Source code for plainbox.impl.xparsers

# This file is part of Checkbox.
#
# Copyright 2012-2015 Canonical Ltd.
# Written by:
#   Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
#
# Checkbox is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 3,
# as published by the Free Software Foundation.
#
# Checkbox is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with Checkbox.  If not, see <http://www.gnu.org/licenses/>.
"""
:mod:`plainbox.impl.xparsers` -- parsers for various plainbox formats
=====================================================================

This module contains parsers for several formats that plainbox has to deal
with. They are not real parsers (as they can be handled with simple regular
expressions most of the time) but rather simple top-down parsing snippets
spread around some classes.

What is interesting though, is the set of classes and their relationships (and
attributes) as that helps to work with the code.


Node and Visitor
----------------
The basic class for everything parsed is :class:`Node`. It contains two
attributes, :attr:`Node.lineno` and :attr:`Node.col_offset` (mimicking the
python AST) and a similar, but not identical visitor mechanism. The precise way
in which the visitor class operates is documented on :class:`Visitor`. In
general application code can freely explore (but not modify as everything is
strictly read-only) the AST.

Regular expressions
-------------------
We have to deal with regular expressions in many places so there's a dedicated
AST node for handling them. The root class is :class:`Re` but it's just a base
for one of the three concrete sub-classes :class:`ReErr`, :class:`ReFixed` and
:class:`RePattern`. ``ReErr`` is an error wrapper (when the regular expression
is incorrect and doesn't work) and the other two (which also share a common
base class :class:`ReOk`) can be used to do text matching. Since other parts of
the code already contain optimizations for regular expressions that are just a
plain string comparison there is a special class to highlight that fact
(``ReFixed``)
"""
import abc
import itertools
import re
import sre_constants
import sre_parse
import sys

from plainbox.i18n import gettext as _
from plainbox.impl import pod
from plainbox.impl.xscanners import WordScanner

__all__ = [
    'Comment',
    'Node',
    'Re',
    'ReErr',
    'ReFixed',
    'ReOk',
    'RePattern',
    'Visitor',
]

Pattern = type(re.compile(""))

afn_typed_const = (pod.typed, pod.const)


def F(doc, type, initial_fn=None):
    """ shortcut for creating fields """
    if type is list:
        return pod.Field(
            doc, type, initial_fn=type,
            assign_filter_list=afn_typed_const)
    else:
        return pod.Field(
            doc, type, pod.MANDATORY,
            assign_filter_list=afn_typed_const)


@pod.modify_field_docstring("not negative")
def not_negative(
    instance: pod.POD, field: pod.Field, old: "Any", new: "Any"
) -> "Any":
    if new < 0:
        raise ValueError("{}.{} cannot be negative".format(
            instance.__class__.__name__, field.name, field.type.__name__))
    return new


