error when autogenerated IDs are used with persistence or snapshots

also give set_random_id a leading underscore so it doesn't
need to become a reserved word (disallowed prop name)

Author: alexcjohnson

dash/dependencies.py

@@ -30,7 +30,7 @@ class DashDependency:  # pylint: disable=too-few-public-methods
     def __init__(self, component_id, component_property):
 
         if isinstance(component_id, Component):
-            self.component_id = component_id.set_random_id()
+            self.component_id = component_id._set_random_id()
         else:
             self.component_id = component_id
 

dash/development/base_component.py

@@ -167,7 +167,29 @@ def __init__(self, **kwargs):
 
             setattr(self, k, v)
 
-    def set_random_id(self):
+    def _set_random_id(self):
+        if getattr(self, "persistence", False):
+            raise RuntimeError(
+                """
+                Attempting to use an auto-generated ID with the `persistence` prop.
+                This is prohibited because persistence is tied to component IDs and
+                auto-generated IDs can easily change.
+
+                Please assign an explicit ID to this component.
+            """
+            )
+        if "dash_snapshots" in sys.modules:
+            raise RuntimeError(
+                """
+                Attempting to use an auto-generated ID in an app with `dash_snapshots`.
+                This is prohibited because snapshots saves the whole app layout,
+                including component IDs, and auto-generated IDs can easily change.
+                Callbacks referencing the new IDs will not work old snapshots.
+
+                Please assign an explicit ID to this component.
+            """
+            )
+
         if not hasattr(self, "id"):
             v = str(uuid.UUID(int=rd.randint(0, 2 ** 128)))
             setattr(self, "id", v)

dash/development/component_generator.py

@@ -23,7 +23,6 @@
     "UNDEFINED",
     "REQUIRED",
     "to_plotly_json",
-    "set_random_id",
     "available_properties",
     "available_wildcard_properties",
     "_.*",

tests/unit/development/test_base_component.py

@@ -476,7 +476,7 @@ def test_debc027_component_error_message():
     )
 
 
-def test_set_random_id():
+def test_debc028_set_random_id():
     app = Dash(__name__)
 
     input1 = dcc.Input(value="Hello Input 1")
@@ -496,7 +496,7 @@ def update(v):
         return f"Input 2 {v}"
 
     @app.callback(
-        Output("output-3", "children"), Input(input1, "value"), Input(input2, "value")
+        Output(output3, "children"), Input(input1, "value"), Input(input2, "value")
     )
     def update(v1, v2):
         return f"Output 3 - Input 1: {v1}, Input 2: {v2}"
@@ -508,3 +508,21 @@ def update(v1, v2):
     assert input2.id == "23a7711a-8133-2876-37eb-dcd9e87a1613"
     # we make sure that the if the id is set explicitly, then it is not replaced by random id
     assert output3.id == "output-3"
+
+
+def test_debc029_random_id_errors():
+    app = Dash(__name__)
+
+    input1 = dcc.Input(value="Hello Input 1", persistence=True)
+    output1 = html.Div()
+
+    app.layout = html.Div([input1, output1])
+
+    with pytest.raises(RuntimeError) as e:
+
+        @app.callback(Output(output1, "children"), Input(input1, "value"))
+        def update(v):
+            return f"Input 1 {v}"
+
+    assert "persistence" in e.value.args[0]
+    assert "Please assign an explicit ID" in e.value.args[0]