jinja2.meta

  1"""Functions that expose information about templates that might be
  2interesting for introspection.
  3"""
  4
  5import typing as t
  6
  7from . import nodes
  8from .compiler import CodeGenerator
  9from .compiler import Frame
 10
 11if t.TYPE_CHECKING:
 12    from .environment import Environment
 13
 14
 15class TrackingCodeGenerator(CodeGenerator):
 16    """We abuse the code generator for introspection."""
 17
 18    def __init__(self, environment: "Environment") -> None:
 19        super().__init__(environment, "<introspection>", "<introspection>")
 20        self.undeclared_identifiers: t.Set[str] = set()
 21
 22    def write(self, x: str) -> None:
 23        """Don't write."""
 24
 25    def enter_frame(self, frame: Frame) -> None:
 26        """Remember all undeclared identifiers."""
 27        super().enter_frame(frame)
 28
 29        for _, (action, param) in frame.symbols.loads.items():
 30            if action == "resolve" and param not in self.environment.globals:
 31                self.undeclared_identifiers.add(param)
 32
 33
 34def find_undeclared_variables(ast: nodes.Template) -> t.Set[str]:
 35    """Returns a set of all variables in the AST that will be looked up from
 36    the context at runtime.  Because at compile time it's not known which
 37    variables will be used depending on the path the execution takes at
 38    runtime, all variables are returned.
 39
 40    >>> from jinja2 import Environment, meta
 41    >>> env = Environment()
 42    >>> ast = env.parse('{% set foo = 42 %}{{ bar + foo }}')
 43    >>> meta.find_undeclared_variables(ast) == {'bar'}
 44    True
 45
 46    .. admonition:: Implementation
 47
 48       Internally the code generator is used for finding undeclared variables.
 49       This is good to know because the code generator might raise a
 50       :exc:`TemplateAssertionError` during compilation and as a matter of
 51       fact this function can currently raise that exception as well.
 52    """
 53    codegen = TrackingCodeGenerator(ast.environment)  # type: ignore
 54    codegen.visit(ast)
 55    return codegen.undeclared_identifiers
 56
 57
 58_ref_types = (nodes.Extends, nodes.FromImport, nodes.Import, nodes.Include)
 59_RefType = t.Union[nodes.Extends, nodes.FromImport, nodes.Import, nodes.Include]
 60
 61
 62def find_referenced_templates(ast: nodes.Template) -> t.Iterator[t.Optional[str]]:
 63    """Finds all the referenced templates from the AST.  This will return an
 64    iterator over all the hardcoded template extensions, inclusions and
 65    imports.  If dynamic inheritance or inclusion is used, `None` will be
 66    yielded.
 67
 68    >>> from jinja2 import Environment, meta
 69    >>> env = Environment()
 70    >>> ast = env.parse('{% extends "layout.html" %}{% include helper %}')
 71    >>> list(meta.find_referenced_templates(ast))
 72    ['layout.html', None]
 73
 74    This function is useful for dependency tracking.  For example if you want
 75    to rebuild parts of the website after a layout template has changed.
 76    """
 77    template_name: t.Any
 78
 79    for node in ast.find_all(_ref_types):
 80        template: nodes.Expr = node.template  # type: ignore
 81
 82        if not isinstance(template, nodes.Const):
 83            # a tuple with some non consts in there
 84            if isinstance(template, (nodes.Tuple, nodes.List)):
 85                for template_name in template.items:
 86                    # something const, only yield the strings and ignore
 87                    # non-string consts that really just make no sense
 88                    if isinstance(template_name, nodes.Const):
 89                        if isinstance(template_name.value, str):
 90                            yield template_name.value
 91                    # something dynamic in there
 92                    else:
 93                        yield None
 94            # something dynamic we don't know about here
 95            else:
 96                yield None
 97            continue
 98        # constant is a basestring, direct template name
 99        if isinstance(template.value, str):
100            yield template.value
101        # a tuple or list (latter *should* not happen) made of consts,
102        # yield the consts that are strings.  We could warn here for
103        # non string values
104        elif isinstance(node, nodes.Include) and isinstance(
105            template.value, (tuple, list)
106        ):
107            for template_name in template.value:
108                if isinstance(template_name, str):
109                    yield template_name
110        # something else we don't care about, we could warn here
111        else:
112            yield None