[docs]class Node(pod.POD): """ base node type """ lineno = pod.Field( "Line number (1-based)", int, 0, assign_filter_list=[pod.typed, not_negative, pod.const]) col_offset = pod.Field( "Column offset (0-based)", int, 0, assign_filter_list=[pod.typed, not_negative, pod.const]) def __repr__(self): return "{}({})".format( self.__class__.__name__, ', '.join([ '{}={!r}'.format(field.name, getattr(self, field.name)) for field in self.__class__.field_list if field.name not in ('lineno', 'col_offset')]))
[docs] def visit(self, visitor: 'Visitor'): """ Visit all of the sub-nodes reachable from this node :param visitor: Visitor object that gets to explore this and all the other nodes :returns: The return value of the visitor's :meth:`Visitor.visit()` method, if any. The default visitor doesn't return anything. """ return visitor.visit(self)
[docs] def enumerate_entries(self) -> "Generator[node]": for field in self.__class__.field_list: obj = field.__get__(self, self.__class__) if isinstance(obj, Node): yield obj elif isinstance(obj, list): for list_item in obj: if isinstance(list_item, Node): yield list_item
[docs]class Visitor: """ Class assisting in traversing :class:`Node` trees. This class can be used to explore the AST of any of the plainbox-parsed text formats. The way to use this method is to create a custom sub-class of the :class:`Visitor` class and to define methods that correspond to the class of node one is interested in. Example: >>> class Text(Node): ... text = F("text", str) >>> class Group(Node): ... items = F("items", list) >>> class demo_visitor(Visitor): ... def visit_Text_node(self, node: Text): ... print("visiting text node: {}".format(node.text)) ... return self.generic_visit(node) ... def visit_Group_node(self, node: Group): ... print("visiting list node") ... return self.generic_visit(node) >>> Group(items=[ ... Text(text="foo"), Text(text="bar") ... ]).visit(demo_visitor()) visiting list node visiting text node: foo visiting text node: bar """
[docs] def generic_visit(self, node: Node) -> None: """ visit method called on nodes without a dedicated visit method""" # XXX: I don't love the way this works, perhaps we should be less smart # and just require implicit hints as to where to go? Perhaps children # should be something that any node can carry? for child_node in node.enumerate_entries(): self.visit(child_node)
[docs] def visit(self, node: Node) -> "Any": """ visit the specified node """ node_name = node.__class__.__name__ visit_meth_name = 'visit_{}_node'.format(node_name) if hasattr(self, visit_meth_name): visit_meth = getattr(self, visit_meth_name) return visit_meth(node) else: return self.generic_visit(node)
[docs]class Re(Node): """ node representing a regular expression """ text = F("Text of the regular expression (perhaps invalid)", str)
[docs] @staticmethod def parse(text: str, lineno: int=0, col_offset: int=0) -> "Re": """ Parse a bit of text and return a concrete subclass of ``Re`` :param text: The text to parse :returns: If ``text`` is a correct regular expression then an instance of :class:`ReOk` is returned. In practice exactly one of :class:`ReFixed` or :class:`RePattern` may be returned. If ``text`` is incorrect then an instance of :class:`ReErr` is returned. Examples: >>> Re.parse("text") ReFixed(text='text') >>> Re.parse("pa[tT]ern") RePattern(text='pa[tT]ern', re=re.compile('pa[tT]ern')) >>> from sre_constants import error >>> Re.parse("+") ReErr(text='+', exc=error('nothing to repeat',)) """ try: pyre_ast = sre_parse.parse(text) except sre_constants.error as exc: assert len(exc.args) == 1 # XXX: This is a bit crazy but this lets us have identical error # messages across python3.2 all the way to 3.5. I really really # wish there was a better way at fixing this. exc.args = (re.sub(" at position \d+", "", exc.args[0]), ) return ReErr(lineno, col_offset, text, exc) else: # Check if the AST of this regular expression is composed # of just a flat list of 'literal' nodes. In other words, # check if it is a simple string match in disguise if ((sys.version_info[:2] >= (3, 5) and all(t == sre_constants.LITERAL for t, rest in pyre_ast)) or all(t == 'literal' for t, rest in pyre_ast)): return ReFixed(lineno, col_offset, text) else: # NOTE: we might save time by calling some internal function to # convert pyre_ast to the pattern object. return RePattern( lineno, col_offset, text, re.compile(text))
[docs]class ReOk(Re): """ node representing a correct regular expression """
[docs] @abc.abstractmethod def match(self, text: str) -> bool: """ check if the given text matches the expression This method is provided by all of the subclasses of :class:`ReOk`, sometimes the implementation is faster than a naive regular expression match. >>> Re.parse("foo").match("foo") True >>> Re.parse("foo").match("f") False >>> Re.parse("[fF]oo").match("foo") True >>> Re.parse("[fF]oo").match("Foo") True """
[docs]class ReFixed(ReOk): """ node representing a trivial regular expression (fixed string)"""
[docs] def match(self, text: str) -> bool: return text == self.text
[docs]class RePattern(ReOk): """ node representing a regular expression pattern """ re = F("regular expression object", Pattern)
[docs] def match(self, text: str) -> bool: return self.re.match(text) is not None
[docs]class ReErr(Re): """ node representing an incorrect regular expression """ exc = F("exception describing the problem", Exception)
