third_party/jinja2/meta.py

   1 # -*- coding: utf-8 -*-
   2 """
   3     jinja2.meta
   4     ~~~~~~~~~~~
   5
   6     This module implements various functions that exposes information about
   7     templates that might be interesting for various kinds of applications.
   8
   9     :copyright: (c) 2010 by the Jinja Team, see AUTHORS for more details.
  10     :license: BSD, see LICENSE for more details.
  11 """
  12 from jinja2 import nodes
  13 from jinja2.compiler import CodeGenerator
  14 from jinja2._compat import string_types
  15
  16
  17 class TrackingCodeGenerator(CodeGenerator):
  18     """We abuse the code generator for introspection."""
  19
  20     def __init__(self, environment):
  21         CodeGenerator.__init__(self, environment, '<introspection>',
  22                                '<introspection>')
  23         self.undeclared_identifiers = set()
  24
  25     def write(self, x):
  26         """Don't write."""
  27
  28     def pull_locals(self, frame):
  29         """Remember all undeclared identifiers."""
  30         self.undeclared_identifiers.update(frame.identifiers.undeclared)
  31
  32
  33 def find_undeclared_variables(ast):
  34     """Returns a set of all variables in the AST that will be looked up from
  35     the context at runtime.  Because at compile time it's not known which
  36     variables will be used depending on the path the execution takes at
  37     runtime, all variables are returned.
  38
  39     >>> from jinja2 import Environment, meta
  40     >>> env = Environment()
  41     >>> ast = env.parse('{% set foo = 42 %}{{ bar + foo }}')
  42     >>> meta.find_undeclared_variables(ast)
  43     set(['bar'])
  44
  45     .. admonition:: Implementation
  46
  47        Internally the code generator is used for finding undeclared variables.
  48        This is good to know because the code generator might raise a
  49        :exc:`TemplateAssertionError` during compilation and as a matter of
  50        fact this function can currently raise that exception as well.
  51     """
  52     codegen = TrackingCodeGenerator(ast.environment)
  53     codegen.visit(ast)
  54     return codegen.undeclared_identifiers
  55
  56
  57 def find_referenced_templates(ast):
  58     """Finds all the referenced templates from the AST.  This will return an
  59     iterator over all the hardcoded template extensions, inclusions and
  60     imports.  If dynamic inheritance or inclusion is used, `None` will be
  61     yielded.
  62
  63     >>> from jinja2 import Environment, meta
  64     >>> env = Environment()
  65     >>> ast = env.parse('{% extends "layout.html" %}{% include helper %}')
  66     >>> list(meta.find_referenced_templates(ast))
  67     ['layout.html', None]
  68
  69     This function is useful for dependency tracking.  For example if you want
  70     to rebuild parts of the website after a layout template has changed.
  71     """
  72     for node in ast.find_all((nodes.Extends, nodes.FromImport, nodes.Import,
  73                               nodes.Include)):
  74         if not isinstance(node.template, nodes.Const):
  75             # a tuple with some non consts in there
  76             if isinstance(node.template, (nodes.Tuple, nodes.List)):
  77                 for template_name in node.template.items:
  78                     # something const, only yield the strings and ignore
  79                     # non-string consts that really just make no sense
  80                     if isinstance(template_name, nodes.Const):
  81                         if isinstance(template_name.value, string_types):
  82                             yield template_name.value
  83                     # something dynamic in there
  84                     else:
  85                         yield None
  86             # something dynamic we don't know about here
  87             else:
  88                 yield None
  89             continue
  90         # constant is a basestring, direct template name
  91         if isinstance(node.template.value, string_types):
  92             yield node.template.value
  93         # a tuple or list (latter *should* not happen) made of consts,
  94         # yield the consts that are strings.  We could warn here for
  95         # non string values
  96         elif isinstance(node, nodes.Include) and \
  97              isinstance(node.template.value, (tuple, list)):
  98             for template_name in node.template.value:
  99                 if isinstance(template_name, string_types):
 100                     yield template_name
 101         # something else we don't care about, we could warn here
 102         else:
 103             yield None