[6.0.x] Fixed #36712 -- Evaluated type annotations lazily in template tag registration.

Ideally, this will be reverted when an upstream solution is available for
https://github.com/python/cpython/issues/141560.

Thanks Patrick Rauscher for the report and Augusto Pontes for the
first iteration and test.

Backport of 34186e731ca20a2344b1f88fd543a854d6b13a00 from main.

8 files changed, 138 insertions, 32 deletions

diff --git a/django/contrib/admin/templatetags/base.py b/django/contrib/admin/templatetags/base.py
index 9551c0e71d..3f8290d3b1 100644
--- a/django/contrib/admin/templatetags/base.py
+++ b/django/contrib/admin/templatetags/base.py
@@ -1,6 +1,7 @@
 from inspect import getfullargspec
 
 from django.template.library import InclusionNode, parse_bits
+from django.utils.inspect import lazy_annotations
 
 
 class InclusionAdminNode(InclusionNode):
@@ -11,9 +12,10 @@ class InclusionAdminNode(InclusionNode):
 
     def __init__(self, parser, token, func, template_name, takes_context=True):
         self.template_name = template_name
-        params, varargs, varkw, defaults, kwonly, kwonly_defaults, _ = getfullargspec(
-            func
-        )
+        with lazy_annotations():
+            params, varargs, varkw, defaults, kwonly, kwonly_defaults, _ = (
+                getfullargspec(func)
+            )
         bits = token.split_contents()
         args, kwargs = parse_bits(
             parser,
diff --git a/django/template/base.py b/django/template/base.py
index 5e541c3960..d6595e38e7 100644
--- a/django/template/base.py
+++ b/django/template/base.py
@@ -60,6 +60,7 @@ from django.template.context import BaseContext
 from django.utils.deprecation import django_file_prefixes
 from django.utils.formats import localize
 from django.utils.html import conditional_escape
+from django.utils.inspect import lazy_annotations
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.safestring import SafeData, SafeString, mark_safe
 from django.utils.text import get_text_list, smart_split, unescape_string_literal
@@ -825,7 +826,8 @@ class FilterExpression:
         # Check to see if a decorator is providing the real function.
         func = inspect.unwrap(func)
 
-        args, _, _, defaults, _, _, _ = inspect.getfullargspec(func)
+        with lazy_annotations():
+            args, _, _, defaults, _, _, _ = inspect.getfullargspec(func)
         alen = len(args)
         dlen = len(defaults or [])
         # Not enough OR Too many
diff --git a/django/template/library.py b/django/template/library.py
index 3fc4c5ebfc..27af7a6969 100644
--- a/django/template/library.py
+++ b/django/template/library.py
@@ -4,6 +4,7 @@ from importlib import import_module
 from inspect import getfullargspec, unwrap
 
 from django.utils.html import conditional_escape
+from django.utils.inspect import lazy_annotations
 
 from .base import Node, Template, token_kwargs
 from .exceptions import TemplateSyntaxError
@@ -110,15 +111,16 @@ class Library:
         """
 
         def dec(func):
-            (
-                params,
-                varargs,
-                varkw,
-                defaults,
-                kwonly,
-                kwonly_defaults,
-                _,
-            ) = getfullargspec(unwrap(func))
+            with lazy_annotations():
+                (
+                    params,
+                    varargs,
+                    varkw,
+                    defaults,
+                    kwonly,
+                    kwonly_defaults,
+                    _,
+                ) = getfullargspec(unwrap(func))
             function_name = name or func.__name__
 
             @wraps(func)
@@ -165,16 +167,16 @@ class Library:
 
         def dec(func):
             nonlocal end_name
-
-            (
-                params,
-                varargs,
-                varkw,
-                defaults,
-                kwonly,
-                kwonly_defaults,
-                _,
-            ) = getfullargspec(unwrap(func))
+            with lazy_annotations():
+                (
+                    params,
+                    varargs,
+                    varkw,
+                    defaults,
+                    kwonly,
+                    kwonly_defaults,
+                    _,
+                ) = getfullargspec(unwrap(func))
             function_name = name or func.__name__
 
             if end_name is None:
@@ -249,15 +251,16 @@ class Library:
         """
 
         def dec(func):
-            (
-                params,
-                varargs,
-                varkw,
-                defaults,
-                kwonly,
-                kwonly_defaults,
-                _,
-            ) = getfullargspec(unwrap(func))
+            with lazy_annotations():
+                (
+                    params,
+                    varargs,
+                    varkw,
+                    defaults,
+                    kwonly,
+                    kwonly_defaults,
+                    _,
+                ) = getfullargspec(unwrap(func))
             function_name = name or func.__name__
 
