Bugfix allow blueprints to be registered with a different name

This allows the same blueprint to be registered multiple times at the
same level, but with differing url_prefixes and names.

src/flask/blueprints.py

@@ -274,7 +274,8 @@ class Blueprint(Scaffold):
                 first_registration = False
 
         name_prefix = options.get("name_prefix", "")
-        name = f"{name_prefix}.{self.name}".lstrip(".")
+        self_name = options.get("name", self.name)
+        name = f"{name_prefix}.{self_name}".lstrip(".")
 
         if name in app.blueprints and app.blueprints[name] is not self:
             raise ValueError(

tests/test_blueprints.py

@@ -866,3 +866,16 @@ def test_nesting_url_prefixes(
 
     response = client.get("/parent/child/")
     assert response.status_code == 200
+
+
+def test_unique_blueprint_names(app, client) -> None:
+    bp = flask.Blueprint("bp", __name__)
+    bp2 = flask.Blueprint("bp", __name__)
+
+    app.register_blueprint(bp)
+    app.register_blueprint(bp)  # same name, same object, no error
+
+    with pytest.raises(ValueError):
+        app.register_blueprint(bp2)  # same name, different object
+
+    app.register_blueprint(bp2, name="alt")  # different name