third_party/jinja2/optimizer.py

   1 # -*- coding: utf-8 -*-
   2 """
   3     jinja2.optimizer
   4     ~~~~~~~~~~~~~~~~
   5
   6     The jinja optimizer is currently trying to constant fold a few expressions
   7     and modify the AST in place so that it should be easier to evaluate it.
   8
   9     Because the AST does not contain all the scoping information and the
  10     compiler has to find that out, we cannot do all the optimizations we
  11     want.  For example loop unrolling doesn't work because unrolled loops would
  12     have a different scoping.
  13
  14     The solution would be a second syntax tree that has the scoping rules stored.
  15
  16     :copyright: (c) 2010 by the Jinja Team.
  17     :license: BSD.
  18 """
  19 from jinja2 import nodes
  20 from jinja2.visitor import NodeTransformer
  21
  22
  23 def optimize(node, environment):
  24     """The context hint can be used to perform an static optimization
  25     based on the context given."""
  26     optimizer = Optimizer(environment)
  27     return optimizer.visit(node)
  28
  29
  30 class Optimizer(NodeTransformer):
  31
  32     def __init__(self, environment):
  33         self.environment = environment
  34
  35     def visit_If(self, node):
  36         """Eliminate dead code."""
  37         # do not optimize ifs that have a block inside so that it doesn't
  38         # break super().
  39         if node.find(nodes.Block) is not None:
  40             return self.generic_visit(node)
  41         try:
  42             val = self.visit(node.test).as_const()
  43         except nodes.Impossible:
  44             return self.generic_visit(node)
  45         if val:
  46             body = node.body
  47         else:
  48             body = node.else_
  49         result = []
  50         for node in body:
  51             result.extend(self.visit_list(node))
  52         return result
  53
  54     def fold(self, node):
  55         """Do constant folding."""
  56         node = self.generic_visit(node)
  57         try:
  58             return nodes.Const.from_untrusted(node.as_const(),
  59                                               lineno=node.lineno,
  60                                               environment=self.environment)
  61         except nodes.Impossible:
  62             return node
  63
  64     visit_Add = visit_Sub = visit_Mul = visit_Div = visit_FloorDiv = \
  65     visit_Pow = visit_Mod = visit_And = visit_Or = visit_Pos = visit_Neg = \
  66     visit_Not = visit_Compare = visit_Getitem = visit_Getattr = visit_Call = \
  67     visit_Filter = visit_Test = visit_CondExpr = fold
  68     del fold