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diff --git a/third_party/python/Jinja2/jinja2/meta.py b/third_party/python/Jinja2/jinja2/meta.py
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+"""Functions that expose information about templates that might be
+interesting for introspection.
+"""
+import typing as t
+
+from . import nodes
+from .compiler import CodeGenerator
+from .compiler import Frame
+
+if t.TYPE_CHECKING:
+    from .environment import Environment
+
+
+class TrackingCodeGenerator(CodeGenerator):
+    """We abuse the code generator for introspection."""
+
+    def __init__(self, environment: "Environment") -> None:
+        super().__init__(environment, "<introspection>", "<introspection>")
+        self.undeclared_identifiers: t.Set[str] = set()
+
+    def write(self, x: str) -> None:
+        """Don't write."""
+
+    def enter_frame(self, frame: Frame) -> None:
+        """Remember all undeclared identifiers."""
+        super().enter_frame(frame)
+
+        for _, (action, param) in frame.symbols.loads.items():
+            if action == "resolve" and param not in self.environment.globals:
+                self.undeclared_identifiers.add(param)
+
+
+def find_undeclared_variables(ast: nodes.Template) -> t.Set[str]:
+    """Returns a set of all variables in the AST that will be looked up from
+    the context at runtime.  Because at compile time it's not known which
+    variables will be used depending on the path the execution takes at
+    runtime, all variables are returned.
+
+    >>> from jinja2 import Environment, meta
+    >>> env = Environment()
+    >>> ast = env.parse('{% set foo = 42 %}{{ bar + foo }}')
+    >>> meta.find_undeclared_variables(ast) == {'bar'}
+    True
+
+    .. admonition:: Implementation
+
+       Internally the code generator is used for finding undeclared variables.
+       This is good to know because the code generator might raise a
+       :exc:`TemplateAssertionError` during compilation and as a matter of
+       fact this function can currently raise that exception as well.
+    """
+    codegen = TrackingCodeGenerator(ast.environment)  # type: ignore
+    codegen.visit(ast)
+    return codegen.undeclared_identifiers
+
+
+_ref_types = (nodes.Extends, nodes.FromImport, nodes.Import, nodes.Include)
+_RefType = t.Union[nodes.Extends, nodes.FromImport, nodes.Import, nodes.Include]
+
+
+def find_referenced_templates(ast: nodes.Template) -> t.Iterator[t.Optional[str]]:
+    """Finds all the referenced templates from the AST.  This will return an
+    iterator over all the hardcoded template extensions, inclusions and
+    imports.  If dynamic inheritance or inclusion is used, `None` will be
+    yielded.
+
+    >>> from jinja2 import Environment, meta
+    >>> env = Environment()
+    >>> ast = env.parse('{% extends "layout.html" %}{% include helper %}')
+    >>> list(meta.find_referenced_templates(ast))
+    ['layout.html', None]
+
+    This function is useful for dependency tracking.  For example if you want
+    to rebuild parts of the website after a layout template has changed.
+    """
+    template_name: t.Any
+
+    for node in ast.find_all(_ref_types):
+        template: nodes.Expr = node.template  # type: ignore
+
+        if not isinstance(template, nodes.Const):
+            # a tuple with some non consts in there
+            if isinstance(template, (nodes.Tuple, nodes.List)):
+                for template_name in template.items:
+                    # something const, only yield the strings and ignore
+                    # non-string consts that really just make no sense
+                    if isinstance(template_name, nodes.Const):
+                        if isinstance(template_name.value, str):
+                            yield template_name.value
+                    # something dynamic in there
+                    else:
+                        yield None
+            # something dynamic we don't know about here
+            else:
+                yield None
+            continue
+        # constant is a basestring, direct template name
+        if isinstance(template.value, str):
+            yield template.value
+        # a tuple or list (latter *should* not happen) made of consts,
+        # yield the consts that are strings.  We could warn here for
+        # non string values
+        elif isinstance(node, nodes.Include) and isinstance(
+            template.value, (tuple, list)
+        ):
+            for template_name in template.value:
+                if isinstance(template_name, str):
+                    yield template_name
+        # something else we don't care about, we could warn here
+        else:
+            yield None