syntaxtree.py 53.9 KB
Newer Older
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
# syntaxtree.py - syntax tree classes for DHParser
#
# 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.
17
18
19


"""
20
21
Module ``syntaxtree`` defines the ``Node``-class for syntax trees as well
as an abstract base class for parser-objects. The latter is defined
eckhart's avatar
eckhart committed
22
here, because node-objects refer to parser-objects. All concrete
23
24
25
parser classes are defined in the ``parse`` module.
"""

26
from collections import OrderedDict
eckhart's avatar
eckhart committed
27
import copy
28
import json
29
import sys
30
31
from typing import Callable, cast, Iterator, Sequence, List, AbstractSet, Set, Union, Tuple, \
    Optional, Dict
32

33
34
from DHParser.configuration import SERIALIZATIONS, XML_SERIALIZATION, SXPRESSION_SERIALIZATION, \
    COMPACT_SERIALIZATION, JSON_SERIALIZATION
eckhart's avatar
eckhart committed
35
from DHParser.error import Error, ErrorCode, linebreaks, line_col
36
from DHParser.stringview import StringView
Eckhart Arnold's avatar
Eckhart Arnold committed
37
from DHParser.toolkit import get_config_value, re
di68kap's avatar
di68kap committed
38

39

di68kap's avatar
di68kap committed
40
__all__ = ('WHITESPACE_PTYPE',
41
           'TOKEN_PTYPE',
42
43
           'ZOMBIE_TAG',
           'PLACEHOLDER',
eckhart's avatar
eckhart committed
44
45
46
           'ResultType',
           'StrictResultType',
           'ChildrenType',
47
           'Node',
48
           'FrozenNode',
49
           'tree_sanity_check',
di68kap's avatar
di68kap committed
50
           'RootNode',
51
           'DHParser_JSONEncoder',
52
           'parse_sxpr',
53
           'parse_xml',
54
           'parse_json_syntaxtree',
eckhart's avatar
eckhart committed
55
           'parse_tree',
56
57
           'flatten_sxpr',
           'flatten_xml')
Eckhart Arnold's avatar
Eckhart Arnold committed
58
59


60
61
62
63
64
65
66
67
#######################################################################
#
# parser base and mock parsers
#
#######################################################################


WHITESPACE_PTYPE = ':Whitespace'
68
TOKEN_PTYPE = ':Token'
69

70
ZOMBIE_TAG = "__ZOMBIE__"
71

72
73
74
75
76
77
78
#######################################################################
#
# syntaxtree nodes
#
#######################################################################


eckhart's avatar
eckhart committed
79
80
RX_IS_SXPR = re.compile(r'\s*\(')
RX_IS_XML = re.compile(r'\s*<')
81
RX_ATTR_NAME = re.compile(r'[\w.:-]')
eckhart's avatar
eckhart committed
82
83


84
def flatten_sxpr(sxpr: str, threshold: int = -1) -> str:
85
86
    """
    Returns S-expression ``sxpr`` as a one-liner without unnecessary
Eckhart Arnold's avatar
Eckhart Arnold committed
87
88
    whitespace.

89
90
91
92
93
94
95
    The ``threshold`` value is a maximum number of
    characters allowed in the flattened expression. If this number
    is exceeded the the unflattened S-expression is returned. A
    negative number means that the S-expression will always be
    flattened. Zero or (any postive integer <= 3) essentially means
    that the expression will not be flattened.

Eckhart Arnold's avatar
Eckhart Arnold committed
96
    Example:
Eckhart Arnold's avatar
Eckhart Arnold committed
97
    >>> flatten_sxpr('(a\\n    (b\\n        c\\n    )\\n)\\n')
Eckhart Arnold's avatar
Eckhart Arnold committed
98
99
    '(a (b c))'
    """
eckhart's avatar
eckhart committed
100
101
102
    assert RX_IS_SXPR.match(sxpr)
    if threshold == 0:
        return sxpr
103
    flat = re.sub(r'\s(?=\))', '', re.sub(r'\s+', ' ', sxpr)).strip()
eckhart's avatar
eckhart committed
104
    if len(flat) > threshold >= 0:
105
106
        return sxpr.strip()
    return flat
Eckhart Arnold's avatar
Eckhart Arnold committed
107
108


109
def flatten_xml(xml: str) -> str:
110
111
    """
    Returns an XML-tree as a one liner without unnecessary whitespace,
112
    i.e. only whitespace within leaf-nodes is preserved.
113
114
    A more precise alternative to `flatten_xml` is to use Node.as_xml()
    ans passing a set containing the top level tag to parameter `inline_tags`.
115
    """
116
117
    # works only with regex
    # return re.sub(r'\s+(?=<\w)', '', re.sub(r'(?<=</\w+>)\s+', '', xml))
eckhart's avatar
eckhart committed
118
    assert RX_IS_XML.match(xml)
eckhart's avatar
eckhart committed
119

120
    def tag_only(m):
eckhart's avatar
eckhart committed
121
        """Return only the tag, drop the whitespace."""
122
        return m.groupdict()['closing_tag']
123
    return re.sub(r'\s+(?=<[\w:])', '', re.sub(r'(?P<closing_tag></:?\w+>)\s+', tag_only, xml))
124
125


126
127
128
129
130
ChildrenType = Tuple['Node', ...]
NoChildren = cast(ChildrenType, ())  # type: ChildrenType
StrictResultType = Union[ChildrenType, StringView, str]
ResultType = Union[ChildrenType, 'Node', StringView, str, None]

eckhart's avatar
eckhart committed
131
RX_AMP = re.compile(r'&(?!\w+;)')
132
133


Eckhart Arnold's avatar
Eckhart Arnold committed
134
class Node:  # (collections.abc.Sized): Base class omitted for cython-compatibility
135
136
137
    """
    Represents a node in the concrete or abstract syntax tree.

