blinker is required, signals are always available

src/flask/__init__.py

@@ -32,7 +32,6 @@ from .signals import message_flashed as message_flashed
 from .signals import request_finished as request_finished
 from .signals import request_started as request_started
 from .signals import request_tearing_down as request_tearing_down
-from .signals import signals_available as signals_available
 from .signals import template_rendered as template_rendered
 from .templating import render_template as render_template
 from .templating import render_template_string as render_template_string
@@ -89,4 +88,15 @@ def __getattr__(name):
         )
         return Markup
 
+    if name == "signals_available":
+        import warnings
+
+        warnings.warn(
+            "'signals_available' is deprecated and will be removed in Flask 2.4."
+            " Signals are always available",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return True
+
     raise AttributeError(name)

src/flask/signals.py

@@ -1,49 +1,13 @@
+from __future__ import annotations
+
 import typing as t
+import warnings
 
-try:
-    from blinker import Namespace
+from blinker import Namespace
 
-    signals_available = True
-except ImportError:
-    signals_available = False
-
-    class Namespace:  # type: ignore
-        def signal(self, name: str, doc: t.Optional[str] = None) -> "_FakeSignal":
-            return _FakeSignal(name, doc)
-
-    class _FakeSignal:
-        """If blinker is unavailable, create a fake class with the same
-        interface that allows sending of signals but will fail with an
-        error on anything else.  Instead of doing anything on send, it
-        will just ignore the arguments and do nothing instead.
-        """
-
-        def __init__(self, name: str, doc: t.Optional[str] = None) -> None:
-            self.name = name
-            self.__doc__ = doc
-
-        def send(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
-            pass
-
-        def _fail(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
-            raise RuntimeError(
-                "Signalling support is unavailable because the blinker"
-                " library is not installed."
-            ) from None
-
-        connect = connect_via = connected_to = temporarily_connected_to = _fail
-        disconnect = _fail
-        has_receivers_for = receivers_for = _fail
-        del _fail
-
-
-# The namespace for code signals.  If you are not Flask code, do
-# not put signals in here.  Create your own namespace instead.
+# This namespace is only for signals provided by Flask itself.
 _signals = Namespace()
 
-
-# Core signals.  For usage examples grep the source code or consult
-# the API documentation in docs/api.rst as well as docs/signals.rst
 template_rendered = _signals.signal("template-rendered")
 before_render_template = _signals.signal("before-render-template")
 request_started = _signals.signal("request-started")
@@ -54,3 +18,16 @@ appcontext_tearing_down = _signals.signal("appcontext-tearing-down")
 appcontext_pushed = _signals.signal("appcontext-pushed")
 appcontext_popped = _signals.signal("appcontext-popped")
 message_flashed = _signals.signal("message-flashed")
+
+
+def __getattr__(name: str) -> t.Any:
+    if name == "signals_available":
+        warnings.warn(
+            "The 'signals_available' attribute is deprecated and will be removed in"
+            " Flask 2.4. Signals are always available.",
+            DeprecationWarning,
+            stacklevel=2,
+        )
+        return True
+
+    raise AttributeError(name)