xref: /openbmc/qemu/scripts/qapi/parser.py (revision f0984d40)
1# -*- coding: utf-8 -*-
2#
3# QAPI schema parser
4#
5# Copyright IBM, Corp. 2011
6# Copyright (c) 2013-2019 Red Hat Inc.
7#
8# Authors:
9#  Anthony Liguori <aliguori@us.ibm.com>
10#  Markus Armbruster <armbru@redhat.com>
11#  Marc-André Lureau <marcandre.lureau@redhat.com>
12#  Kevin Wolf <kwolf@redhat.com>
13#
14# This work is licensed under the terms of the GNU GPL, version 2.
15# See the COPYING file in the top-level directory.
16
17from collections import OrderedDict
18import os
19import re
20from typing import (
21    TYPE_CHECKING,
22    Dict,
23    List,
24    Mapping,
25    Optional,
26    Set,
27    Union,
28)
29
30from .common import must_match
31from .error import QAPISemError, QAPISourceError
32from .source import QAPISourceInfo
33
34
35if TYPE_CHECKING:
36    # pylint: disable=cyclic-import
37    # TODO: Remove cycle. [schema -> expr -> parser -> schema]
38    from .schema import QAPISchemaFeature, QAPISchemaMember
39
40
41# Return value alias for get_expr().
42_ExprValue = Union[List[object], Dict[str, object], str, bool]
43
44
45class QAPIExpression(Dict[str, object]):
46    # pylint: disable=too-few-public-methods
47    def __init__(self,
48                 data: Mapping[str, object],
49                 info: QAPISourceInfo,
50                 doc: Optional['QAPIDoc'] = None):
51        super().__init__(data)
52        self.info = info
53        self.doc: Optional['QAPIDoc'] = doc
54
55
56class QAPIParseError(QAPISourceError):
57    """Error class for all QAPI schema parsing errors."""
58    def __init__(self, parser: 'QAPISchemaParser', msg: str):
59        col = 1
60        for ch in parser.src[parser.line_pos:parser.pos]:
61            if ch == '\t':
62                col = (col + 7) % 8 + 1
63            else:
64                col += 1
65        super().__init__(parser.info, msg, col)
66
67
68class QAPISchemaParser:
69    """
70    Parse QAPI schema source.
71
72    Parse a JSON-esque schema file and process directives.  See
73    qapi-code-gen.txt section "Schema Syntax" for the exact syntax.
74    Grammatical validation is handled later by `expr.check_exprs()`.
75
76    :param fname: Source file name.
77    :param previously_included:
78        The absolute names of previously included source files,
79        if being invoked from another parser.
80    :param incl_info:
81       `QAPISourceInfo` belonging to the parent module.
82       ``None`` implies this is the root module.
83
84    :ivar exprs: Resulting parsed expressions.
85    :ivar docs: Resulting parsed documentation blocks.
86
87    :raise OSError: For problems reading the root schema document.
88    :raise QAPIError: For errors in the schema source.
89    """
90    def __init__(self,
91                 fname: str,
92                 previously_included: Optional[Set[str]] = None,
93                 incl_info: Optional[QAPISourceInfo] = None):
94        self._fname = fname
95        self._included = previously_included or set()
96        self._included.add(os.path.abspath(self._fname))
97        self.src = ''
98
99        # Lexer state (see `accept` for details):
100        self.info = QAPISourceInfo(self._fname, incl_info)
101        self.tok: Union[None, str] = None
102        self.pos = 0
103        self.cursor = 0
104        self.val: Optional[Union[bool, str]] = None
105        self.line_pos = 0
106
107        # Parser output:
108        self.exprs: List[QAPIExpression] = []
109        self.docs: List[QAPIDoc] = []
110
111        # Showtime!
112        self._parse()
113
114    def _parse(self) -> None:
115        """
116        Parse the QAPI schema document.
117
118        :return: None.  Results are stored in ``.exprs`` and ``.docs``.
119        """
120        cur_doc = None
121
122        # May raise OSError; allow the caller to handle it.