138
139
    TODO: Add some documentation and doc-tests here...

eckhart's avatar
eckhart committed
140
    Attributes and Properties:
141
142
        tag_name (str):  The name of the node, which is either its
            parser's name or, if that is empty, the parser's class name
143

144
145
146
        result (str or tuple):  The result of the parser which
            generated this node, which can be either a string or a
            tuple of child nodes.
147

148
149
        children (tuple):  The tuple of child nodes or an empty tuple
            if there are no child nodes. READ ONLY!
150

eckhart's avatar
eckhart committed
151
152
153
154
        content (str):  Yields the contents of the tree as string. The
            difference to ``str(node)`` is that ``node.content`` does
            not add the error messages to the returned string.

155
156
157
        len (int):  The full length of the node's string result if the
            node is a leaf node or, otherwise, the concatenated string
            result's of its descendants. The figure always represents
158
            the length before AST-transformation and will never change
159
            through AST-transformation. READ ONLY!
160

161
162
        pos (int):  the position of the node within the parsed text.

Eckhart Arnold's avatar
Eckhart Arnold committed
163
            The value of ``pos`` is -1 meaning invalid by default.
164
            Setting this value will set the positions of all child
Eckhart Arnold's avatar
Eckhart Arnold committed
165
            nodes relative to this value.
166
167

            To set the pos values of all nodes in a syntax tree, the
Eckhart Arnold's avatar
Eckhart Arnold committed
168
            pos value of the root node should be set to 0 right
169
170
            after parsing.

Eckhart Arnold's avatar
Eckhart Arnold committed
171
            Other than that, this value should be considered READ ONLY.
172
173
            At any rate, it should only be reassigned during the parsing
            stage and never during or after the AST-transformation.
174

175
176
        attr (dict): An optional dictionary of XML-attr. This
            dictionary is created lazily upon first usage. The attr
177
178
            will only be shown in the XML-Representation, not in the
            S-Expression-output.
179
    """
180

181
    __slots__ = '_result', 'children', '_pos', 'tag_name', '_xml_attr', '_id'
182

183
    def __init__(self, tag_name: str, result: ResultType, leafhint: bool = False) -> None:
184
185
        """
        Initializes the ``Node``-object with the ``Parser``-Instance
186
187
        that generated the node and the parser's result.
        """
eckhart's avatar
eckhart committed
188
        self._pos = -1                  # type: int
189
        # Assignment to self.result initializes the attr _result, children and _len
di68kap's avatar
di68kap committed
190
        # The following if-clause is merely an optimization, i.e. a fast-path for leaf-Nodes
191
        if leafhint:
eckhart's avatar
eckhart committed
192
            self._result = result       # type: StrictResultType  # cast(StrictResultType, result)
193
194
195
            self.children = NoChildren  # type: ChildrenType
        else:
            self.result = result
196
        self.tag_name = tag_name        # type: str
197

eckhart's avatar
eckhart committed
198
199
    def __deepcopy__(self, memo):
        if self.children:
200
            duplicate = self.__class__(self.tag_name, copy.deepcopy(self.children), False)
eckhart's avatar
eckhart committed
201
        else:
202
            duplicate = self.__class__(self.tag_name, self.result, True)
eckhart's avatar
eckhart committed
203
        duplicate._pos = self._pos
204
        if self.has_attr():
di68kap's avatar
di68kap committed
205
206
            duplicate.attr.update(copy.deepcopy(self._xml_attr))
            # duplicate._xml_attr = copy.deepcopy(self._xml_attr)  # this is not cython compatible
eckhart's avatar
eckhart committed
207
        return duplicate
Eckhart Arnold's avatar
Eckhart Arnold committed
208

209
    def __str__(self):
210
211
        if isinstance(self, RootNode):
            root = cast(RootNode, self)
212
            errors = root.errors_sorted
213
214
            if errors:
                e_pos = errors[0].pos
Eckhart Arnold's avatar
Eckhart Arnold committed
215
                content = self.content
eckhart's avatar
eckhart committed
216
217
                return content[:e_pos] + ' <<< Error on "%s" | %s >>> ' % \
                    (content[e_pos - self.pos:], '; '.join(e.message for e in errors))
218
        return self.content
Eckhart Arnold's avatar
Eckhart Arnold committed
219

220
    def __repr__(self):
221
        # mpargs = {'name': self.parser.name, 'ptype': self.parser.ptype}
222
223
        # name, ptype = (self._tag_name.split(':') + [''])[:2]
        # parg = "MockParser({name}, {ptype})".format(name=name, ptype=ptype)
224
        rarg = str(self) if not self.children else \
225
            "(" + ", ".join(child.__repr__() for child in self.children) + ")"
226
        return "Node(%s, %s)" % (self.tag_name, rarg)
227

228
    def __len__(self):
229
230
        return (sum(len(child) for child in self.children)
                if self.children else len(self._result))
231
232

    def __bool__(self):
233
234
235
236
        """Returns the bool value of a node, which is always True. The reason
        for this is that a boolean test on a variable that can contain a node
        or None will only yield `False` in case of None.
        """
237
238
        return True

239
    def __hash__(self):
240
        return hash(self.tag_name)
241

242
    def equals(self, other: 'Node') -> bool:
243
        """
244
245
246
247
248
249
        Equality of value: Two nodes are considered as having the same value,
        if their tag name is the same, if their results are equal and
        if their attributes and attribute values are the same.

