use template_filter without parens

CHANGES.rst

@@ -5,6 +5,8 @@ Unreleased
 
 -   Drop support for Python 3.9. :pr:`5730`
 -   Remove previously deprecated code: ``__version__``. :pr:`5648`
+-   ``template_filter``, ``template_test``, and ``template_global`` decorators
+    can be used without parentheses. :issue:`5729`
 
 
 Version 3.1.1

docs/templating.rst

@@ -145,7 +145,11 @@ that.  You can either put them by hand into the
 :attr:`~flask.Flask.jinja_env` of the application or use the
 :meth:`~flask.Flask.template_filter` decorator.
 
-The two following examples work the same and both reverse an object::
+The following examples work the same and all reverse an object::
+
+    @app.template_filter # use the function name as filter name
+    def reverse_filter(s):
+        return s[::-1]
 
     @app.template_filter('reverse')
     def reverse_filter(s):

src/flask/sansio/app.py

@@ -662,8 +662,8 @@ class App(Scaffold):
 
     @setupmethod
     def template_filter(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_filter], T_template_filter]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_filter], T_template_filter] | T_template_filter:
         """A decorator that is used to register custom template filter.
         You can specify a name for the filter, otherwise the function
         name will be used. Example::
@@ -672,10 +672,26 @@ class App(Scaffold):
             def reverse(s):
                 return s[::-1]
 
+        The decorator also can be used without parentheses::
+
+            @app.template_filter
+            def reverse(s):
+                return s[::-1]
+
         :param name: the optional name of the filter, otherwise the
                      function name will be used.
         """
 
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @app.template_filter
+            # def func():
+
+            func = name
+            self.add_template_filter(func)
+            return func
+
         def decorator(f: T_template_filter) -> T_template_filter:
             self.add_template_filter(f, name=name)
             return f
@@ -696,8 +712,8 @@ class App(Scaffold):
 
     @setupmethod
     def template_test(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_test], T_template_test]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_test], T_template_test] | T_template_filter:
         """A decorator that is used to register custom template test.
         You can specify a name for the test, otherwise the function
         name will be used. Example::
@@ -711,12 +727,32 @@ class App(Scaffold):
                         return False
               return True
 
+        The decorator also can be used without parentheses::
+
+            @app.template_test
+            def is_prime(n):
+                if n == 2:
+                    return True
+                for i in range(2, int(math.ceil(math.sqrt(n))) + 1):
+                    if n % i == 0:
+                        return False
+
         .. versionadded:: 0.10
 
         :param name: the optional name of the test, otherwise the
                      function name will be used.
         """
 
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @app.template_test
+            # def func():
+
+            func = name
+            self.add_template_test(func)
+            return func
+
         def decorator(f: T_template_test) -> T_template_test:
             self.add_template_test(f, name=name)
             return f
@@ -739,8 +775,8 @@ class App(Scaffold):
 
     @setupmethod
     def template_global(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_global], T_template_global]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_global], T_template_global] | T_template_filter:
         """A decorator that is used to register a custom template global function.
         You can specify a name for the global function, otherwise the function
         name will be used. Example::
@@ -749,12 +785,28 @@ class App(Scaffold):
             def double(n):
                 return 2 * n
 
+        The decorator also can be used without parentheses::
+
+            @app.template_global
+            def double(n):
+                return 2 * n
+
         .. versionadded:: 0.10
 
         :param name: the optional name of the global function, otherwise the
                      function name will be used.
         """
 
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @app.template_global
+            # def func():
+
+            func = name
+            self.add_template_global(func)
+            return func
+
         def decorator(f: T_template_global) -> T_template_global:
             self.add_template_global(f, name=name)
             return f

src/flask/sansio/blueprints.py

@@ -442,8 +442,8 @@ class Blueprint(Scaffold):
 
     @setupmethod
     def app_template_filter(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_filter], T_template_filter]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_filter], T_template_filter] | T_template_filter:
         """Register a template filter, available in any template rendered by the
         application. Equivalent to :meth:`.Flask.template_filter`.
 
@@ -451,6 +451,16 @@ class Blueprint(Scaffold):
                      function name will be used.
         """
 
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @bp.add_template_filter
+            # def func():
+
+            func = name
+            self.add_app_template_filter(func)
+            return func
+
         def decorator(f: T_template_filter) -> T_template_filter:
             self.add_app_template_filter(f, name=name)
             return f
@@ -476,8 +486,8 @@ class Blueprint(Scaffold):
 
     @setupmethod
     def app_template_test(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_test], T_template_test]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_test], T_template_test] | T_template_filter:
         """Register a template test, available in any template rendered by the
         application. Equivalent to :meth:`.Flask.template_test`.
 
