898
899

        memoization__:  Turns full memoization on or off. Turning memoization off
                results in less memory usage and sometimes reduced parsing time.
                In some situations it may drastically increase parsing time, so
                it is safer to leave it on. (Default: on)

900
901
902
903
        # Configuration parameters. These values of theses parameters are copied
                from the global configuration in the constructor of the Grammar
                object. (see mpodule `configuration.py`)

904
905
906
        flatten_tree__:  If True (default), anonymous nodes will be flattened
                during parsing already. This greatly reduces the concrete syntax
                tree and simplifies and speeds up abstract syntax tree generation.
907
                Default is on.
908
909
910

        left_recursion_depth__: the maximum allowed depth for left-recursion.
                A depth of zero means that no left recursion handling will
911
                take place. Default is 5.
912
913
914

        max_parser_dropouts__: Maximum allowed number of retries after errors
                where the parser would exit before the complete document has
915
916
                been parsed. Default is 1, as usually the retry-attemts lead
                to a proliferation of senseless error messages.
917
918
919

        reentry_search_window__: The number of following characters that the
                parser considers when searching a reentry point when a syntax error
920
921
922
923
924
925
926
927
928
                has been encountered. Default is 10.000 characters.

        history_tracking__:  A flag indicating that the parsing history shall
                be tracked. Default is off.

        resume_notices__: When resuming after an error a notice message is added
               in addition to the error message to report where, and, if history
               tracking is turned on, with which parser the parsing process
               will be resumed. Default is off.
929
    """
eckhart's avatar
eckhart committed
930
    python_src__ = ''  # type: str
931
    root__ = PARSER_PLACEHOLDER  # type: Parser
932
    # root__ must be overwritten with the root-parser by grammar subclass
eckhart's avatar
eckhart committed
933
    parser_initialization__ = ["pending"]  # type: List[str]
eckhart's avatar
eckhart committed
934
    resume_rules__ = dict()  # type: Dict[str, ResumeList]
935
    anonymous__ = RX_NEVER_MATCH  # type: RxPatternType
936
    # some default values
eckhart's avatar
eckhart committed
937
938
    COMMENT__ = r''  # type: str  # r'#.*(?:\n|$)'
    WSP_RE__ = mixin_comment(whitespace=r'[\t ]*', comment=COMMENT__)  # type: str
939
    static_analysis_pending__ = [True]  # type: List[bool]
940
941
942
943
944


    @classmethod
    def _assign_parser_names__(cls):
        """
di68kap's avatar
di68kap committed
945
        Initializes the `parser.pname` fields of those
946
        Parser objects that are directly assigned to a class field with
947
        the field's name, e.g.::
948

949
950
            class Grammar(Grammar):
                ...
951
                symbol = RE(r'(?!\\d)\\w+')
952

di68kap's avatar
di68kap committed
953
        After the call of this method symbol.pname == "symbol" holds.
di68kap's avatar
di68kap committed
954
955
        Parser names starting or ending with a double underscore like
        ``root__`` will be ignored. See :func:`sane_parser_name()`
956
957
958
959
960
961
962
963
964
965

        This is done only once, upon the first instantiation of the
        grammar class!

        Attention: If there exists more than one reference to the same
        parser, only the first one will be chosen for python versions
        greater or equal 3.6.  For python version <= 3.5 an arbitrarily
        selected reference will be chosen. See PEP 520
        (www.python.org/dev/peps/pep-0520/) for an explanation of why.
        """
eckhart's avatar
eckhart committed
966
        if cls.parser_initialization__[0] != "done":
967
968
969
            cdict = cls.__dict__
            for entry, parser in cdict.items():
                if isinstance(parser, Parser) and sane_parser_name(entry):
970
                    anonymous = True if cls.anonymous__.match(entry) else False
971
                    assert anonymous or not parser.drop_content, entry
di68kap's avatar
di68kap committed
972
                    if isinstance(parser, Forward):
di68kap's avatar
di68kap committed
973
974
                        if not cast(Forward, parser).parser.pname:
                            cast(Forward, parser).parser.pname = entry
975
                            cast(Forward, parser).parser.anonymous = anonymous
976
                    else:
di68kap's avatar
di68kap committed
977
                        parser.pname = entry
978
                        parser.anonymous = anonymous
eckhart's avatar
eckhart committed
979
            cls.parser_initialization__[0] = "done"
980
981
982


    def __init__(self, root: Parser = None) -> None:
983
        self.all_parsers__ = set()             # type: Set[Parser]
984
        # add compiled regular expression for comments, if it does not already exist
eckhart's avatar
eckhart committed
985
986
987
988
989
        if not hasattr(self, 'comment_rx__') or self.comment_rx__ is None:
            if hasattr(self.__class__, 'COMMENT__') and self.__class__.COMMENT__:
                self.comment_rx__ = re.compile(self.__class__.COMMENT__)
            else:
                self.comment_rx__ = RX_NEVER_MATCH
990
        else:
eckhart's avatar
eckhart committed
991
992
993
            assert ((self.__class__.COMMENT__ and
                     self.__class__.COMMENT__ == self.comment_rx__.pattern)
                    or (not self.__class__.COMMENT__ and self.comment_rx__ == RX_NEVER_MATCH))
994
        self.start_parser__ = None             # type: Optional[Parser]
995
996
        self._dirty_flag__ = False             # type: bool
        self.memoization__ = True              # type: bool
997
        self.flatten_tree__ = get_config_value('flatten_tree')                    # type: bool
998
999
1000
        self.left_recursion_depth__ = get_config_value('left_recursion_depth')    # type: int
        self.max_parser_dropouts__ = get_config_value('max_parser_dropouts')      # type: int
        self.reentry_search_window__ = get_config_value('reentry_search_window')  # type: int