        Returns True, if the tree originating in node `self` is equal by
        value to the tree originating in node `other`.
250
251
252
253
254
255
256
257
258
        """
        if self.tag_name == other.tag_name and self.compare_attr(other):
            if self.children:
                return (len(self.children) == len(other.children)
                        and all(a.equals(b) for a, b in zip(self.children, other.children)))
            else:
                return self.result == other.result
        return False

259
260
261
262
263
264
265
266
267
268
269
270
271
    def get(self, index_or_tagname: Union[int, str],
            surrogate: Union['Node', Iterator['Node']]) -> Union['Node', Iterator['Node']]:
        """Returns the child node with the given index if ``index_or_tagname``
        is an integer or the first child node with the given tag name. If no
        child with the given index or tag_name exists, the ``surrogate`` is
        returned instead. This mimics the behaviour of Python's dictionary's
        get-method.
        """
        try:
            return self[index_or_tagname]
        except KeyError:
            return surrogate

272
    def is_anonymous(self) -> bool:
eckhart's avatar
eckhart committed
273
274
275
276
277
278
279
280
        """Returns True, if the Node is an "anonymous" Node, i.e. a node that
        has not been created by a named parser.

        The tag name of anonymous node is a colon followed by the class name
        of the parser that created the node, i.e. ":Series". It is recommended
        practice to remove (or name) all anonymous nodes during the
        AST-transformation.
        """
Eckhart Arnold's avatar
Eckhart Arnold committed
281
        return not self.tag_name or self.tag_name[0] == ':'
282

283
    # node content ###
Eckhart Arnold's avatar
Eckhart Arnold committed
284

285
    @property
Eckhart Arnold's avatar
Eckhart Arnold committed
286
    def result(self) -> StrictResultType:
287
288
289
290
291
        """
        Returns the result from the parser that created the node.
        Error messages are not included in the result. Use `self.content()`
        if the result plus any error messages is needed.
        """
292
293
294
        return self._result

    @result.setter
Eckhart Arnold's avatar
Eckhart Arnold committed
295
    def result(self, result: ResultType):
Eckhart Arnold's avatar
Eckhart Arnold committed
296
        # # made obsolete by static type checking with mypy
eckhart's avatar
eckhart committed
297
298
299
300
        # assert ((isinstance(result, tuple) and all(isinstance(child, Node) for child in result))
        #         or isinstance(result, Node)
        #         or isinstance(result, str)
        #         or isinstance(result, StringView)), "%s (%s)" % (str(result), str(type(result)))
Eckhart Arnold's avatar
Eckhart Arnold committed
301
302
        # Possible optimization: Do not allow single nodes as argument:
        # assert not isinstance(result, Node)
303
        # self._content = None
304
305
306
307
308
309
310
311
312
        if isinstance(result, Node):
            self.children = (result,)
            self._result = self.children
        else:
            if isinstance(result, tuple):
                self.children = result
                self._result = result or ''
            else:
                self.children = NoChildren
eckhart's avatar
eckhart committed
313
                self._result = result  # cast(StrictResultType, result)
314

315
316
317
318
319
320
321
322
323
324
325
326
    def _content(self) -> List[str]:
        """
        Returns string content as list of string fragments
        that are gathered from all child nodes in order.
        """
        if self.children:
            fragments = []
            for child in self.children:
                fragments.extend(child._content())
            return fragments
        self._result = str(self._result)
        return [self._result]
327
328

    @property
eckhart's avatar
eckhart committed
329
    def content(self) -> str:
330
        """
331
332
333
        Returns content as string. If the node has child-nodes, the
        string content of the child-nodes is recursively read and then
        concatenated.
334
        """
335
336
337
338
339
340
341
342
        if self.children:
            fragments = []
            for child in self.children:
                fragments.extend(child._content())
            return ''.join(fragments)
        self._result = str(self._result)
        return self._result
        # unoptimized
Eckhart Arnold's avatar
Eckhart Arnold committed
343
344
        # return "".join(child.content for child in self.children) if self.children \
        #     else str(self._result)
di68kap's avatar
di68kap committed
345

346
    # node position ###
di68kap's avatar
di68kap committed
347

348
    @property
349
    def pos(self) -> int:
eckhart's avatar
eckhart committed
350
351
        """Returns the position of the Node's content in the source text."""
        if self._pos < 0:
Eckhart Arnold's avatar
Eckhart Arnold committed
352
            raise AssertionError("Position value not initialized! Use Node.with_pos()")
353
354
        return self._pos

Eckhart Arnold's avatar
Eckhart Arnold committed
355
    def with_pos(self, pos: int) -> 'Node':
eckhart's avatar
eckhart committed
356
        """
Eckhart Arnold's avatar
Eckhart Arnold committed
357
        Initialize position value. Usually, the parser guard
eckhart's avatar
eckhart committed
358
359
        (`parsers.add_parser_guard()`) takes care of assigning the
        position in the document to newly created nodes. However,
Eckhart Arnold's avatar
Eckhart Arnold committed
360
        when Nodes are created outside the reach of the parser
eckhart's avatar
eckhart committed
361
        guard, their document-position must be assigned manually.
Eckhart Arnold's avatar
Eckhart Arnold committed
362
363
        Position values of the child nodes are assigned recursively, too.
        Returns the node itself for convenience.
eckhart's avatar
eckhart committed
364
        """
365
366
367
368
        # condition self.pos == pos cannot be assumed when tokens or whitespace
        # are dropped early!
        # assert self._pos < 0 or self.pos == pos, ("pos mismatch %i != %i at Node: %s"
        #                                           % (self._pos, pos, repr(self)))
Eckhart Arnold's avatar
Eckhart Arnold committed
369
370
371
372
373
374
375
376
377
378
        if pos != self._pos >= 0:
            raise AssertionError("Position value cannot be reassigned to a different value!")
        if self._pos < 0:
            self._pos = pos
            # recursively adjust pos-values of all children
            offset = self.pos
            for child in self.children:
                if child._pos < 0:
                    child.with_pos(offset)
                offset = child.pos + len(child)
eckhart's avatar
eckhart committed
379
380
        return self

381
    # (XML-)attributes ###
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397

    def has_attr(self) -> bool:
        """
        Returns `True`, if the node has any attributes, `False` otherwise.

