From 6de4b8d39e942957fdb482e395056e0c16fd0f2c Mon Sep 17 00:00:00 2001
From: Ian MacDougall Murray <i-murray@users.noreply.github.com>
Date: Wed, 4 Mar 2026 17:35:06 +0000
Subject: [PATCH 1/2] fix: flatten outputs before building loadingOutputs

Fixes #3619
---
 dash/dash-renderer/src/actions/callbacks.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/dash/dash-renderer/src/actions/callbacks.ts b/dash/dash-renderer/src/actions/callbacks.ts
index ee3a251378..37aab3f194 100644
--- a/dash/dash-renderer/src/actions/callbacks.ts
+++ b/dash/dash-renderer/src/actions/callbacks.ts
@@ -791,7 +791,7 @@ export function executeCallback(
         }
 
         const __execute = async (): Promise<CallbackResult> => {
-            const loadingOutputs = outputs.map(out => ({
+            const loadingOutputs = flatten(outputs).map(out => ({
                 path: getPath(paths, out.id),
                 property: out.property?.split('@')[0],
                 id: stringifyId(out.id)

From bebfe63f0a10b69db011708ee1d060b1b19189ec Mon Sep 17 00:00:00 2001
From: Ian MacDougall Murray <i-murray@users.noreply.github.com>
Date: Tue, 17 Mar 2026 21:11:16 +0000
Subject: [PATCH 2/2] test: add test for loading spinner with ALL wildcard
 pattern matching

Add test_ldcp019_loading_component_pattern_matching to verify that
dcc.Loading spinner triggers correctly when callback Output uses
the ALL wildcard with pattern-matching IDs.
---
 .../loading/test_loading_component.py         | 53 ++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/components/dash-core-components/tests/integration/loading/test_loading_component.py b/components/dash-core-components/tests/integration/loading/test_loading_component.py
index 35507dfe8a..261094965a 100644
--- a/components/dash-core-components/tests/integration/loading/test_loading_component.py
+++ b/components/dash-core-components/tests/integration/loading/test_loading_component.py
@@ -1,5 +1,5 @@
 from multiprocessing import Lock
-from dash import Dash, Input, Output, dcc, html
+from dash import Dash, Input, Output, dcc, html, MATCH, ALL
 from dash.dependencies import stringify_id
 from dash.testing import wait
 import time
@@ -839,3 +839,54 @@ def update_btn1_children(n_clicks):
     assert spinners == []
 
     assert dash_dcc.get_logs() == []
+
+
+# loading spinner triggers when callback Output uses ALL wildcard
+def test_ldcp019_loading_component_pattern_matching(dash_dcc):
+    lock = Lock()
+
+    app = Dash(__name__)
+
+    app.layout = html.Div(
+        [
+            dcc.Loading(
+                [
+                    html.Div(
+                        id={"type": "div-1", "index": 1, "name": "test"},
+                        className="div-1",
+                    )
+                ],
+                className="loading",
+            )
+        ],
+        id={"type": "root", "index": 1, "name": "test"},
+        className="root",
+    )
+
+    @app.callback(
+        Output(
+            {"type": "div-1", "index": ALL, "name": MATCH}, "children"
+        ),
+        Input(
+            {"type": "root", "index": ALL, "name": MATCH}, "n_clicks"
+        ),
+    )
+    def updateDiv(n_clicks):
+        if n_clicks == [1]:
+            time.sleep(0.1)
+            return ["changed"]
+        return ["content"]
+
+    with lock:
+        dash_dcc.start_server(app)
+        dash_dcc.wait_for_text_to_equal(".div-1", "content")
+
+        dash_dcc.find_element(".root").click()
+
+        dash_dcc.find_element(".loading .dash-spinner")
+        # mounted but hidden, so looks like no text
+        dash_dcc.wait_for_text_to_equal(".div-1", "")
+
+    dash_dcc.wait_for_text_to_equal(".div-1", "changed")
+
+    assert dash_dcc.get_logs() == []