123        with open(self._fname, 'r', encoding='utf-8') as fp:
124            self.src = fp.read()
125        if self.src == '' or self.src[-1] != '\n':
126            self.src += '\n'
127
128        # Prime the lexer:
129        self.accept()
130
131        # Parse until done:
132        while self.tok is not None:
133            info = self.info
134            if self.tok == '#':
135                self.reject_expr_doc(cur_doc)
136                for cur_doc in self.get_doc(info):
137                    self.docs.append(cur_doc)
138                continue
139
140            expr = self.get_expr()
141            if not isinstance(expr, dict):
142                raise QAPISemError(
143                    info, "top-level expression must be an object")
144
145            if 'include' in expr:
146                self.reject_expr_doc(cur_doc)
147                if len(expr) != 1:
148                    raise QAPISemError(info, "invalid 'include' directive")
149                include = expr['include']
150                if not isinstance(include, str):
151                    raise QAPISemError(info,
152                                       "value of 'include' must be a string")
153                incl_fname = os.path.join(os.path.dirname(self._fname),
154                                          include)
155                self._add_expr(OrderedDict({'include': incl_fname}), info)
156                exprs_include = self._include(include, info, incl_fname,
157                                              self._included)
158                if exprs_include:
159                    self.exprs.extend(exprs_include.exprs)
160                    self.docs.extend(exprs_include.docs)
161            elif "pragma" in expr:
162                self.reject_expr_doc(cur_doc)
163                if len(expr) != 1:
164                    raise QAPISemError(info, "invalid 'pragma' directive")
165                pragma = expr['pragma']
166                if not isinstance(pragma, dict):
167                    raise QAPISemError(
168                        info, "value of 'pragma' must be an object")
169                for name, value in pragma.items():
170                    self._pragma(name, value, info)
171            else:
172                if cur_doc and not cur_doc.symbol:
173                    raise QAPISemError(
174                        cur_doc.info, "definition documentation required")
175                self._add_expr(expr, info, cur_doc)
176            cur_doc = None
177        self.reject_expr_doc(cur_doc)
178
179    def _add_expr(self, expr: Mapping[str, object],
180                  info: QAPISourceInfo,
181                  doc: Optional['QAPIDoc'] = None) -> None:
182        self.exprs.append(QAPIExpression(expr, info, doc))
183
184    @staticmethod
185    def reject_expr_doc(doc: Optional['QAPIDoc']) -> None:
186        if doc and doc.symbol:
187            raise QAPISemError(
188                doc.info,
189                "documentation for '%s' is not followed by the definition"
190                % doc.symbol)
191
192    @staticmethod
193    def _include(include: str,
194                 info: QAPISourceInfo,
195                 incl_fname: str,
196                 previously_included: Set[str]
197                 ) -> Optional['QAPISchemaParser']:
198        incl_abs_fname = os.path.abspath(incl_fname)
199        # catch inclusion cycle
200        inf: Optional[QAPISourceInfo] = info
201        while inf:
202            if incl_abs_fname == os.path.abspath(inf.fname):
203                raise QAPISemError(info, "inclusion loop for %s" % include)
204            inf = inf.parent
205
206        # skip multiple include of the same file
207        if incl_abs_fname in previously_included:
208            return None
209
210        try:
211            return QAPISchemaParser(incl_fname, previously_included, info)
212        except OSError as err:
213            raise QAPISemError(
214                info,
215                f"can't read include file '{incl_fname}': {err.strerror}"
216            ) from err
217
218    @staticmethod
219    def _pragma(name: str, value: object, info: QAPISourceInfo) -> None:
220
221        def check_list_str(name: str, value: object) -> List[str]:
222            if (not isinstance(value, list) or
223                    any(not isinstance(elt, str) for elt in value)):
224                raise QAPISemError(
225                    info,
226                    "pragma %s must be a list of strings" % name)
227            return value
228
229        pragma = info.pragma
230
231        if name == 'doc-required':
232            if not isinstance(value, bool):
233                raise QAPISemError(info,
234                                   "pragma 'doc-required' must be boolean")
235            pragma.doc_required = value
236        elif name == 'command-name-exceptions':
237            pragma.command_name_exceptions = check_list_str(name, value)
238        elif name == 'command-returns-exceptions':
239            pragma.command_returns_exceptions = check_list_str(name, value)
240        elif name == 'member-name-exceptions':
241            pragma.member_name_exceptions = check_list_str(name, value)
242        else:
243            raise QAPISemError(info, "unknown pragma '%s'" % name)
244
245    def accept(self, skip_comment: bool = True) -> None:
246        """