        This function does not create an attribute dictionary, therefore
        it should be preferred to querying node.attr when testing for the
        existence of any attributes.
        """
        try:
            # if self._xml_attr is not None:
            #     return True
            return bool(self._xml_attr)
        except AttributeError:
            pass
        return False
398

399
400
401
402
    @property
    def attr(self):
        """
        Returns a dictionary of XML-attr attached to the node.
403
404
405
406
407
408
409
410
411
412

        Examples:
            >>> node = Node(None, '')
            >>> print('Any attributes present?', node.has_attr())
            Any attributes present? False
            >>> node.attr['id'] = 'identificator'
            >>> node.attr
            OrderedDict([('id', 'identificator')])
            >>> node.attr['id']
            'identificator'
413
            >>> del node.attr['id']
414
415
416
417
418
419
420
            >>> node.attr
            OrderedDict()

        NOTE: Use `node.attr_active()` rather than bool(node.attr) to check the
        presence of any attributes. Attribute dictionaries are created lazily
        and node.attr would create a dictionary, even though it may never be
        needed any more.
421
422
423
424
425
426
427
428
429
        """
        try:
            if self._xml_attr is None:          # cython compatibility
                self._xml_attr = OrderedDict()
        except AttributeError:
            self._xml_attr = OrderedDict()
        return self._xml_attr

    def compare_attr(self, other: 'Node') -> bool:
430
        """
431
432
        Returns True, if `self` and `other` have the same attributes with the
        same attribute values.
433
        """
434
435
        if self.has_attr():
            if other.has_attr():
436
437
438
                return self.attr == other.attr
            return len(self.attr) == 0
            # self has empty dictionary and other has no attributes
439
        elif other.has_attr():
440
441
442
            return len(other.attr) == 0
            # other has empty attribute dictionary and self as no attributes
        return True  # neither self nor other have any attributes
443

444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
    # tree traversal and node selection ###

    def __getitem__(self, index_or_tagname: Union[int, str]) -> Union['Node', Iterator['Node']]:
        """
        Returns the child node with the given index if ``index_or_tagname`` is
        an integer or the first child node with the given tag name. Examples::

            >>> tree = parse_sxpr('(a (b "X") (X (c "d")) (e (X "F")))')
            >>> flatten_sxpr(tree[0].as_sxpr())
            '(b "X")'
            >>> flatten_sxpr(tree["X"].as_sxpr())
            '(X (c "d"))'

        Args:
            index_or_tagname(str): Either an index of a child node or a
                tag name.
        Returns:
            Node: All nodes which have a given tag name.
        """
        if self.children:
            if isinstance(index_or_tagname, int):
                return self.children[index_or_tagname]
            else:
                for child in self.children:
                    if child.tag_name == index_or_tagname:
                        return child
                raise KeyError(index_or_tagname)
        raise ValueError('Leave nodes have no children that can be indexed!')

    def __contains__(self, tag_name: str) -> bool:
        """
        Returns true if a child with the given tag name exists.
        Args:
            tag_name (str): tag_name which will be searched among to immediate
                descendants of this node.
        Returns:
            bool:  True, if at least one descendant node with the given tag
                name exists, False otherwise
        """
        # assert isinstance(tag_name, str)
        if self.children:
            for child in self.children:
                if child.tag_name == tag_name:
                    return True
            return False
        raise ValueError('Leave node cannot contain other nodes')

    def index(self, tag_name: str, start: int = 0, stop: int = sys.maxsize) -> int:
        """
        Returns the first index of the child with the tag name `what`. If the
        parameters start and stop are given, the search is restricted to the
        children with indices from the half-open interval [start:end[.
        If no such child exists a ValueError is raised.
        :param tag_name: the child's tag name for which the index shall be returned
        :param start: the first index to start searching.
        :param stop: the last index that shall be searched
        :return: the index of the first child with the given tag name.
        """
        assert 0 <= start <= stop
        i = start
        for child in self.children[start:stop]:
            if child.tag_name == tag_name:
                return i
            i += 1
Eckhart Arnold's avatar
Eckhart Arnold committed
508

509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
    def select(self, match_function: Callable, include_root: bool = False, reverse: bool = False) \
            -> Iterator['Node']:
        """
        Finds nodes in the tree that fulfill a given criterion.

        `select` is a generator that yields all nodes for which the
        given `match_function` evaluates to True. The tree is
        traversed pre-order.

        See function `Node.select_by_tag` for some examples.

        Args:
            match_function (function): A function  that takes as Node
                object as argument and returns True or False
            include_root (bool): If False, only descendant nodes will be
                checked for a match.
            reverse (bool): If True, the tree will be walked in reverse
                order, i.e. last children first.
        Yields:
            Node: All nodes of the tree for which
            ``match_function(node)`` returns True
        """
        if include_root and match_function(self):
            yield self
        child_iterator = reversed(self.children) if reverse else self.children
        for child in child_iterator:
            if match_function(child):
                yield child
            yield from child.select(match_function, False, reverse)
        # The above variant is slightly faster
        # for child in child_iterator:
        #     yield from child.select(match_function, True, reverse)

    def select_by_tag(self, tag_names: Union[str, AbstractSet[str]],
                      include_root: bool = False) -> Iterator['Node']:
        """
        Returns an iterator that runs through all descendants that have one
        of the given tag names.