[docs]class Comment(Node): """ node representing single comment """ comment = F("comment text, including any comment markers", str)
class Error(Node): """ node representing a syntax error """ msg = F("message", str) class Text(Node): """ node representing a bit of text """ text = F("text", str) class FieldOverride(Node): """ node representing a single override statement """ value = F("value to apply (override value)", Text) pattern = F("pattern that selects things to override", Re) @staticmethod def parse( text: str, lineno: int=1, col_offset: int=0 ) -> "Union[FieldOverride, Error]": """ Parse a single test plan field override line Using correct syntax will result in a FieldOverride node with appropriate data in the ``value`` and ``pattern`` fields. Note that ``pattern`` may be either a :class:`RePattern` or a :class:`ReFixed` or :class:`ReErr` which is not a valid pattern and cannot be used. >>> FieldOverride.parse("apply new-value to pattern") ... # doctest: +NORMALIZE_WHITESPACE FieldOverride(value=Text(text='new-value'), pattern=ReFixed(text='pattern')) >>> FieldOverride.parse("apply blocker to .*") ... # doctest: +NORMALIZE_WHITESPACE FieldOverride(value=Text(text='blocker'), pattern=RePattern(text='.*', re=re.compile('.*'))) Using incorrect syntax will result in a single Error node being returned. The message (``msg``) field contains useful information on the cause of the problem, as depicted below: >>> FieldOverride.parse("") Error(msg="expected 'apply' near ''") >>> FieldOverride.parse("apply") Error(msg='expected override value') >>> FieldOverride.parse("apply value") Error(msg="expected 'to' near ''") >>> FieldOverride.parse("apply value to") Error(msg='expected override pattern') >>> FieldOverride.parse("apply value to pattern junk") Error(msg="unexpected garbage: 'junk'") Lastly, shell-style comments are supported. They are discarded by the scanner code though. >>> FieldOverride.parse("apply value to pattern # comment") ... # doctest: +NORMALIZE_WHITESPACE FieldOverride(value=Text(text='value'), pattern=ReFixed(text='pattern')) """ # XXX Until our home-grown scanner is ready col_offset values below # are all dummy. This is not strictly critical but should be improved # upon later. scanner = WordScanner(text) # 'APPLY' ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD or lexeme != 'apply': return Error(lineno, col_offset, _("expected {!a} near {!r}").format('apply', lexeme)) # 'APPLY' VALUE ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD: return Error(lineno, col_offset, _("expected override value")) value = Text(lineno, col_offset, lexeme) # 'APPLY' VALUE 'TO' ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD or lexeme != 'to': return Error(lineno, col_offset, _("expected {!a} near {!r}").format('to', lexeme)) # 'APPLY' VALUE 'TO' PATTERN... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD: return Error(lineno, col_offset, _("expected override pattern")) pattern = Re.parse(lexeme, lineno, col_offset) # 'APPLY' VALUE 'TO' PATTERN <EOF> token, lexeme = scanner.get_token() if token != scanner.TokenEnum.EOF: return Error(lineno, col_offset, _("unexpected garbage: {!r}").format(lexeme)) return FieldOverride(lineno, col_offset, value, pattern) class OverrideFieldList(Node): """ node representing a whole plainbox field override list""" entries = pod.Field("a list of comments and patterns", list, initial_fn=list, assign_filter_list=[ pod.typed, pod.typed.sequence(Node), pod.const]) @staticmethod def parse( text: str, lineno: int=1, col_offset: int=0 ) -> "OverrideFieldList": entries = [] initial_lineno = lineno # NOTE: lineno is consciously shadowed below for lineno, line in enumerate(text.splitlines(), lineno): entries.append(FieldOverride.parse(line, lineno, col_offset)) return OverrideFieldList(initial_lineno, col_offset, entries) class OverrideExpression(Node): """ node representing a single override statement """ field = F("field to override", Text) value = F("value to apply", Text) class IncludeStmt(Node): """ node representing a single include statement """ pattern = F("the pattern used for selecting jobs", Re) overrides = pod.Field("list of overrides to apply", list, initial_fn=list, assign_filter_list=[ pod.typed, pod.typed.sequence(OverrideExpression), pod.const]) @staticmethod def parse( text: str, lineno: int=1, col_offset: int=0 ) -> "Union[IncludeStmt, Error]": """ Parse a single test plan include line Using correct syntax will result in a IncludeStmt node with appropriate data in the ``pattern`` and ``overrides`` fields. Note that ``pattern`` may be either a :class:`RePattern` or a :class:`ReFixed` or :class:`ReErr` which is not a valid pattern and cannot be used. Overrides are a list of :class:`OverrideExpression`. The list may contain incorrect, or duplicate values but that's up to higher-level analysis to check for. The whole overrides section is optional so a single pattern is a good include statement: >>> IncludeStmt.parse("usb.*") ... # doctest: +NORMALIZE_WHITESPACE IncludeStmt(pattern=RePattern(text='usb.*', re=re.compile('usb.*')), overrides=[]) Any number of key=value override pairs can be used using commas in between each pair: >>> IncludeStmt.parse("usb.* f1=o1") ... # doctest: +NORMALIZE_WHITESPACE IncludeStmt(pattern=RePattern(text='usb.*', re=re.compile('usb.*')), overrides=[OverrideExpression(field=Text(text='f1'), value=Text(text='o1'))]) >>> IncludeStmt.parse("usb.