247        Read and store the next token.
248
249        :param skip_comment:
250            When false, return COMMENT tokens ("#").
251            This is used when reading documentation blocks.
252
253        :return:
254            None.  Several instance attributes are updated instead:
255
256            - ``.tok`` represents the token type.  See below for values.
257            - ``.info`` describes the token's source location.
258            - ``.val`` is the token's value, if any.  See below.
259            - ``.pos`` is the buffer index of the first character of
260              the token.
261
262        * Single-character tokens:
263
264            These are "{", "}", ":", ",", "[", and "]".
265            ``.tok`` holds the single character and ``.val`` is None.
266
267        * Multi-character tokens:
268
269          * COMMENT:
270
271            This token is not normally returned by the lexer, but it can
272            be when ``skip_comment`` is False.  ``.tok`` is "#", and
273            ``.val`` is a string including all chars until end-of-line,
274            including the "#" itself.
275
276          * STRING:
277
278            ``.tok`` is "'", the single quote.  ``.val`` contains the
279            string, excluding the surrounding quotes.
280
281          * TRUE and FALSE:
282
283            ``.tok`` is either "t" or "f", ``.val`` will be the
284            corresponding bool value.
285
286          * EOF:
287
288            ``.tok`` and ``.val`` will both be None at EOF.
289        """
290        while True:
291            self.tok = self.src[self.cursor]
292            self.pos = self.cursor
293            self.cursor += 1
294            self.val = None
295
296            if self.tok == '#':
297                if self.src[self.cursor] == '#':
298                    # Start of doc comment
299                    skip_comment = False
300                self.cursor = self.src.find('\n', self.cursor)
301                if not skip_comment:
302                    self.val = self.src[self.pos:self.cursor]
303                    return
304            elif self.tok in '{}:,[]':
305                return
306            elif self.tok == "'":
307                # Note: we accept only printable ASCII
308                string = ''
309                esc = False
310                while True:
311                    ch = self.src[self.cursor]
312                    self.cursor += 1
313                    if ch == '\n':
314                        raise QAPIParseError(self, "missing terminating \"'\"")
315                    if esc:
316                        # Note: we recognize only \\ because we have
317                        # no use for funny characters in strings
318                        if ch != '\\':
319                            raise QAPIParseError(self,
320                                                 "unknown escape \\%s" % ch)
321                        esc = False
322                    elif ch == '\\':
323                        esc = True
324                        continue
325                    elif ch == "'":
326                        self.val = string
327                        return
328                    if ord(ch) < 32 or ord(ch) >= 127:
329                        raise QAPIParseError(
330                            self, "funny character in string")
331                    string += ch
332            elif self.src.startswith('true', self.pos):
333                self.val = True
334                self.cursor += 3
335                return
336            elif self.src.startswith('false', self.pos):
337                self.val = False
338                self.cursor += 4
339                return
340            elif self.tok == '\n':
341                if self.cursor == len(self.src):
342                    self.tok = None
343                    return
344                self.info = self.info.next_line()
345                self.line_pos = self.cursor
346            elif not self.tok.isspace():
347                # Show up to next structural, whitespace or quote
348                # character
349                match = must_match('[^[\\]{}:,\\s\'"]+',
350                                   self.src[self.cursor-1:])
351                raise QAPIParseError(self, "stray '%s'" % match.group(0))
352
353    def get_members(self) -> Dict[str, object]:
354        expr: Dict[str, object] = OrderedDict()
355        if self.tok == '}':
356            self.accept()
357            return expr
358        if self.tok != "'":
359            raise QAPIParseError(self, "expected string or '}'")
360        while True:
361            key = self.val