        Examples::

            >>> tree = parse_sxpr('(a (b "X") (X (c "d")) (e (X "F")))')
            >>> list(flatten_sxpr(item.as_sxpr()) for item in tree.select_by_tag("X", False))
            ['(X (c "d"))', '(X "F")']
            >>> list(flatten_sxpr(item.as_sxpr()) for item in tree.select_by_tag({"X", "b"}, False))
            ['(b "X")', '(X (c "d"))', '(X "F")']
            >>> any(tree.select_by_tag('a', False))
            False
            >>> list(flatten_sxpr(item.as_sxpr()) for item in tree.select_by_tag('a', True))
            ['(a (b "X") (X (c "d")) (e (X "F")))']
            >>> flatten_sxpr(next(tree.select_by_tag("X", False)).as_sxpr())
            '(X (c "d"))'

        Args:
eckhart's avatar
eckhart committed
563
            tag_names(set): A tag name or set of tag names that is being
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
                searched for
            include_root (bool): If False, only descendant nodes will be
                checked for a match.
        Yields:
            Node: All nodes which have a given tag name.
        """
        if isinstance(tag_names, str):
            tag_names = frozenset({tag_names})
        return self.select(lambda node: node.tag_name in tag_names, include_root)

    def pick(self, tag_names: Union[str, Set[str]]) -> Optional['Node']:
        """
        Picks the first descendant with one of the given tag_names.

        This function is mostly just syntactic sugar for
        ``next(node.select_by_tag(tag_names, False))``. However, rather than
        raising a StopIterationError if no descendant with the given tag-name
        exists, it returns None.
        """
        try:
            return next(self.select_by_tag(tag_names, False))
        except StopIteration:
            return None

588
    # serialization ###
589

590
    def _tree_repr(self, tab, open_fn, close_fn, data_fn=lambda i: i,
591
                   density=0, inline=False, inline_fn=lambda node: False) -> str:
592
593
594
595
596
597
598
599
        """
        Generates a tree representation of this node and its children
        in string from.

        The kind ot tree-representation that is determined by several
        function parameters. This could be an XML-representation or a
        lisp-like S-expression.

600
        Args:
601
            tab (str):  The indentation string, e.g. '\t' or '    '
eckhart's avatar
eckhart committed
602
            open_fn:   (Node->str) A function that returns an opening
603
                string (e.g. an XML-tag_name) for a given node
eckhart's avatar
eckhart committed
604
            close_fn:  (Node->str) A function that returns a closeF
605
                string (e.g. an XML-tag_name) for a given node.
eckhart's avatar
eckhart committed
606
            data_fn:   (str->str) A function that filters the data string
607
608
609
610
611
612
                before printing, e.g. to add quotation marks

        Returns (str):
            A string that contains a (serialized) tree representation
            of the node and its children.
        """
eckhart's avatar
eckhart committed
613
614
        head = open_fn(self)
        tail = close_fn(self)
615
616

        if not self.result:
617
            return head.rstrip() + tail.lstrip()
618

eckhart's avatar
eckhart committed
619
        tail = tail.lstrip(None if density & 2 else '')
620

621
        inline = inline or inline_fn(self)
622
623
624
625
626
        if inline:
            head = head.rstrip()
            tail = tail.lstrip()
            usetab, sep = '', ''
        else:
eckhart's avatar
eckhart committed
627
628
            usetab = tab if head else ''    # no indentation if tag is already omitted
            sep = '\n'
629

630
631
        if self.children:
            content = []
632
            for child in self.children:
633
                subtree = child._tree_repr(tab, open_fn, close_fn, data_fn,
634
                                           density, inline, inline_fn)
eckhart's avatar
eckhart committed
635
                if subtree:
eckhart's avatar
eckhart committed
636
637
                    st = [subtree] if inline else subtree.split('\n')
                    content.append((sep + usetab).join(s for s in st))
638
            return head + usetab + (sep + usetab).join(content) + tail
639

eckhart's avatar
eckhart committed
640
        res = self.content
eckhart's avatar
eckhart committed
641
        if not inline and not head:
eckhart's avatar
eckhart committed
642
            # strip whitespace for omitted non inline node, e.g. CharData in mixed elements
eckhart's avatar
eckhart committed
643
            res = res.strip()
644
645
        if density & 1 and res.find('\n') < 0:  # and head[0] == "<":
            # except for XML, add a gap between opening statement and content
646
            gap = ' ' if not inline and head and head.rstrip()[-1:] != '>' else ''
eckhart's avatar
eckhart committed
647
            return head.rstrip() + gap + data_fn(res) + tail.lstrip()
648
        else:
649
            return head + '\n'.join([usetab + data_fn(s) for s in res.split('\n')]) + tail
650

651
    def as_sxpr(self, src: Optional[str] = None,
652
                indentation: int = 2,
653
                compact: bool = False,
eckhart's avatar
eckhart committed
654
                flatten_threshold: int = 92) -> str:
655
        """
656
        Returns content as S-expression, i.e. in lisp-like form. If this
eckhart's avatar
eckhart committed
657
        method is called on a RootNode-object,
658

659
        Args:
660
661
            src:  The source text or `None`. In case the source text is
                given the position of the element in the text will be
662
663
664
                reported as position, line, column. In case the empty string is
                given rather than None, only the position value will be
                reported in case it has been initialized, i.e. pos >= 0.
665
666
            indentation: The number of whitespaces for indentation
            compact:  If True, a compact representation is returned where
667
                brackets are omitted and only the indentation indicates the
Eckhart Arnold's avatar
Eckhart Arnold committed
668
                tree structure.
669
670
671
            flatten_threshold:  Return the S-expression in flattened form if
                the flattened expression does not exceed the threshold length.
                A negative number means that it will always be flattened.
672
673
        """

eckhart's avatar
eckhart committed
674
        left_bracket, right_bracket, density = ('', '', 1) if compact else ('(', '\n)', 0)
eckhart's avatar
eckhart committed
675
        lbreaks = linebreaks(src) if src else []  # type: List[int]
676
        root = cast(RootNode, self) if isinstance(self, RootNode) else None  # type: Optional[RootNode]
677

