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210 lines
6.2 KiB
Python
210 lines
6.2 KiB
Python
# ***** BEGIN LICENSE BLOCK *****
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# Version: MPL 1.1/GPL 2.0/LGPL 2.1
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#
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# The contents of this file are subject to the Mozilla Public License Version
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# 1.1 (the "License"); you may not use this file except in compliance with
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# the License. You may obtain a copy of the License at
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# http://www.mozilla.org/MPL/
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#
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# Software distributed under the License is distributed on an "AS IS" basis,
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# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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# for the specific language governing rights and limitations under the
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# License.
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#
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# The Original Code is Mozilla build system.
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#
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# The Initial Developer of the Original Code is
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# Mozilla Foundation.
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# Portions created by the Initial Developer are Copyright (C) 2007
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# the Initial Developer. All Rights Reserved.
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#
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# Contributor(s):
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# Axel Hecht <axel@pike.org>
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#
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# Alternatively, the contents of this file may be used under the terms of
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# either the GNU General Public License Version 2 or later (the "GPL"), or
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# the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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# in which case the provisions of the GPL or the LGPL are applicable instead
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# of those above. If you wish to allow use of your version of this file only
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# under the terms of either the GPL or the LGPL, and not to allow others to
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# use your version of this file under the terms of the MPL, indicate your
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# decision by deleting the provisions above and replace them with the notice
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# and other provisions required by the GPL or the LGPL. If you do not delete
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# the provisions above, a recipient may use your version of this file under
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# the terms of any one of the MPL, the GPL or the LGPL.
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#
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# ***** END LICENSE BLOCK *****
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"""
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Parses and evaluates simple statements for Preprocessor:
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Expression currently supports the following grammar, whitespace is ignored:
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expression :
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unary ( ( '==' | '!=' ) unary ) ? ;
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unary :
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'!'? value ;
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value :
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[0-9]+ # integer
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| \w+ # string identifier or value;
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"""
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import re
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class Expression:
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def __init__(self, expression_string):
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"""
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Create a new expression with this string.
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The expression will already be parsed into an Abstract Syntax Tree.
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"""
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self.content = expression_string
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self.offset = 0
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self.__ignore_whitespace()
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self.e = self.__get_equality()
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if self.content:
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raise Expression.ParseError, self
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def __get_equality(self):
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"""
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Production: unary ( ( '==' | '!=' ) unary ) ?
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"""
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if not len(self.content):
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return None
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rv = Expression.__AST("equality")
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# unary
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rv.append(self.__get_unary())
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self.__ignore_whitespace()
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if not re.match('[=!]=', self.content):
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# no equality needed, short cut to our prime unary
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return rv[0]
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# append operator
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rv.append(Expression.__ASTLeaf('op', self.content[:2]))
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self.__strip(2)
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self.__ignore_whitespace()
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rv.append(self.__get_unary())
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self.__ignore_whitespace()
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return rv
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def __get_unary(self):
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"""
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Production: '!'? value
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"""
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# eat whitespace right away, too
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not_ws = re.match('!\s*', self.content)
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if not not_ws:
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return self.__get_value()
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rv = Expression.__AST('not')
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self.__strip(not_ws.end())
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rv.append(self.__get_value())
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self.__ignore_whitespace()
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return rv
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def __get_value(self):
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"""
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Production: ( [0-9]+ | \w+)
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Note that the order is important, and the expression is kind-of
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ambiguous as \w includes 0-9. One could make it unambiguous by
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removing 0-9 from the first char of a string literal.
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"""
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rv = None
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word_len = re.match('[0-9]*', self.content).end()
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if word_len:
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value = int(self.content[:word_len])
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rv = Expression.__ASTLeaf('int', value)
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else:
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word_len = re.match('\w*', self.content).end()
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if word_len:
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rv = Expression.__ASTLeaf('string', self.content[:word_len])
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else:
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raise Expression.ParseError, self
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self.__strip(word_len)
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self.__ignore_whitespace()
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return rv
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def __ignore_whitespace(self):
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ws_len = re.match('\s*', self.content).end()
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self.__strip(ws_len)
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return
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def __strip(self, length):
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"""
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Remove a given amount of chars from the input and update
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the offset.
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"""
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self.content = self.content[length:]
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self.offset += length
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def evaluate(self, context):
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"""
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Evaluate the expression with the given context
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"""
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# Helper function to evaluate __get_equality results
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def eval_equality(tok):
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left = opmap[tok[0].type](tok[0])
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right = opmap[tok[2].type](tok[2])
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rv = left == right
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if tok[1].value == '!=':
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rv = not rv
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return rv
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# Mapping from token types to evaluator functions
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# Apart from (non-)equality, all these can be simple lambda forms.
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opmap = {
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'equality': eval_equality,
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'not': lambda tok: not opmap[tok[0].type](tok[0]),
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'string': lambda tok: context[tok.value],
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'int': lambda tok: tok.value}
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return opmap[self.e.type](self.e);
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class __AST(list):
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"""
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Internal class implementing Abstract Syntax Tree nodes
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"""
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def __init__(self, type):
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self.type = type
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super(self.__class__, self).__init__(self)
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class __ASTLeaf:
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"""
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Internal class implementing Abstract Syntax Tree leafs
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"""
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def __init__(self, type, value):
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self.value = value
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self.type = type
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def __str__(self):
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return self.value.__str__()
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def __repr__(self):
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return self.value.__repr__()
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class ParseError(StandardError):
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"""
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Error raised when parsing fails.
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It has two members, offset and content, which give the offset of the
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error and the offending content.
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"""
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def __init__(self, expression):
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self.offset = expression.offset
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self.content = expression.content[:3]
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def __str__(self):
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return 'Unexpected content at offset %i, "%s"'%(self.offset, self.content)
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class Context(dict):
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"""
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This class holds variable values by subclassing dict, and while it
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truthfully reports True and False on
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name in context
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it returns the variable name itself on
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context["name"]
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to reflect the ambiguity between string literals and preprocessor
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variables.
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"""
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def __getitem__(self, key):
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if key in self:
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return super(self.__class__, self).__getitem__(key)
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return key
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