PYTHON 75
Meta.py Guest on 16th April 2021 11:32:09 AM
  1. # -*- coding: utf-8 -*-
  2. """Functions that expose information about templates that might be
  3. interesting for introspection.
  4. """
  5. from . import nodes
  6. from ._compat import iteritems
  7. from ._compat import string_types
  8. from .compiler import CodeGenerator
  9.  
  10.  
  11. class TrackingCodeGenerator(CodeGenerator):
  12.     """We abuse the code generator for introspection."""
  13.  
  14.     def __init__(self, environment):
  15.         CodeGenerator.__init__(self, environment, "<introspection>", "<introspection>")
  16.         self.undeclared_identifiers = set()
  17.  
  18.     def write(self, x):
  19.         """Don't write."""
  20.  
  21.     def enter_frame(self, frame):
  22.         """Remember all undeclared identifiers."""
  23.         CodeGenerator.enter_frame(self, frame)
  24.         for _, (action, param) in iteritems(frame.symbols.loads):
  25.             if action == "resolve" and param not in self.environment.globals:
  26.                 self.undeclared_identifiers.add(param)
  27.  
  28.  
  29. def find_undeclared_variables(ast):
  30.     """Returns a set of all variables in the AST that will be looked up from
  31.    the context at runtime.  Because at compile time it's not known which
  32.    variables will be used depending on the path the execution takes at
  33.    runtime, all variables are returned.
  34.  
  35.    >>> from jinja2 import Environment, meta
  36.    >>> env = Environment()
  37.    >>> ast = env.parse('{% set foo = 42 %}{{ bar + foo }}')
  38.    >>> meta.find_undeclared_variables(ast) == set(['bar'])
  39.    True
  40.  
  41.    .. admonition:: Implementation
  42.  
  43.       Internally the code generator is used for finding undeclared variables.
  44.       This is good to know because the code generator might raise a
  45.       :exc:`TemplateAssertionError` during compilation and as a matter of
  46.       fact this function can currently raise that exception as well.
  47.    """
  48.     codegen = TrackingCodeGenerator(ast.environment)
  49.     codegen.visit(ast)
  50.     return codegen.undeclared_identifiers
  51.  
  52.  
  53. def find_referenced_templates(ast):
  54.     """Finds all the referenced templates from the AST.  This will return an
  55.    iterator over all the hardcoded template extensions, inclusions and
  56.    imports.  If dynamic inheritance or inclusion is used, `None` will be
  57.    yielded.
  58.  
  59.    >>> from jinja2 import Environment, meta
  60.    >>> env = Environment()
  61.    >>> ast = env.parse('{% extends "layout.html" %}{% include helper %}')
  62.    >>> list(meta.find_referenced_templates(ast))
  63.    ['layout.html', None]
  64.  
  65.    This function is useful for dependency tracking.  For example if you want
  66.    to rebuild parts of the website after a layout template has changed.
  67.    """
  68.     for node in ast.find_all(
  69.         (nodes.Extends, nodes.FromImport, nodes.Import, nodes.Include)
  70.     ):
  71.         if not isinstance(node.template, nodes.Const):
  72.             # a tuple with some non consts in there
  73.             if isinstance(node.template, (nodes.Tuple, nodes.List)):
  74.                 for template_name in node.template.items:
  75.                     # something const, only yield the strings and ignore
  76.                     # non-string consts that really just make no sense
  77.                     if isinstance(template_name, nodes.Const):
  78.                         if isinstance(template_name.value, string_types):
  79.                             yield template_name.value
  80.                     # something dynamic in there
  81.                     else:
  82.                         yield None
  83.             # something dynamic we don't know about here
  84.             else:
  85.                 yield None
  86.             continue
  87.         # constant is a basestring, direct template name
  88.         if isinstance(node.template.value, string_types):
  89.             yield node.template.value
  90.         # a tuple or list (latter *should* not happen) made of consts,
  91.         # yield the consts that are strings.  We could warn here for
  92.         # non string values
  93.         elif isinstance(node, nodes.Include) and isinstance(
  94.             node.template.value, (tuple, list)
  95.         ):
  96.             for template_name in node.template.value:
  97.                 if isinstance(template_name, string_types):
  98.                     yield template_name
  99.         # something else we don't care about, we could warn here
  100.         else:
  101.             yield None

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