Merge pull request #3157 from plotly/fix-hook-priority

Fix hook priority

Author: T4rk1n

dash/_hooks.py

@@ -71,10 +71,11 @@ def add_hook(
             return
         hks = self._ns.get(hook, [])
 
-        p = 0
+        p = priority or 0
         if not priority and len(hks):
-            priority_max = max(h.priority for h in hks)
-            p = priority_max - 1
+            # Take the minimum value and remove 1 to keep the order.
+            priority_min = min(h.priority for h in hks)
+            p = priority_min - 1
 
         hks.append(_Hook(func, priority=p, data=data))
         self._ns[hook] = sorted(hks, reverse=True, key=lambda h: h.priority)

tests/integration/test_hooks.py

@@ -114,24 +114,26 @@ def hook2(layout):
         layout.children.append(html.Div("second"))
         return layout
 
+    # This appears after the layout
+    @hooks.layout(priority=12)
+    def hook4(layout):
+        layout.children.append(html.Div("Prime"))
+        return layout
+
+    # Should still be last after setting a new max.
     @hooks.layout()
     def hook3(layout):
         layout.children.append(html.Div("third"))
         return layout
 
-    @hooks.layout(priority=6)
-    def hook4(layout):
-        layout.children.insert(0, html.Div("Prime"))
-        return layout
-
     app = Dash()
 
     app.layout = html.Div([html.Div("layout")], id="body")
 
     dash_duo.start_server(app)
     dash_duo.wait_for_text_to_equal("#final-wrapper > div:first-child", "final")
-    dash_duo.wait_for_text_to_equal("#body > div:first-child", "Prime")
-    dash_duo.wait_for_text_to_equal("#body > div:nth-child(2)", "layout")
+    dash_duo.wait_for_text_to_equal("#body > div:first-child", "layout")
+    dash_duo.wait_for_text_to_equal("#body > div:nth-child(2)", "Prime")
     dash_duo.wait_for_text_to_equal("#body > div:nth-child(3)", "first")
     dash_duo.wait_for_text_to_equal("#body > div:nth-child(4)", "second")
     dash_duo.wait_for_text_to_equal("#body > div:nth-child(5)", "third")