Fix T77847: "Add plane > align" causes crash when certain rigs are in the scene (2.83, fixed in 2.90).

Root of the issue was not fixed in 2.90, only hidden by the fact that we
now re-read much less data during undo's that we used to, when some new
datablock gets added or removed.

This is not an ideal solution (as usual when dealing with data pointers
shared across data-blocks), but it's decent enough. thanks a lot to
@brecht for it!

To be backported to 2.83 too.

1 files changed, 15 insertions, 7 deletions

diff --git a/source/blender/blenloader/intern/writefile.c b/source/blender/blenloader/intern/writefile.c
index 0d1c3f2c3e5..6f9f3eec31d 100644
--- a/source/blender/blenloader/intern/writefile.c
+++ b/source/blender/blenloader/intern/writefile.c
@@ -152,6 +152,7 @@
 #include "MEM_guardedalloc.h"  // MEM_freeN
 
 #include "BKE_action.h"
+#include "BKE_armature.h"
 #include "BKE_blender_version.h"
 #include "BKE_bpath.h"
 #include "BKE_collection.h"
@@ -1582,7 +1583,7 @@ static void write_constraints(BlendWriter *writer, ListBase *conlist)
   }
 }
 
-static void write_pose(BlendWriter *writer, bPose *pose)
+static void write_pose(BlendWriter *writer, bPose *pose, bArmature *arm)
 {
   bPoseChannel *chan;
   bActionGroup *grp;
@@ -1592,6 +1593,8 @@ static void write_pose(BlendWriter *writer, bPose *pose)
     return;
   }
 
+  BLI_assert(arm != NULL);
+
   /* Write channels */
   for (chan = pose->chanbase.first; chan; chan = chan->next) {
     /* Write ID Properties -- and copy this comment EXACTLY for easy finding
@@ -1604,11 +1607,15 @@ static void write_pose(BlendWriter *writer, bPose *pose)
 
     write_motionpath(writer, chan->mpath);
 
-    /* prevent crashes with autosave,
-     * when a bone duplicated in editmode has not yet been assigned to its posechannel */
-    if (chan->bone) {
+    /* Prevent crashes with autosave,
+     * when a bone duplicated in editmode has not yet been assigned to its posechannel.
+     * Also needed with memundo, in some cases we can store a step before pose has been
+     * properly rebuilt from previous undo step. */
+    Bone *bone = (pose->flag & POSE_RECALC) ? BKE_armature_find_bone_name(arm, chan->name) :
+                                              chan->bone;
+    if (bone != NULL) {
       /* gets restored on read, for library armatures */
-      chan->selectflag = chan->bone->flag & BONE_SELECTED;
+      chan->selectflag = bone->flag & BONE_SELECTED;
     }
 
     BLO_write_struct(writer, bPoseChannel, chan);
@@ -1853,15 +1860,16 @@ static void write_object(BlendWriter *writer, Object *ob, const void *id_address
     BLO_write_pointer_array(writer, ob->totcol, ob->mat);
     BLO_write_raw(writer, sizeof(char) * ob->totcol, ob->matbits);
 
+    bArmature *arm = NULL;
     if (ob->type == OB_ARMATURE) {
-      bArmature *arm = ob->data;
+      arm = ob->data;
       if (arm && ob->pose && arm->act_bone) {
         BLI_strncpy(
             ob->pose->proxy_act_bone, arm->act_bone->name, sizeof(ob->pose->proxy_act_bone));
       }
     }
 
-    write_pose(writer, ob->pose);
+    write_pose(writer, ob->pose, arm);
     write_defgroups(writer, &ob->defbase);
     write_fmaps(writer, &ob->fmaps);
     write_constraints(writer, &ob->constraints);