362            assert isinstance(key, str)  # Guaranteed by tok == "'"
363
364            self.accept()
365            if self.tok != ':':
366                raise QAPIParseError(self, "expected ':'")
367            self.accept()
368            if key in expr:
369                raise QAPIParseError(self, "duplicate key '%s'" % key)
370            expr[key] = self.get_expr()
371            if self.tok == '}':
372                self.accept()
373                return expr
374            if self.tok != ',':
375                raise QAPIParseError(self, "expected ',' or '}'")
376            self.accept()
377            if self.tok != "'":
378                raise QAPIParseError(self, "expected string")
379
380    def get_values(self) -> List[object]:
381        expr: List[object] = []
382        if self.tok == ']':
383            self.accept()
384            return expr
385        if self.tok not in tuple("{['tf"):
386            raise QAPIParseError(
387                self, "expected '{', '[', ']', string, or boolean")
388        while True:
389            expr.append(self.get_expr())
390            if self.tok == ']':
391                self.accept()
392                return expr
393            if self.tok != ',':
394                raise QAPIParseError(self, "expected ',' or ']'")
395            self.accept()
396
397    def get_expr(self) -> _ExprValue:
398        expr: _ExprValue
399        if self.tok == '{':
400            self.accept()
401            expr = self.get_members()
402        elif self.tok == '[':
403            self.accept()
404            expr = self.get_values()
405        elif self.tok in tuple("'tf"):
406            assert isinstance(self.val, (str, bool))
407            expr = self.val
408            self.accept()
409        else:
410            raise QAPIParseError(
411                self, "expected '{', '[', string, or boolean")
412        return expr
413
414    def get_doc(self, info: QAPISourceInfo) -> List['QAPIDoc']:
415        if self.val != '##':
416            raise QAPIParseError(
417                self, "junk after '##' at start of documentation comment")
418
419        docs = []
420        cur_doc = QAPIDoc(self, info)
421        self.accept(False)
422        while self.tok == '#':
423            assert isinstance(self.val, str)
424            if self.val.startswith('##'):
425                # End of doc comment
426                if self.val != '##':
427                    raise QAPIParseError(
428                        self,
429                        "junk after '##' at end of documentation comment")
430                cur_doc.end_comment()
431                docs.append(cur_doc)
432                self.accept()
433                return docs
434            if self.val.startswith('# ='):
435                if cur_doc.symbol:
436                    raise QAPIParseError(
437                        self,
438                        "unexpected '=' markup in definition documentation")
439                if cur_doc.body.text:
440                    cur_doc.end_comment()
441                    docs.append(cur_doc)
442                    cur_doc = QAPIDoc(self, info)
443            cur_doc.append(self.val)
444            self.accept(False)
445
446        raise QAPIParseError(self, "documentation comment must end with '##'")
447
448
449class QAPIDoc:
450    """
451    A documentation comment block, either definition or free-form
452
453    Definition documentation blocks consist of
454
455    * a body section: one line naming the definition, followed by an
456      overview (any number of lines)
457
458    * argument sections: a description of each argument (for commands
459      and events) or member (for structs, unions and alternates)
460
461    * features sections: a description of each feature flag
462
463    * additional (non-argument) sections, possibly tagged
464
465    Free-form documentation blocks consist only of a body section.
466    """
467
468    class Section:
469        # pylint: disable=too-few-public-methods
470        def __init__(self, parser: QAPISchemaParser,
471                     name: Optional[str] = None, indent: int = 0):
472
473            # parser, for error messages about indentation
474            self._parser = parser
475            # optional section name (argument/member or section name)
476            self.name = name
477            self.text = ''
478            # the expected indent level of the text of this section
479            self._indent = indent
480
481        def append(self, line: str) -> None:
482            # Strip leading spaces corresponding to the expected indent level
483            # Blank lines are always OK.
