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Viewing changes to hooks/lib/jinja2/optimizer.py

  • Committer: Robin Winslow
  • Date: 2014-05-27 14:00:44 UTC
  • Revision ID: robin.winslow@canonical.com-20140527140044-8rpmb3wx4djzwa83
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hooks/lib/jinja2/optimizer.py
 
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# -*- coding: utf-8 -*-
 
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"""
 
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    jinja2.optimizer
 
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    ~~~~~~~~~~~~~~~~
 
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    The jinja optimizer is currently trying to constant fold a few expressions
 
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    and modify the AST in place so that it should be easier to evaluate it.
 
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    Because the AST does not contain all the scoping information and the
 
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    compiler has to find that out, we cannot do all the optimizations we
 
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    want.  For example loop unrolling doesn't work because unrolled loops would
 
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    have a different scoping.
 
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    The solution would be a second syntax tree that has the scoping rules stored.
 
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    :copyright: (c) 2010 by the Jinja Team.
 
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    :license: BSD.
 
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"""
 
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from jinja2 import nodes
 
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from jinja2.visitor import NodeTransformer
 
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def optimize(node, environment):
 
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    """The context hint can be used to perform an static optimization
 
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    based on the context given."""
 
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    optimizer = Optimizer(environment)
 
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    return optimizer.visit(node)
 
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class Optimizer(NodeTransformer):
 
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    def __init__(self, environment):
 
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        self.environment = environment
 
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    def visit_If(self, node):
 
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        """Eliminate dead code."""
 
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        # do not optimize ifs that have a block inside so that it doesn't
 
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        # break super().
 
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        if node.find(nodes.Block) is not None:
 
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            return self.generic_visit(node)
 
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        try:
 
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            val = self.visit(node.test).as_const()
 
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        except nodes.Impossible:
 
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            return self.generic_visit(node)
 
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        if val:
 
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            body = node.body
 
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        else:
 
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            body = node.else_
 
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        result = []
 
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        for node in body:
 
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            result.extend(self.visit_list(node))
 
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        return result
 
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    def fold(self, node):
 
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        """Do constant folding."""
 
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        node = self.generic_visit(node)
 
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        try:
 
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            return nodes.Const.from_untrusted(node.as_const(),
 
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                                              lineno=node.lineno,
 
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                                              environment=self.environment)
 
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        except nodes.Impossible:
 
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            return node
 
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    visit_Add = visit_Sub = visit_Mul = visit_Div = visit_FloorDiv = \
 
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    visit_Pow = visit_Mod = visit_And = visit_Or = visit_Pos = visit_Neg = \
 
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    visit_Not = visit_Compare = visit_Getitem = visit_Getattr = visit_Call = \
 
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    visit_Filter = visit_Test = visit_CondExpr = fold
 
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    del fold