1 files changed, 21 insertions, 17 deletions

diff --git a/source/blender/blenkernel/intern/blendfile.c b/source/blender/blenkernel/intern/blendfile.c
index efab2039dc3..3890bf4e7f8 100644
--- a/source/blender/blenkernel/intern/blendfile.c
+++ b/source/blender/blenkernel/intern/blendfile.c
@@ -134,26 +134,29 @@ static void setup_app_userdef(BlendFileData *bfd)
 static void setup_app_data(bContext *C,
                            BlendFileData *bfd,
                            const char *filepath,
-                           const bool is_startup,
+                           const struct BlendFileReadParams *params,
                            ReportList *reports)
 {
   Main *bmain = G_MAIN;
   Scene *curscene = NULL;
   const bool recover = (G.fileflags & G_FILE_RECOVER) != 0;
+  const bool is_startup = params->is_startup;
   enum {
     LOAD_UI = 1,
     LOAD_UI_OFF,
     LOAD_UNDO,
   } mode;
 
-  /* may happen with library files - UNDO file should never have NULL cursccene... */
-  if (ELEM(NULL, bfd->curscreen, bfd->curscene)) {
+  if (params->undo_direction != 0) {
+    BLI_assert(bfd->curscene != NULL);
+    mode = LOAD_UNDO;
+  }
+  /* may happen with library files - UNDO file should never have NULL curscene (but may have a
+   * NULL curscreen)... */
+  else if (ELEM(NULL, bfd->curscreen, bfd->curscene)) {
     BKE_report(reports, RPT_WARNING, "Library file, loading empty scene");
     mode = LOAD_UI_OFF;
   }
-  else if (BLI_listbase_is_empty(&bfd->main->screens)) {
-    mode = LOAD_UNDO;
-  }
   else if (G.fileflags & G_FILE_NO_UI) {
     mode = LOAD_UI_OFF;
   }
@@ -371,7 +374,9 @@ static void setup_app_data(bContext *C,
      * means that we do not reset their user count, however we do increase that one when doing
      * lib_link on local IDs using linked ones.
      * There is no real way to predict amount of changes here, so we have to fully redo
-     * refcounting . */
+     * refcounting.
+     * Now that we re-use (and do not liblink in readfile.c) most local datablocks as well, we have
+     * to recompute refcount for all local IDs too. */
     BKE_main_id_refcount_recompute(bmain, false);
   }
 }
@@ -386,7 +391,7 @@ static void setup_app_blend_file_data(bContext *C,
     setup_app_userdef(bfd);
   }
   if ((params->skip_flags & BLO_READ_SKIP_DATA) == 0) {
-    setup_app_data(C, bfd, filepath, params->is_startup, reports);
+    setup_app_data(C, bfd, filepath, params, reports);
   }
 }
 
@@ -473,16 +478,15 @@ bool BKE_blendfile_read_from_memfile(bContext *C,
   Main *bmain = CTX_data_main(C);
   BlendFileData *bfd;
 
-  bfd = BLO_read_from_memfile(
-      bmain, BKE_main_blendfile_path(bmain), memfile, params->skip_flags, reports);
+  bfd = BLO_read_from_memfile(bmain, BKE_main_blendfile_path(bmain), memfile, params, reports);
   if (bfd) {
-    /* remove the unused screens and wm */
-    while (bfd->main->wm.first) {
-      BKE_id_free(bfd->main, bfd->main->wm.first);
-    }
-    while (bfd->main->screens.first) {
-      BKE_id_free(bfd->main, bfd->main->screens.first);
-    }
+    /* Removing the unused workspaces, screens and wm is useless here, setup_app_data will switch
+     * those lists with the ones from old bmain, which freeing is much more efficient than
+     * individual calls to `BKE_id_free()`.
+     * Further more, those are expected to be empty anyway with new memfile reading code. */
+    BLI_assert(BLI_listbase_is_empty(&bfd->main->wm));
+    BLI_assert(BLI_listbase_is_empty(&bfd->main->workspaces));
+    BLI_assert(BLI_listbase_is_empty(&bfd->main->screens));
 
     setup_app_blend_file_data(C, bfd, "<memory1>", params, reports);
     BLO_blendfiledata_free(bfd);