Fix T72887: Outliner crashes when after undo of some linking operation.

Outliner tree building code was not handling properly empty libraries
(i.e. Lib datablocks in our bmain which have no used actual data
anymore).

Main issue here is unclean states of indirect hierarchies of linking
involving several libraries after undo operation.

This is not a critical issue though, just annoying and untidy.

1 files changed, 19 insertions, 15 deletions

diff --git a/source/blender/editors/space_outliner/outliner_tree.c b/source/blender/editors/space_outliner/outliner_tree.c
index ed0d85477f1..1bb1a1c5964 100644
--- a/source/blender/editors/space_outliner/outliner_tree.c
+++ b/source/blender/editors/space_outliner/outliner_tree.c
@@ -1267,6 +1267,7 @@ static TreeElement *outliner_add_library_contents(Main *mainvar,
   for (a = 0; a < tot; a++) {
     if (lbarray[a] && lbarray[a]->first) {
       ID *id = lbarray[a]->first;
+      const bool is_library = (GS(id->name) == ID_LI) && (lib != NULL);
 
       /* check if there's data in current lib */
       for (; id; id = id->next) {
@@ -1275,7 +1276,9 @@ static TreeElement *outliner_add_library_contents(Main *mainvar,
         }
       }
 
-      if (id) {
+      /* We always want to create an entry for libraries, even if/when we have no more IDs from
+       * them. This invalid state is important to show to user as well.*/
+      if (id != NULL || is_library) {
         if (!tenlib) {
           /* Create library tree element on demand, depending if there are any data-blocks. */
           if (lib) {
@@ -1288,18 +1291,20 @@ static TreeElement *outliner_add_library_contents(Main *mainvar,
         }
 
         /* Create data-block list parent element on demand. */
-        if (filter_id_type) {
-          ten = tenlib;
-        }
-        else {
-          ten = outliner_add_element(soops, &tenlib->subtree, lbarray[a], NULL, TSE_ID_BASE, 0);
-          ten->directdata = lbarray[a];
-          ten->name = outliner_idcode_to_plural(GS(id->name));
-        }
+        if (id != NULL) {
+          if (filter_id_type) {
+            ten = tenlib;
+          }
+          else {
+            ten = outliner_add_element(soops, &tenlib->subtree, lbarray[a], NULL, TSE_ID_BASE, 0);
+            ten->directdata = lbarray[a];
+            ten->name = outliner_idcode_to_plural(GS(id->name));
+          }
 
-        for (id = lbarray[a]->first; id; id = id->next) {
-          if (outliner_library_id_show(lib, id, filter_id_type)) {
-            outliner_add_element(soops, &ten->subtree, id, ten, 0, 0);
+          for (id = lbarray[a]->first; id; id = id->next) {
+            if (outliner_library_id_show(lib, id, filter_id_type)) {
+              outliner_add_element(soops, &ten->subtree, id, ten, 0, 0);
+            }
           }
         }
       }
@@ -2306,9 +2311,8 @@ void outliner_build_tree(
 
     for (lib = mainvar->libraries.first; lib; lib = lib->id.next) {
       ten = outliner_add_library_contents(mainvar, soops, &soops->tree, lib);
-      if (ten) {
-        lib->id.newid = (ID *)ten;
-      }
+      BLI_assert(ten != NULL);
+      lib->id.newid = (ID *)ten;
     }
     /* make hierarchy */
     ten = soops->tree.first;