* f1=o1, f2=o2") ... # doctest: +NORMALIZE_WHITESPACE IncludeStmt(pattern=RePattern(text='usb.*', re=re.compile('usb.*')), overrides=[OverrideExpression(field=Text(text='f1'), value=Text(text='o1')), OverrideExpression(field=Text(text='f2'), value=Text(text='o2'))]) >>> IncludeStmt.parse("usb.* f1=o1, f2=o2, f3=o3") ... # doctest: +NORMALIZE_WHITESPACE IncludeStmt(pattern=RePattern(text='usb.*', re=re.compile('usb.*')), overrides=[OverrideExpression(field=Text(text='f1'), value=Text(text='o1')), OverrideExpression(field=Text(text='f2'), value=Text(text='o2')), OverrideExpression(field=Text(text='f3'), value=Text(text='o3'))]) Obviously some things can fail, the following examples show various error states that are possible. In each state an Error node is returned instead of the whole statement. >>> IncludeStmt.parse("") Error(msg='expected pattern') >>> IncludeStmt.parse("pattern field") Error(msg="expected '='") >>> IncludeStmt.parse("pattern field=") Error(msg='expected override value') >>> IncludeStmt.parse("pattern field=override junk") Error(msg="expected ','") >>> IncludeStmt.parse("pattern field=override, ") Error(msg='expected override field') """ scanner = WordScanner(text) # PATTERN ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD: return Error(lineno, col_offset, _("expected pattern")) pattern = Re.parse(lexeme, lineno, col_offset) overrides = [] for i in itertools.count(): # PATTERN FIELD ... token, lexeme = scanner.get_token() if token == scanner.TokenEnum.EOF and i == 0: # The whole override section is optional so the sequence may # end with EOF on the first iteration of the loop. break elif token != scanner.TokenEnum.WORD: return Error(lineno, col_offset, _("expected override field")) field = Text(lineno, col_offset, lexeme) # PATTERN FIELD = ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.EQUALS: return Error(lineno, col_offset, _("expected '='")) # PATTERN FIELD = VALUE ... token, lexeme = scanner.get_token() if token != scanner.TokenEnum.WORD: return Error(lineno, col_offset, _("expected override value")) value = Text(lineno, col_offset, lexeme) expr = OverrideExpression(lineno, col_offset, field, value) overrides.append(expr) # is there any more? # PATTERN FIELD = VALUE , ... token, lexeme = scanner.get_token() if token == scanner.TokenEnum.COMMA: # (and again) continue elif token == scanner.TokenEnum.EOF: break else: return Error(lineno, col_offset, _("expected ','")) return IncludeStmt(lineno, col_offset, pattern, overrides) class IncludeStmtList(Node): """ node representing a list of include statements""" entries = pod.Field("a list of include statements", list, initial_fn=list, assign_filter_list=[ pod.typed, pod.typed.sequence(Node), pod.const]) @staticmethod def parse( text: str, lineno: int=1, col_offset: int=0 ) -> "IncludeStmtList": """ Parse a multi-line ``include`` field. This field is a simple list of :class:`IncludeStmt` with the added twist that empty lines (including lines containing just irrelevant white-space or comments) are silently ignored. Example: >>> IncludeStmtList.parse(''' ... foo ... # comment ... bar''') ... # doctest: +NORMALIZE_WHITESPACE IncludeStmtList(entries=[IncludeStmt(pattern=ReFixed(text='foo'), overrides=[]), IncludeStmt(pattern=ReFixed(text='bar'), overrides=[])]) """ entries = [] initial_lineno = lineno # NOTE: lineno is consciously shadowed below for lineno, line in enumerate(text.splitlines(), lineno): if WordScanner(line).get_token()[0] == WordScanner.TOKEN_EOF: # XXX: hack to work around the fact that each line is scanned # separately so there is no way to naturally progress to the # next line yet. continue entries.append(IncludeStmt.parse(line, lineno, col_offset)) return IncludeStmtList(initial_lineno, col_offset, entries) class WordList(Node): """ node representing a list of words""" entries = pod.Field("a list of words", list, initial_fn=list, assign_filter_list=[pod.typed, pod.typed.sequence(Node), pod.const]) @staticmethod def parse( text: str, lineno: int=1, col_offset: int=0 ) -> "WordList": """ Parse a list of words. Words are naturally separated by whitespace. Words can be quoted using double quotes. Words can be optionally separated with commas although those are discarded and entirely optional. Some basic examples: >>> WordList.parse("foo, bar") WordList(entries=[Text(text='foo'), Text(text='bar')]) >>> WordList.parse("foo,bar") WordList(entries=[Text(text='foo'), Text(text='bar')]) >>> WordList.parse("foo,,,,bar") WordList(entries=[Text(text='foo'), Text(text='bar')]) >>> WordList.parse("foo,,,,bar,,") WordList(entries=[Text(text='foo'), Text(text='bar')]) Words can be quoted, this allows us to include all kinds of characters inside: >>> WordList.parse('"foo bar"') WordList(entries=[Text(text='foo bar')]) One word of caution, since we use one (and not a very smart one at that) scanner, the equals sign is recognized and rejected as incorrect input. >>> WordList.parse("=") WordList(entries=[Error(msg="Unexpected input: '='")]) """ entries = [] scanner = WordScanner(text) while True: token, lexeme = scanner.get_token() if token == scanner.TOKEN_EOF: break elif token == scanner.TokenEnum.COMMA: continue elif token == scanner.TokenEnum.WORD: entries.append(Text(lineno, col_offset, lexeme)) else: entries.append( Error(lineno, col_offset, "Unexpected input: {!r}".format(lexeme))) return WordList(lineno, col_offset, entries)
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