Resolve edge case in nested BP Groups (#2592)

sanic/app.py

@@ -480,15 +480,14 @@ class Sanic(BaseSanic, StartupMixin, metaclass=TouchUpMeta):
             for item in blueprint:
                 params = {**options}
                 if isinstance(blueprint, BlueprintGroup):
-                    if blueprint.url_prefix:
                     merge_from = [
                         options.get("url_prefix", ""),
-                            blueprint.url_prefix,
+                        blueprint.url_prefix or "",
                     ]
                     if not isinstance(item, BlueprintGroup):
                         merge_from.append(item.url_prefix or "")
                     merged_prefix = "/".join(
-                            u.strip("/") for u in merge_from
+                        u.strip("/") for u in merge_from if u
                     ).rstrip("/")
                     params["url_prefix"] = f"/{merged_prefix}"
 

tests/test_blueprint_group.py

@@ -323,3 +323,20 @@ def test_bp_group_properties():
     assert "api/v1/grouped/bp2/" in routes
     assert "api/v1/primary/grouped/bp1" in routes
     assert "api/v1/primary/grouped/bp2" in routes
+
+
+def test_nested_bp_group_properties():
+    one = Blueprint("one", url_prefix="/one")
+    two = Blueprint.group(one)
+    three = Blueprint.group(two, url_prefix="/three")
+
+    @one.route("/four")
+    def handler(request):
+        return text("pi")
+
+    app = Sanic("PropTest")
+    app.blueprint(three)
+    app.router.finalize()
+
+    routes = [route.path for route in app.router.routes]
+    assert routes == ["three/one/four"]