From 96404287bc4269dea7b037e7b178e54ebf616d47 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Tue, 24 Nov 2020 17:34:08 +0800
Subject: [PATCH] st-bin: Disallow st_bin_set_child with already-parented
 children

Not checking for this would result in `clutter_actor_add_child`
failing, but StBin keeping a copy in `priv->child`. So later on,
`st_bin_remove` would never be called on it and this assertion
would fail and crash the whole shell:

```
static void
st_bin_destroy (ClutterActor *actor)
{
  StBinPrivate *priv = st_bin_get_instance_private (ST_BIN (actor));

  if (priv->child)
    clutter_actor_destroy (priv->child);
  g_assert (priv->child == NULL);

```

By disallowing spurious `st_bin_set_child` calls we now prevent StBin
from entering such a corrupt state and the above assertion won't fail
anymore.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1507>
---
 src/st/st-bin.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/st/st-bin.c b/src/st/st-bin.c
index f013909e8..7959a4e95 100644
--- a/src/st/st-bin.c
+++ b/src/st/st-bin.c
@@ -434,6 +434,19 @@ st_bin_set_child (StBin        *bin,
   if (priv->child == child)
     return;
 
+  if (child)
+    {
+      ClutterActor *parent = clutter_actor_get_parent (child);
+
+      if (parent)
+        {
+          g_warning ("%s: The provided 'child' actor %p already has a "
+                     "(different) parent %p and can't be made a child of %p.",
+                     G_STRFUNC, child, parent, bin);
+          return;
+        }
+    }
+
   if (priv->child)
     clutter_actor_remove_child (CLUTTER_ACTOR (bin), priv->child);
 
-- 
2.38.1