jinja2/optimizer.py

# -*- 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) 2017 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 generic_visit(self, node, *args, **kwargs):
        node = super(Optimizer, self).generic_visit(node, *args, **kwargs)

        # Do constant folding. Some other nodes besides Expr have
        # as_const, but folding them causes errors later on.
        if isinstance(node, nodes.Expr):
            try:
                return nodes.Const.from_untrusted(
                    node.as_const(args[0] if args else None),
                    lineno=node.lineno,
                    environment=self.environment,
                )
            except nodes.Impossible:
                pass

        return node