@@ -487,6 +497,16 @@ class Blueprint(Scaffold):
                      function name will be used.
         """
 
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @bp.add_template_test
+            # def func():
+
+            func = name
+            self.add_app_template_test(func)
+            return func
+
         def decorator(f: T_template_test) -> T_template_test:
             self.add_app_template_test(f, name=name)
             return f
@@ -514,8 +534,8 @@ class Blueprint(Scaffold):
 
     @setupmethod
     def app_template_global(
-        self, name: str | None = None
-    ) -> t.Callable[[T_template_global], T_template_global]:
+        self, name: t.Callable[..., t.Any] | str | None = None
+    ) -> t.Callable[[T_template_global], T_template_global] | T_template_filter:
         """Register a template global, available in any template rendered by the
         application. Equivalent to :meth:`.Flask.template_global`.
 
@@ -524,6 +544,15 @@ class Blueprint(Scaffold):
         :param name: the optional name of the global, otherwise the
                      function name will be used.
         """
+        if callable(name):
+            # If name is callable, it is the function to register.
+            # This is a shortcut for the common case of
+            # @bp.add_template_global
+            # def func():
+
+            func = name
+            self.add_app_template_global(func)
+            return func
 
         def decorator(f: T_template_global) -> T_template_global:
             self.add_app_template_global(f, name=name)

tests/test_blueprints.py

@@ -366,11 +366,35 @@ def test_template_filter(app):
     def my_reverse(s):
         return s[::-1]
 
+    @bp.app_template_filter
+    def my_reverse_2(s):
+        return s[::-1]
+
+    @bp.app_template_filter("my_reverse_custom_name_3")
+    def my_reverse_3(s):
+        return s[::-1]
+
+    @bp.app_template_filter(name="my_reverse_custom_name_4")
+    def my_reverse_4(s):
+        return s[::-1]
+
     app.register_blueprint(bp, url_prefix="/py")
     assert "my_reverse" in app.jinja_env.filters.keys()
     assert app.jinja_env.filters["my_reverse"] == my_reverse
     assert app.jinja_env.filters["my_reverse"]("abcd") == "dcba"
 
+    assert "my_reverse_2" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_2"] == my_reverse_2
+    assert app.jinja_env.filters["my_reverse_2"]("abcd") == "dcba"
+
+    assert "my_reverse_custom_name_3" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_custom_name_3"] == my_reverse_3
+    assert app.jinja_env.filters["my_reverse_custom_name_3"]("abcd") == "dcba"
+
+    assert "my_reverse_custom_name_4" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_custom_name_4"] == my_reverse_4
+    assert app.jinja_env.filters["my_reverse_custom_name_4"]("abcd") == "dcba"
+
 
 def test_add_template_filter(app):
     bp = flask.Blueprint("bp", __name__)
@@ -502,11 +526,35 @@ def test_template_test(app):
     def is_boolean(value):
         return isinstance(value, bool)
 
+    @bp.app_template_test
+    def boolean_2(value):
+        return isinstance(value, bool)
+
+    @bp.app_template_test("my_boolean_custom_name")
+    def boolean_3(value):
+        return isinstance(value, bool)
+
+    @bp.app_template_test(name="my_boolean_custom_name_2")
+    def boolean_4(value):
+        return isinstance(value, bool)
+
     app.register_blueprint(bp, url_prefix="/py")
     assert "is_boolean" in app.jinja_env.tests.keys()
     assert app.jinja_env.tests["is_boolean"] == is_boolean
     assert app.jinja_env.tests["is_boolean"](False)
 
+    assert "boolean_2" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["boolean_2"] == boolean_2
+    assert app.jinja_env.tests["boolean_2"](False)
+
+    assert "my_boolean_custom_name" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["my_boolean_custom_name"] == boolean_3
+    assert app.jinja_env.tests["my_boolean_custom_name"](False)
+
+    assert "my_boolean_custom_name_2" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["my_boolean_custom_name_2"] == boolean_4
+    assert app.jinja_env.tests["my_boolean_custom_name_2"](False)
+
 
 def test_add_template_test(app):
     bp = flask.Blueprint("bp", __name__)
@@ -679,6 +727,18 @@ def test_template_global(app):
     def get_answer():
         return 42
 
+    @bp.app_template_global
+    def get_stuff_1():
+        return "get_stuff_1"
+
+    @bp.app_template_global("my_get_stuff_custom_name_2")
+    def get_stuff_2():
+        return "get_stuff_2"
+
+    @bp.app_template_global(name="my_get_stuff_custom_name_3")
+    def get_stuff_3():
+        return "get_stuff_3"
+
     # Make sure the function is not in the jinja_env already
     assert "get_answer" not in app.jinja_env.globals.keys()
     app.register_blueprint(bp)
@@ -688,10 +748,31 @@ def test_template_global(app):
     assert app.jinja_env.globals["get_answer"] is get_answer
     assert app.jinja_env.globals["get_answer"]() == 42
 
+    assert "get_stuff_1" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["get_stuff_1"] == get_stuff_1
+    assert app.jinja_env.globals["get_stuff_1"](), "get_stuff_1"
+
+    assert "my_get_stuff_custom_name_2" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["my_get_stuff_custom_name_2"] == get_stuff_2
+    assert app.jinja_env.globals["my_get_stuff_custom_name_2"](), "get_stuff_2"
+
+    assert "my_get_stuff_custom_name_3" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["my_get_stuff_custom_name_3"] == get_stuff_3
+    assert app.jinja_env.globals["my_get_stuff_custom_name_3"](), "get_stuff_3"
+
     with app.app_context():
         rv = flask.render_template_string("{{ get_answer() }}")
         assert rv == "42"
 