484            if line:
485                indent = must_match(r'\s*', line).end()
486                if indent < self._indent:
487                    raise QAPIParseError(
488                        self._parser,
489                        "unexpected de-indent (expected at least %d spaces)" %
490                        self._indent)
491                line = line[self._indent:]
492
493            self.text += line.rstrip() + '\n'
494
495    class ArgSection(Section):
496        def __init__(self, parser: QAPISchemaParser,
497                     name: str, indent: int = 0):
498            super().__init__(parser, name, indent)
499            self.member: Optional['QAPISchemaMember'] = None
500
501        def connect(self, member: 'QAPISchemaMember') -> None:
502            self.member = member
503
504    class NullSection(Section):
505        """
506        Immutable dummy section for use at the end of a doc block.
507        """
508        # pylint: disable=too-few-public-methods
509        def append(self, line: str) -> None:
510            assert False, "Text appended after end_comment() called."
511
512    def __init__(self, parser: QAPISchemaParser, info: QAPISourceInfo):
513        # self._parser is used to report errors with QAPIParseError.  The
514        # resulting error position depends on the state of the parser.
515        # It happens to be the beginning of the comment.  More or less
516        # servicable, but action at a distance.
517        self._parser = parser
518        self.info = info
519        self.symbol: Optional[str] = None
520        self.body = QAPIDoc.Section(parser)
521        # dicts mapping parameter/feature names to their ArgSection
522        self.args: Dict[str, QAPIDoc.ArgSection] = OrderedDict()
523        self.features: Dict[str, QAPIDoc.ArgSection] = OrderedDict()
524        self.sections: List[QAPIDoc.Section] = []
525        # the current section
526        self._section = self.body
527        self._append_line = self._append_body_line
528
529    def has_section(self, name: str) -> bool:
530        """Return True if we have a section with this name."""
531        for i in self.sections:
532            if i.name == name:
533                return True
534        return False
535
536    def append(self, line: str) -> None:
537        """
538        Parse a comment line and add it to the documentation.
539
540        The way that the line is dealt with depends on which part of
541        the documentation we're parsing right now:
542        * The body section: ._append_line is ._append_body_line
543        * An argument section: ._append_line is ._append_args_line
544        * A features section: ._append_line is ._append_features_line
545        * An additional section: ._append_line is ._append_various_line
546        """
547        line = line[1:]
548        if not line:
549            self._append_freeform(line)
550            return
551
552        if line[0] != ' ':
553            raise QAPIParseError(self._parser, "missing space after #")
554        line = line[1:]
555        self._append_line(line)
556
557    def end_comment(self) -> None:
558        self._switch_section(QAPIDoc.NullSection(self._parser))
559
560    @staticmethod
561    def _is_section_tag(name: str) -> bool:
562        return name in ('Returns:', 'Since:',
563                        # those are often singular or plural
564                        'Note:', 'Notes:',
565                        'Example:', 'Examples:',
566                        'TODO:')
567
568    def _append_body_line(self, line: str) -> None:
569        """
570        Process a line of documentation text in the body section.
571
572        If this a symbol line and it is the section's first line, this
573        is a definition documentation block for that symbol.
574
575        If it's a definition documentation block, another symbol line
576        begins the argument section for the argument named by it, and
577        a section tag begins an additional section.  Start that
578        section and append the line to it.
579
580        Else, append the line to the current section.
581        """
582        name = line.split(' ', 1)[0]
583        # FIXME not nice: things like '#  @foo:' and '# @foo: ' aren't
584        # recognized, and get silently treated as ordinary text
585        if not self.symbol and not self.body.text and line.startswith('@'):
586            if not line.endswith(':'):
587                raise QAPIParseError(self._parser, "line should end with ':'")
588            self.symbol = line[1:-1]
589            # Invalid names are not checked here, but the name provided MUST
590            # match the following definition, which *is* validated in expr.py.
