Add Python templating engine Jinja2 to third_party

third_party/jinja2/optimizer.py

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