[App] Fix bug when using structures with works

src/lightning_app/CHANGELOG.md

@@ -50,6 +50,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Fixed Sigterm Handler causing thread lock which caused KeyboardInterrupt to hang ([#15881](https://github.com/Lightning-AI/lightning/pull/15881))
 
+- Fixed a bug where using `L.app.structures` would cause multiple apps to be opened and fail with an error in the cloud ([#15911](https://github.com/Lightning-AI/lightning/pull/15911))
+
 
 ## [1.8.3] - 2022-11-22
 

src/lightning_app/structures/dict.py

@@ -64,10 +64,10 @@ def __setitem__(self, k, v):
         if isinstance(k, str) and "." in k:
             raise Exception(f"The provided name {k} contains . which is forbidden.")
 
+        _set_child_name(self, v, k)
         if self._backend:
             if isinstance(v, LightningFlow):
                 LightningFlow._attach_backend(v, self._backend)
-                _set_child_name(self, v, k)
             elif isinstance(v, LightningWork):
                 self._backend._wrap_run_method(_LightningAppRef().get_current(), v)
         v._name = f"{self.name}.{k}"

src/lightning_app/structures/list.py

@@ -55,20 +55,18 @@ def __init__(self, *items: T):
         self._backend: Optional[Backend] = None
         for item in items:
             self.append(item)
-            _set_child_name(self, item, str(self._last_index))
-            self._last_index += 1
 
     def append(self, v):
         from lightning_app import LightningFlow, LightningWork
 
+        _set_child_name(self, v, str(self._last_index))
         if self._backend:
             if isinstance(v, LightningFlow):
                 LightningFlow._attach_backend(v, self._backend)
-                _set_child_name(self, v, str(self._last_index))
             elif isinstance(v, LightningWork):
                 self._backend._wrap_run_method(_LightningAppRef().get_current(), v)
-            v._name = f"{self.name}.{self._last_index}"
-            self._last_index += 1
+        v._name = f"{self.name}.{self._last_index}"
+        self._last_index += 1
         super().append(v)
 
     @property

tests/tests_app/structures/test_structures.py

@@ -497,3 +497,25 @@ def test_structures_with_payload():
     app = LightningApp(FlowPayload(), log_level="debug")
     MultiProcessRuntime(app, start_server=False).dispatch()
     os.remove("payload")
+
+
+def test_structures_have_name_on_init():
+    """Test that the children in structures have the correct name assigned upon initialization."""
+
+    class ChildWork(LightningWork):
+        def run(self):
+            pass
+
+    class Collection(EmptyFlow):
+        def __init__(self):
+            super().__init__()
+            self.list_structure = List()
+            self.list_structure.append(ChildWork())
+
+            self.dict_structure = Dict()
+            self.dict_structure["dict_child"] = ChildWork()
+
+    flow = Collection()
+    LightningApp(flow)  # wrap in app to init all component names
+    assert flow.list_structure[0].name == "root.list_structure.0"
+    assert flow.dict_structure["dict_child"].name == "root.dict_structure.dict_child"