591            if not self.symbol:
592                raise QAPIParseError(
593                    self._parser, "name required after '@'")
594        elif self.symbol:
595            # This is a definition documentation block
596            if name.startswith('@') and name.endswith(':'):
597                self._append_line = self._append_args_line
598                self._append_args_line(line)
599            elif line == 'Features:':
600                self._append_line = self._append_features_line
601            elif self._is_section_tag(name):
602                self._append_line = self._append_various_line
603                self._append_various_line(line)
604            else:
605                self._append_freeform(line)
606        else:
607            # This is a free-form documentation block
608            self._append_freeform(line)
609
610    def _append_args_line(self, line: str) -> None:
611        """
612        Process a line of documentation text in an argument section.
613
614        A symbol line begins the next argument section, a section tag
615        section or a non-indented line after a blank line begins an
616        additional section.  Start that section and append the line to
617        it.
618
619        Else, append the line to the current section.
620
621        """
622        name = line.split(' ', 1)[0]
623
624        if name.startswith('@') and name.endswith(':'):
625            # If line is "@arg:   first line of description", find
626            # the index of 'f', which is the indent we expect for any
627            # following lines.  We then remove the leading "@arg:"
628            # from line and replace it with spaces so that 'f' has the
629            # same index as it did in the original line and can be
630            # handled the same way we will handle following lines.
631            indent = must_match(r'@\S*:\s*', line).end()
632            line = line[indent:]
633            if not line:
634                # Line was just the "@arg:" header; following lines
635                # are not indented
636                indent = 0
637            else:
638                line = ' ' * indent + line
639            self._start_args_section(name[1:-1], indent)
640        elif self._is_section_tag(name):
641            self._append_line = self._append_various_line
642            self._append_various_line(line)
643            return
644        elif (self._section.text.endswith('\n\n')
645              and line and not line[0].isspace()):
646            if line == 'Features:':
647                self._append_line = self._append_features_line
648            else:
649                self._start_section()
650                self._append_line = self._append_various_line
651                self._append_various_line(line)
652            return
653
654        self._append_freeform(line)
655
656    def _append_features_line(self, line: str) -> None:
657        name = line.split(' ', 1)[0]
658
659        if name.startswith('@') and name.endswith(':'):
660            # If line is "@arg:   first line of description", find
661            # the index of 'f', which is the indent we expect for any
662            # following lines.  We then remove the leading "@arg:"
663            # from line and replace it with spaces so that 'f' has the
664            # same index as it did in the original line and can be
665            # handled the same way we will handle following lines.
666            indent = must_match(r'@\S*:\s*', line).end()
667            line = line[indent:]
668            if not line:
669                # Line was just the "@arg:" header; following lines
670                # are not indented
671                indent = 0
672            else:
673                line = ' ' * indent + line
674            self._start_features_section(name[1:-1], indent)
675        elif self._is_section_tag(name):
676            self._append_line = self._append_various_line
677            self._append_various_line(line)
678            return
679        elif (self._section.text.endswith('\n\n')
680              and line and not line[0].isspace()):
681            self._start_section()
682            self._append_line = self._append_various_line
683            self._append_various_line(line)
684            return
685
686        self._append_freeform(line)
687
688    def _append_various_line(self, line: str) -> None:
689        """
690        Process a line of documentation text in an additional section.
691
692        A symbol line is an error.
693
694        A section tag begins an additional section.  Start that
695        section and append the line to it.
696
697        Else, append the line to the current section.
698        """
699        name = line.split(' ', 1)[0]
700
701        if name.startswith('@') and name.endswith(':'):
702            raise QAPIParseError(self._parser,
703                                 "'%s' can't follow '%s' section"
704                                 % (name, self.sections[0].name))
705        if self._is_section_tag(name):
706            # If line is "Section:   first line of description", find
707            # the index of 'f', which is the indent we expect for any
708            # following lines.  We then remove the leading "Section:"
709            # from line and replace it with spaces so that 'f' has the
710            # same index as it did in the original line and can be
711            # handled the same way we will handle following lines.
