fix plotly#1223 - initialcall on new layout chunk edge case

Author: alexcjohnson

dash-renderer/src/actions/dependencies.js

@@ -1209,10 +1209,14 @@ export function getCallbacksInLayout(graphs, paths, layoutChunk, opts) {
         if (callback) {
             const foundIndex = foundCbIds[callback.resolvedId];
             if (foundIndex !== undefined) {
-                callbacks[foundIndex].changedPropIds = mergeMax(
-                    callbacks[foundIndex].changedPropIds,
+                const foundCb = callbacks[foundIndex];
+                foundCb.changedPropIds = mergeMax(
+                    foundCb.changedPropIds,
                     callback.changedPropIds
                 );
+                if (callback.initialCall) {
+                    foundCb.initialCall = true;
+                }
             } else {
                 foundCbIds[callback.resolvedId] = callbacks.length;
                 callbacks.push(callback);

tests/integration/callbacks/test_multiple_callbacks.py

@@ -262,3 +262,43 @@ def on_click(n_clicks):
     dash_duo.wait_for_text_to_equal("#output", "1")
     dash_duo.find_element("#btn").click()
     dash_duo.wait_for_text_to_equal("#output", "2")
+
+
+def test_cbmt007_early_preventupdate_inputs_above_below(dash_duo):
+    app = dash.Dash(__name__, suppress_callback_exceptions=True)
+    app.layout = html.Div(id="content")
+
+    @app.callback(Output("content", "children"), [Input("content", "style")])
+    def content(_):
+        return html.Div([
+            html.Div(42, id="above-in"),
+            html.Div(id="above-dummy"),
+            html.Hr(),
+            html.Div(0, id='above-out'),
+            html.Div(0, id='below-out'),
+            html.Hr(),
+            html.Div(id="below-dummy"),
+            html.Div(44, id="below-in"),
+        ])
+
+    # Create 4 callbacks - 2 above, 2 below.
+    for pos in ('above', 'below'):
+        @app.callback(
+            Output("{}-dummy".format(pos), "children"),
+            [Input("{}-dummy".format(pos), "style")]
+        )
+        def dummy(_):
+            raise PreventUpdate
+
+        @app.callback(
+            Output('{}-out'.format(pos), 'children'),
+            [Input('{}-in'.format(pos), 'children')]
+        )
+        def out(v):
+            return v
+
+    dash_duo.start_server(app)
+
+    # as of https://github.com/plotly/dash/issues/1223, above-out would be 0
+    dash_duo.wait_for_text_to_equal("#above-out", "42")
+    dash_duo.wait_for_text_to_equal("#below-out", "44")