[mutter/wip/smcv/issue1414] input-mapper: Don't match touchscreens to the absence of a monitor

[Simon McVittie <smcv src gnome org>]

commit 32563869f92766cdd41db9de61dd42df2870ec68
Author: Simon McVittie <smcv debian org>
Date:   Wed Sep 9 10:15:32 2020 +0100

    input-mapper: Don't match touchscreens to the absence of a monitor
    
    If there is no laptop panel (for example on a desktop PC or a virtual
    machine), attempting to put a NULL monitor in the list of matches
    will just make mapping_helper_apply() crash.
    
    Mitigates: https://gitlab.gnome.org/GNOME/mutter/-/issues/1414
    Signed-off-by: Simon McVittie <smcv debian org>

 src/backends/meta-input-mapper.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/meta-input-mapper.c b/src/backends/meta-input-mapper.c
index 64be9f96a1..db85d0926e 100644
--- a/src/backends/meta-input-mapper.c
+++ b/src/backends/meta-input-mapper.c
@@ -367,6 +367,8 @@ guess_candidates (MetaInputMapper     *mapper,
       MetaOutputMatchType edid_match;
       DeviceMatch match = { l->data, 0 };
 
+      g_assert (META_IS_MONITOR (l->data));
+
       if (match_edid (input, l->data, &edid_match))
         match.score |= 1 << edid_match;
 
@@ -386,7 +388,10 @@ guess_candidates (MetaInputMapper     *mapper,
 
       match.monitor =
         meta_monitor_manager_get_laptop_panel (mapper->monitor_manager);
-      g_array_append_val (info->matches, match);
+
+      if (match.monitor != NULL)
+        g_array_append_val (info->matches, match);
+
       info->best = 0;
     }
   else