             @wraps(func)
diff --git a/django/utils/inspect.py b/django/utils/inspect.py
index ac5e82ca14..f0f43ae17e 100644
--- a/django/utils/inspect.py
+++ b/django/utils/inspect.py
@@ -1,11 +1,19 @@
 import functools
 import inspect
+import threading
+from contextlib import contextmanager
 
 from django.utils.version import PY314
 
 if PY314:
     import annotationlib
 
+    lock = threading.Lock()
+    safe_signature_from_callable = functools.partial(
+        inspect._signature_from_callable,
+        annotation_format=annotationlib.Format.FORWARDREF,
+    )
+
 
 @functools.lru_cache(maxsize=512)
 def _get_func_parameters(func, remove_first):
@@ -98,3 +106,27 @@ def is_module_level_function(func):
         return False
 
     return True
+
+
+@contextmanager
+def lazy_annotations():
+    """
+    inspect.getfullargspec eagerly evaluates type annotations. To add
+    compatibility with Python 3.14+ deferred evaluation, patch the module-level
+    helper to provide the annotation_format that we are using elsewhere.
+
+    This private helper could be removed when there is an upstream solution for
+    https://github.com/python/cpython/issues/141560.
+
+    This context manager is not reentrant.
+    """
+    if not PY314:
+        yield
+        return
+    with lock:
+        original_helper = inspect._signature_from_callable
+        inspect._signature_from_callable = safe_signature_from_callable
+        try:
+            yield
+        finally:
+            inspect._signature_from_callable = original_helper
diff --git a/docs/releases/5.2.9.txt b/docs/releases/5.2.9.txt
index 8a8000a9f1..9dfcc392a0 100644
--- a/docs/releases/5.2.9.txt
+++ b/docs/releases/5.2.9.txt
@@ -26,3 +26,7 @@ Bugfixes
   :class:`~django.http.HttpResponseRedirect` and
   :class:`~django.http.HttpResponsePermanentRedirect` for URLs longer than 2048
   characters. The limit is now 16384 characters (:ticket:`36743`).
+
+* Fixed a crash on Python 3.14+ that prevented template tag functions from
+  being registered when their type annotations required deferred evaluation
+  (:ticket:`36712`).
diff --git a/tests/admin_views/test_templatetags.py b/tests/admin_views/test_templatetags.py
index 185fe156a6..e8129cce1d 100644
--- a/tests/admin_views/test_templatetags.py
+++ b/tests/admin_views/test_templatetags.py
@@ -1,13 +1,17 @@
 import datetime
+import unittest
 
 from django.contrib.admin import ModelAdmin
 from django.contrib.admin.templatetags.admin_list import date_hierarchy
 from django.contrib.admin.templatetags.admin_modify import submit_row
+from django.contrib.admin.templatetags.base import InclusionAdminNode
 from django.contrib.auth import get_permission_codename
 from django.contrib.auth.admin import UserAdmin
 from django.contrib.auth.models import User
+from django.template.base import Token, TokenType
 from django.test import RequestFactory, TestCase
 from django.urls import reverse
+from django.utils.version import PY314
 
 from .admin import ArticleAdmin, site
 from .models import Article, Question
@@ -131,6 +135,22 @@ class AdminTemplateTagsTest(AdminViewBasicTestCase):
         self.assertContains(response, "override-pagination")
         self.assertContains(response, "override-search_form")
 