712            indent = must_match(r'\S*:\s*', line).end()
713            line = line[indent:]
714            if not line:
715                # Line was just the "Section:" header; following lines
716                # are not indented
717                indent = 0
718            else:
719                line = ' ' * indent + line
720            self._start_section(name[:-1], indent)
721
722        self._append_freeform(line)
723
724    def _start_symbol_section(
725            self,
726            symbols_dict: Dict[str, 'QAPIDoc.ArgSection'],
727            name: str,
728            indent: int) -> None:
729        # FIXME invalid names other than the empty string aren't flagged
730        if not name:
731            raise QAPIParseError(self._parser, "invalid parameter name")
732        if name in symbols_dict:
733            raise QAPIParseError(self._parser,
734                                 "'%s' parameter name duplicated" % name)
735        assert not self.sections
736        new_section = QAPIDoc.ArgSection(self._parser, name, indent)
737        self._switch_section(new_section)
738        symbols_dict[name] = new_section
739
740    def _start_args_section(self, name: str, indent: int) -> None:
741        self._start_symbol_section(self.args, name, indent)
742
743    def _start_features_section(self, name: str, indent: int) -> None:
744        self._start_symbol_section(self.features, name, indent)
745
746    def _start_section(self, name: Optional[str] = None,
747                       indent: int = 0) -> None:
748        if name in ('Returns', 'Since') and self.has_section(name):
749            raise QAPIParseError(self._parser,
750                                 "duplicated '%s' section" % name)
751        new_section = QAPIDoc.Section(self._parser, name, indent)
752        self._switch_section(new_section)
753        self.sections.append(new_section)
754
755    def _switch_section(self, new_section: 'QAPIDoc.Section') -> None:
756        text = self._section.text = self._section.text.strip()
757
758        # Only the 'body' section is allowed to have an empty body.
759        # All other sections, including anonymous ones, must have text.
760        if self._section != self.body and not text:
761            # We do not create anonymous sections unless there is
762            # something to put in them; this is a parser bug.
763            assert self._section.name
764            raise QAPIParseError(
765                self._parser,
766                "empty doc section '%s'" % self._section.name)
767
768        self._section = new_section
769
770    def _append_freeform(self, line: str) -> None:
771        match = re.match(r'(@\S+:)', line)
772        if match:
773            raise QAPIParseError(self._parser,
774                                 "'%s' not allowed in free-form documentation"
775                                 % match.group(1))
776        self._section.append(line)
777
778    def connect_member(self, member: 'QAPISchemaMember') -> None:
779        if member.name not in self.args:
780            # Undocumented TODO outlaw
781            self.args[member.name] = QAPIDoc.ArgSection(self._parser,
782                                                        member.name)
783        self.args[member.name].connect(member)
784
785    def connect_feature(self, feature: 'QAPISchemaFeature') -> None:
786        if feature.name not in self.features:
787            raise QAPISemError(feature.info,
788                               "feature '%s' lacks documentation"
789                               % feature.name)
790        self.features[feature.name].connect(feature)
791
792    def check_expr(self, expr: QAPIExpression) -> None:
793        if self.has_section('Returns') and 'command' not in expr:
794            raise QAPISemError(self.info,
795                               "'Returns:' is only valid for commands")
796
797    def check(self) -> None:
798
799        def check_args_section(
800                args: Dict[str, QAPIDoc.ArgSection], what: str
801        ) -> None:
802            bogus = [name for name, section in args.items()
803                     if not section.member]
804            if bogus:
805                raise QAPISemError(
806                    self.info,
807                    "documented %s%s '%s' %s not exist" % (
808                        what,
809                        "s" if len(bogus) > 1 else "",
810                        "', '".join(bogus),
811                        "do" if len(bogus) > 1 else "does"
812                    ))
813
814        check_args_section(self.args, 'member')
815        check_args_section(self.features, 'feature')
816