678
        def opening(node: Node) -> str:
eckhart's avatar
eckhart committed
679
            """Returns the opening string for the representation of `node`."""
eckhart's avatar
eckhart committed
680
            txt = [left_bracket, node.tag_name]
681
            # s += " '(pos %i)" % node.add_pos
Eckhart Arnold's avatar
Eckhart Arnold committed
682
            # txt.append(str(id(node)))  # for debugging
683
            if node.has_attr():
684
                txt.extend(' `(%s "%s")' % (k, v) for k, v in node.attr.items())
685
            if src:
686
                line, col = line_col(lbreaks, node.pos)
687
688
689
                txt.append(' `(pos %i %i %i)' % (node.pos, line, col))
            elif src is not None and node._pos >= 0:
                txt.append(' `(pos %i)' % node.pos)
Eckhart Arnold's avatar
Eckhart Arnold committed
690
            if root and id(node) in root.error_nodes:
691
                txt.append(" `(err `%s)" % ' '.join(str(err) for err in root.get_errors(node)))
692
            return "".join(txt) + '\n'
693

694
        def closing(node: Node) -> str:
eckhart's avatar
eckhart committed
695
696
            """Returns the closing string for the representation of `node`."""
            return right_bracket
697

698
        def pretty(strg: str) -> str:
eckhart's avatar
eckhart committed
699
700
701
702
            """Encloses `strg` with the right kind of quotation marks."""
            return '"%s"' % strg if strg.find('"') < 0 \
                else "'%s'" % strg if strg.find("'") < 0 \
                else '"%s"' % strg.replace('"', r'\"')
703

704
        sxpr = self._tree_repr(' ' * indentation, opening, closing, pretty, density=density)
eckhart's avatar
eckhart committed
705
        return sxpr if compact else flatten_sxpr(sxpr, flatten_threshold)
Eckhart Arnold's avatar
Eckhart Arnold committed
706

707
708
    def as_xml(self, src: str = None,
               indentation: int = 2,
eckhart's avatar
eckhart committed
709
710
711
               inline_tags: Set[str] = frozenset(),
               omit_tags: Set[str] = frozenset(),
               empty_tags: Set[str] = frozenset()) -> str:
712
713
714
        """
        Returns content as XML-tree.

715
        Args:
716
717
            src:  The source text or `None`. In case the source text is given,
                the position will also be reported as line and column.
718
            indentation: The number of whitespaces for indentation
719
720
721
            inline_tags:  A set of tag names, the content of which will always be written
                on a single line, unless it contains explicit line feeds ('\n').
            omit_tags:  A set of tags from which only the content will be printed, but
722
                neither the opening tag nor its attr nor the closing tag. This
723
724
725
                allows producing a mix of plain text and child tags in the output,
                which otherwise is not supported by the Node object, because it
                requires its content to be either a tuple of children or string content.
726
727
            empty_tags:  A set of tags which shall be rendered as empty elements, e.g.
                "<empty/>" instead of "<empty><empty>".
728
        """
729
        root = cast(RootNode, self) if isinstance(self, RootNode) else None  # type: Optional[RootNode]
730

731
        def opening(node: Node) -> str:
732
733
734
            """Returns the opening string for the representation of `node`."""
            if node.tag_name in omit_tags:
                return ''
eckhart's avatar
eckhart committed
735
            txt = ['<', node.tag_name]
736
            has_reserved_attrs = node.has_attr() \
eckhart's avatar
eckhart committed
737
                and any(r in node.attr for r in {'err', 'line', 'col'})
738
            if node.has_attr():
739
                txt.extend(' %s="%s"' % (k, v) for k, v in node.attr.items())
740
            if src and not has_reserved_attrs:
eckhart's avatar
eckhart committed
741
                txt.append(' line="%i" col="%i"' % line_col(line_breaks, node.pos))
742
            if src == '' and not (node.has_attr() and '_pos' in node.attr) and node.pos >= 0:
743
                txt.append(' _pos="%i"' % node.pos)
Eckhart Arnold's avatar
Eckhart Arnold committed
744
            if root and id(node) in root.error_nodes and not has_reserved_attrs:
eckhart's avatar
eckhart committed
745
                txt.append(' err="%s"' % ''.join(str(err).replace('"', r'\"')
eckhart's avatar
eckhart committed
746
                                                 for err in root.get_errors(node)))
747
748
749
            if node.tag_name in empty_tags:
                assert not node.result, ("Node %s with content %s is not an empty element!" %
                                         (node.tag_name, str(node)))
eckhart's avatar
eckhart committed
750
                ending = "/>\n" if not node.tag_name[0] == '?' else "?>\n"
751
752
753
            else:
                ending = ">\n"
            return "".join(txt + [ending])
754

755
        def closing(node: Node):
756
            """Returns the closing string for the representation of `node`."""
757
            if node.tag_name in omit_tags or node.tag_name in empty_tags:
758
                return ''
eckhart's avatar
eckhart committed
759
            return '\n</' + node.tag_name + '>'
760

761
762
763
764
765
766
        def sanitizer(content: str) -> str:
            """Substitute "&", "<", ">" in XML-content by the respective entities."""
            content = RX_AMP.sub('&amp;', content)
            content = content.replace('<', '&lt;').replace('>', '&gt;')
            return content

767
        def inlining(node: Node):
768
769
770
771
            """Returns True, if `node`'s tag name is contained in `inline_tags`,
            thereby signalling that the children of this node shall not be
            printed on several lines to avoid unwanted gaps in the output.
            """
eckhart's avatar
eckhart committed
772
            return node.tag_name in inline_tags \
773
                or (node.has_attr()
eckhart's avatar
eckhart committed
774
                    and node.attr.get('xml:space', 'default') == 'preserve')
775