+    @unittest.skipUnless(PY314, "Deferred annotations are Python 3.14+ only")
+    def test_inclusion_admin_node_deferred_annotation(self):
+        def action(arg: SomeType = None):  # NOQA: F821
+            pass
+
+        # This used to raise TypeError via the underlying call to
+        # inspect.getfullargspec(), which is not ready for deferred
+        # evaluation of annotations.
+        InclusionAdminNode(
+            parser=object(),
+            token=Token(token_type=TokenType.TEXT, contents="a"),
+            func=action,
+            template_name="test.html",
+            takes_context=False,
+        )
+
 
 class DateHierarchyTests(TestCase):
     factory = RequestFactory()
diff --git a/tests/template_tests/test_library.py b/tests/template_tests/test_library.py
index 5827d33223..609b919923 100644
--- a/tests/template_tests/test_library.py
+++ b/tests/template_tests/test_library.py
@@ -1,8 +1,10 @@
 import functools
+import unittest
 
 from django.template import Library
 from django.template.base import Node
 from django.test import SimpleTestCase
+from django.utils.version import PY314
 
 
 class FilterRegistrationTests(SimpleTestCase):
@@ -78,6 +80,14 @@ class InclusionTagRegistrationTests(SimpleTestCase):
         self.assertIs(func_wrapped, func)
         self.assertTrue(hasattr(func_wrapped, "cache_info"))
 
+    @unittest.skipUnless(PY314, "Deferred annotations are Python 3.14+ only")
+    def test_inclusion_tag_deferred_annotation(self):
+        @self.library.inclusion_tag("template.html")
+        def func(arg: SomeType):  # NOQA: F821
+            return ""
+
+        self.assertIn("func", self.library.tags)
+
 
 class SimpleTagRegistrationTests(SimpleTestCase):
     def setUp(self):
@@ -104,6 +114,14 @@ class SimpleTagRegistrationTests(SimpleTestCase):
 
         self.assertIn("name", self.library.tags)
 
+    @unittest.skipUnless(PY314, "Deferred annotations are Python 3.14+ only")
+    def test_tag_deferred_annotation(self):
+        @self.library.simple_tag
+        def func(parser, token: SomeType):  # NOQA: F821
+            return Node()
+
+        self.assertIn("func", self.library.tags)
+
     def test_simple_tag_invalid(self):
         msg = "Invalid arguments provided to simple_tag"
         with self.assertRaisesMessage(ValueError, msg):
@@ -145,6 +163,14 @@ class SimpleBlockTagRegistrationTests(SimpleTestCase):
 
         self.assertIn("name", self.library.tags)
 
+    @unittest.skipUnless(PY314, "Deferred annotations are Python 3.14+ only")
+    def test_simple_block_tag_deferred_annotation(self):
+        @self.library.simple_block_tag
+        def func(content: SomeType):  # NOQA: F821
+            return content
+
+        self.assertIn("func", self.library.tags)
+
     def test_simple_block_tag_invalid(self):
         msg = "Invalid arguments provided to simple_block_tag"
         with self.assertRaisesMessage(ValueError, msg):
diff --git a/tests/template_tests/test_parser.py b/tests/template_tests/test_parser.py
index 317fb88238..9d68955b54 100644
--- a/tests/template_tests/test_parser.py
+++ b/tests/template_tests/test_parser.py
@@ -3,6 +3,8 @@ Testing some internals of the template processing.
 These are *not* examples to be copied in user code.
 """
 
+import unittest
+
 from django.template import Library, TemplateSyntaxError
 from django.template.base import (
     FilterExpression,
@@ -15,6 +17,7 @@ from django.template.base import (
 )
 from django.template.defaultfilters import register as filter_library
 from django.test import SimpleTestCase
+from django.utils.version import PY314
 
 
 class ParserTests(SimpleTestCase):
@@ -240,3 +243,17 @@ class ParserTests(SimpleTestCase):
                     FilterExpression(num, p).resolve({})
                 with self.assertRaises(TemplateSyntaxError):
                     FilterExpression(f"0|default:{num}", p).resolve({})
+
+    @unittest.skipUnless(PY314, "Deferred annotations are Python 3.14+ only")
+    def test_filter_deferred_annotation(self):
+        register = Library()
+
+        @register.filter("example")
+        def example_filter(value: str, arg: SomeType):  # NOQA: F821
+            return f"{value}_{arg}"
+
+        result = FilterExpression.args_check(
+            "example", example_filter, ["extra_example"]
+        )
+
+        self.assertIs(result, True)