+        rv = flask.render_template_string("{{ get_stuff_1() }}")
+        assert rv == "get_stuff_1"
+
+        rv = flask.render_template_string("{{ my_get_stuff_custom_name_2() }}")
+        assert rv == "get_stuff_2"
+
+        rv = flask.render_template_string("{{ my_get_stuff_custom_name_3() }}")
+        assert rv == "get_stuff_3"
+
 
 def test_request_processing(app, client):
     bp = flask.Blueprint("bp", __name__)

tests/test_templating.py

@@ -129,6 +129,30 @@ def test_template_filter(app):
     assert app.jinja_env.filters["my_reverse"] == my_reverse
     assert app.jinja_env.filters["my_reverse"]("abcd") == "dcba"
 
+    @app.template_filter
+    def my_reverse_2(s):
+        return s[::-1]
+
+    assert "my_reverse_2" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_2"] == my_reverse_2
+    assert app.jinja_env.filters["my_reverse_2"]("abcd") == "dcba"
+
+    @app.template_filter("my_reverse_custom_name_3")
+    def my_reverse_3(s):
+        return s[::-1]
+
+    assert "my_reverse_custom_name_3" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_custom_name_3"] == my_reverse_3
+    assert app.jinja_env.filters["my_reverse_custom_name_3"]("abcd") == "dcba"
+
+    @app.template_filter(name="my_reverse_custom_name_4")
+    def my_reverse_4(s):
+        return s[::-1]
+
+    assert "my_reverse_custom_name_4" in app.jinja_env.filters.keys()
+    assert app.jinja_env.filters["my_reverse_custom_name_4"] == my_reverse_4
+    assert app.jinja_env.filters["my_reverse_custom_name_4"]("abcd") == "dcba"
+
 
 def test_add_template_filter(app):
     def my_reverse(s):
@@ -223,6 +247,30 @@ def test_template_test(app):
     assert app.jinja_env.tests["boolean"] == boolean
     assert app.jinja_env.tests["boolean"](False)
 
+    @app.template_test
+    def boolean_2(value):
+        return isinstance(value, bool)
+
+    assert "boolean_2" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["boolean_2"] == boolean_2
+    assert app.jinja_env.tests["boolean_2"](False)
+
+    @app.template_test("my_boolean_custom_name")
+    def boolean_3(value):
+        return isinstance(value, bool)
+
+    assert "my_boolean_custom_name" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["my_boolean_custom_name"] == boolean_3
+    assert app.jinja_env.tests["my_boolean_custom_name"](False)
+
+    @app.template_test(name="my_boolean_custom_name_2")
+    def boolean_4(value):
+        return isinstance(value, bool)
+
+    assert "my_boolean_custom_name_2" in app.jinja_env.tests.keys()
+    assert app.jinja_env.tests["my_boolean_custom_name_2"] == boolean_4
+    assert app.jinja_env.tests["my_boolean_custom_name_2"](False)
+
 
 def test_add_template_test(app):
     def boolean(value):
@@ -320,6 +368,39 @@ def test_add_template_global(app, app_ctx):
     rv = flask.render_template_string("{{ get_stuff() }}")
     assert rv == "42"
 
+    @app.template_global
+    def get_stuff_1():
+        return "get_stuff_1"
+
+    assert "get_stuff_1" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["get_stuff_1"] == get_stuff_1
+    assert app.jinja_env.globals["get_stuff_1"](), "get_stuff_1"
+
+    rv = flask.render_template_string("{{ get_stuff_1() }}")
+    assert rv == "get_stuff_1"
+
+    @app.template_global("my_get_stuff_custom_name_2")
+    def get_stuff_2():
+        return "get_stuff_2"
+
+    assert "my_get_stuff_custom_name_2" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["my_get_stuff_custom_name_2"] == get_stuff_2
+    assert app.jinja_env.globals["my_get_stuff_custom_name_2"](), "get_stuff_2"
+
+    rv = flask.render_template_string("{{ my_get_stuff_custom_name_2() }}")
+    assert rv == "get_stuff_2"
+
+    @app.template_global(name="my_get_stuff_custom_name_3")
+    def get_stuff_3():
+        return "get_stuff_3"
+
+    assert "my_get_stuff_custom_name_3" in app.jinja_env.globals.keys()
+    assert app.jinja_env.globals["my_get_stuff_custom_name_3"] == get_stuff_3
+    assert app.jinja_env.globals["my_get_stuff_custom_name_3"](), "get_stuff_3"
+
+    rv = flask.render_template_string("{{ my_get_stuff_custom_name_3() }}")
+    assert rv == "get_stuff_3"
+
 
 def test_custom_template_loader(client):
     class MyFlask(flask.Flask):