776
        line_breaks = linebreaks(src) if src else []
777
        return self._tree_repr(' ' * indentation, opening, closing, sanitizer,
778
                               density=1, inline_fn=inlining)
779

780
    # JSON serialization ###
Eckhart Arnold's avatar
Eckhart Arnold committed
781

Eckhart Arnold's avatar
Eckhart Arnold committed
782
    def to_json_obj(self) -> List:
783
        """Serialize node or tree as JSON-serializable nested list."""
Eckhart Arnold's avatar
Eckhart Arnold committed
784
785
        jo = [self.tag_name,
              [nd.to_json_obj() for nd in self.children] if self.children else str(self.result)]
786
787
        pos = self.pos
        if pos >= 0:
Eckhart Arnold's avatar
Eckhart Arnold committed
788
            jo.append(pos)
789
        if self.has_attr():
Eckhart Arnold's avatar
Eckhart Arnold committed
790
791
            jo.append(dict(self.attr))
        return jo
792

793
    @staticmethod
794
795
    def from_json_obj(json_obj: Union[Dict, Sequence]) -> 'Node':
        """Convert a JSON-object representing a node (or tree) back into a
796
797
        Node object. Raises a ValueError, if `json_obj` does not represent
        a node."""
Eckhart Arnold's avatar
Eckhart Arnold committed
798
799
800
801
        assert isinstance(json_obj, Sequence)
        assert 2 <= len(json_obj) <= 4, str(json_obj)
        if isinstance(json_obj[1], str):
            result = json_obj[1]
802
        else:
Eckhart Arnold's avatar
Eckhart Arnold committed
803
804
805
806
807
808
809
810
            result = tuple(Node.from_json_obj(item) for item in json_obj[1])
        node = Node(json_obj[0], result)
        for extra in json_obj[2:]:
            if isinstance(extra, dict):
                node.attr.update(extra)
            else:
                assert isinstance(extra, int)
                node._pos = extra
811
        return node
812

813
814
815
    def as_json(self, indent: Optional[int] = 2, ensure_ascii=False, simplified=False) -> str:
        return json.dumps(self.to_simplified_json_obj() if simplified else self.to_json_obj(),
                          indent=indent, ensure_ascii=ensure_ascii,
816
817
                          separators=(', ', ': ') if indent is not None else (',', ':'))

818
    # serialization meta-method ###
819

820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
    def serialize_as(self: 'Node', how: str = 'default') -> str:
        """
        Serializes the tree starting with `node` either as S-expression, XML, JSON,
        or in compact form. Possible values for `how` are 'S-expression',
        'XML', 'JSON', 'compact' accordingly, or 'AST', 'CST', 'default' in which case
        the value of respective configuration variable determines the
        serialization format. (See module `configuration.py`.)
        """
        switch = how.lower()

        if switch == 'ast':
            switch = get_config_value('ast_serialization').lower()
        elif switch == 'cst':
            switch = get_config_value('cst_serialization').lower()
        elif switch == 'default':
            switch = get_config_value('default_serialization').lower()

        if switch == SXPRESSION_SERIALIZATION.lower():
            return self.as_sxpr(flatten_threshold=get_config_value('flatten_sxpr_threshold'))
        elif switch == XML_SERIALIZATION.lower():
            return self.as_xml()
        elif switch == JSON_SERIALIZATION.lower():
            return self.as_json()
        elif switch == COMPACT_SERIALIZATION.lower():
            return self.as_sxpr(compact=True)
        else:
            raise ValueError('Unknown serialization %s. Allowed values are either: %s or : %s'
                             % (how, "'ast', 'cst', 'default'", ", ".join(list(SERIALIZATIONS))))
848
849


850
class FrozenNode(Node):
851
852
853
854
    """
    FrozenNode is an immutable kind of Node, i.e. it must not be changed
    after initialization. The purpose is mainly to allow certain kinds of
    optimization, like not having to instantiate empty nodes (because they
855
856
857
    are always the same and will be dropped while parsing, anyway) or,
    rather, throw errors if the program tries to treat a node that is
    supposed to be a temporary (frozen) node as if it was a regular node.
858

859
    Frozen nodes must only be used temporarily during parsing or
860
861
862
    tree-transformation and should not occur in the product of the
    transformation any more. This can be verified with `tree_sanity_check()`.
    """
863
864
865
866
867

    def __init__(self, tag_name: str, result: ResultType) -> None:
        if isinstance(result, str) or isinstance(result, StringView):
            result = str(result)
        else:
868
            raise TypeError('FrozenNode only accepts string as result. '
869
870
871
872
873
874
875
876
877
878
879
                            '(Only leaf-nodes can be frozen nodes.)')
        super(FrozenNode, self).__init__(tag_name, result, True)

    @property
    def result(self) -> StrictResultType:
        return self._result

    @result.setter
    def result(self, result: ResultType):
        raise TypeError('FrozenNode does not allow re-assignment of results.')

eckhart's avatar
eckhart committed
880
881
882
883
    @property
    def attr(self):
        raise AssertionError("Attributes cannot be accessed on a frozen node")

Eckhart Arnold's avatar
Eckhart Arnold committed
884
    def with_pos(self, pos: int) -> 'Node':
885
886
        pass

887
888
889
890
    def to_json_obj(self) -> Dict:
        raise NotImplementedError("Frozen nodes cannot and should not be serialized!")

    @staticmethod
Eckhart Arnold's avatar
Eckhart Arnold committed
891
    def from_json_obj(json_obj: Dict) -> 'Node':
892
893
        raise NotImplementedError("Frozen nodes cannot and should not be deserialized!")

894

895
PLACEHOLDER = FrozenNode('__PLACEHOLDER__', '')
di68kap's avatar
di68kap committed
896
897


898
def tree_sanity_check(tree: Node) -> bool:
899
900
901
902
903
904
905
906
907
    """
    Sanity check for syntax trees: One and the same node must never appear
    twice in the syntax tree. Frozen Nodes (EMTPY_NODE, PLACEHOLDER)
    should only exist temporarily and must have been dropped or eliminated
    before any kind of tree generation (i.e. parsing) or transformation
    is finished.
    :param tree: the root of the tree to be checked
    :return: True, if the tree is `sane`, False otherwise.
    """
908
    node_set = set()  # type: Set[Node]
909
    for node in tree.select(lambda nd: True, include_root=True):
910
        if node in node_set or isinstance(Node, FrozenNode):
911
912
913
914
915
            return False
        node_set.add(node)
    return True


di68kap's avatar
di68kap committed
916
class RootNode(Node):
917
918
919
920
921
922
923
924
925
926
927
928
    """The root node for the syntax tree is a special kind of node that keeps
    and manages global properties of the tree as a whole. These are first and
    foremost the list off errors that occurred during tree generation
    (i.e. parsing) or any transformation of the tree. Other properties concern
    the customization of the XML-serialization.

    The root node can be instantiated before the tree is fully parsed. This is
    necessary, because the root node is needed for managing error messages
    during the parsing process, already. In order to connect the root node to
    the tree, when parsing is finished, the swallow()-method must be called.

        errors (list):  A list of all errors that have occurred so far during
929
930
                processing (i.e. parsing, AST-transformation, compiling)
                of this tree.
di68kap's avatar
di68kap committed
931

932
933
934
935
936
937
        error_nodes (dict): A mapping of node-ids to a list of errors that
                occurred on the node with the respective id.

        error_positions (dict): A mapping of locations to a set of ids of
                nodes that contain an error at that particular location

938
939
        error_flag (int):  the highest warning or error level of all errors
                that occurred.
940
941
942
943
944
945

        inline_tags (set of strings): see `Node.as_xml()` for an explanation.

        omit_tags (set of strings): see `Node.as_xml()` for an explanation.

        empty_tags (set oif strings): see `Node.as_xml()` for an explanation.
di68kap's avatar
di68kap committed
946
    """
947

eckhart's avatar
eckhart committed
948
    def __init__(self, node: Optional[Node] = None):
949
        super().__init__('__not_yet_ready__', '')
950
        self.errors = []               # type: List[Error]
Eckhart Arnold's avatar
Eckhart Arnold committed
951
952
        self.error_nodes = dict()      # type: Dict[int, List[Error]]  # id(node) -> error list
        self.error_positions = dict()  # type: Dict[int, Set[int]]  # pos -> set of id(node)
di68kap's avatar
di68kap committed
953
        self.error_flag = 0
eckhart's avatar
eckhart committed
954
955
        if node is not None:
            self.swallow(node)
956
        # customization for XML-Representation
eckhart's avatar
eckhart committed
957
        self.inline_tags = set()  # type: Set[str]
958
959
        self.omit_tags = set()    # type: Set[str]
        self.empty_tags = set()   # type: Set[str]
di68kap's avatar
di68kap committed
960

961
962
963
964
965
966
967
968
969
    def __deepcopy__(self, memodict={}):
        duplicate = self.__class__(None)
        if self.children:
            duplicate.children = copy.deepcopy(self.children)
            duplicate._result = duplicate.children
        else:
            duplicate.children = NoChildren
            duplicate._result = self._result
        duplicate._pos = self._pos
970
        if self.has_attr():
di68kap's avatar
di68kap committed
971
            duplicate.attr.update(copy.deepcopy(self._xml_attr))
972
            # duplicate._xml_attr = copy.deepcopy(self._xml_attr)  # this is blocked by cython
973
        duplicate.errors = copy.copy(self.errors)
974
975
        duplicate.error_nodes = copy.copy(self.error_nodes)
        duplicate.error_positions = copy.deepcopy(self.error_positions)
976
977
978
979
        duplicate.error_flag = self.error_flag
        duplicate.inline_tags = self.inline_tags
        duplicate.omit_tags = self.omit_tags
        duplicate.empty_tags = self.empty_tags
980
        duplicate.tag_name = self.tag_name
981
982
983
        return duplicate


984
    def swallow(self, node: Node) -> 'RootNode':
985
986
        """
        Put `self` in the place of `node` by copying all its data.
987
988
989
990
991
992
993
994
995
        Returns self.

        This is done by the parse.Grammar object after
        parsing has finished, so that the Grammar object always
        returns a syntax tree rooted in a RootNode object.

        It is possible to add errors to a RootNode object, before it
        has actually swallowed the root of the syntax tree.
        """
di68kap's avatar
di68kap committed
996
997
998
        self._result = node._result
        self.children = node.children
        self._pos = node._pos
999
        self.tag_name = node.tag_name
1000
        if node.has_attr():
1001
            self._xml_attr = node._xml_attr
1002
        # self._content = node._content
Eckhart Arnold's avatar
Eckhart Arnold committed
1003
1004
        if id(node) in self.error_nodes:
            self.error_nodes[id(self)] = self.error_nodes[id(node)]
1005
        return self
di68kap's avatar
di68kap committed
1006

1007
    def add_error(self, node: Optional[Node], error: Error) -> 'RootNode':
1008
1009
1010
        """
        Adds an Error object to the tree, locating it at a specific node.
        """
1011
1012
        if not node:
            node = Node(ZOMBIE_TAG, '').with_pos(error.pos)
1013
        assert node.pos == error.pos or isinstance(node, FrozenNode)
Eckhart Arnold's avatar
Eckhart Arnold committed
1014
1015
        self.error_nodes.setdefault(id(node), []).append(error)
        self.error_positions.setdefault(error.pos, set()).add(id(node))
1016
1017
        self.errors.append(error)
        self.error_flag = max(self.error_flag, error.code)
di68kap's avatar
di68kap committed
1018
1019
        return self