LibOverrides: Refactor how diffing of RNA collections is handled.

Original implementation was a quick prototype which should have never
landed as-is in master. It had very limiting constraints and did not
allow for any real further development.

This commit fixes the internal implementation to make more sensible,
maintainable and evolutive.

NOTE: This commit introduces another forward-incompatibility in the
Blender file format: Files saved after this commit won't open properly
in older versions of blender regarding local inserted constraints or
modifiers into overrides of linked data.

NOTE: Technical details: The 'anchor' item name/index is now stored in
`subitem_reference_` members, and the actual 'source' item name/index is
stored in `subitem_local_` members of the override property operation
data.
Previously, only the `subitem_local_` members were used, storing the
anchor item name/index, and assuming the 'source' item was always the
next in the list.

Milestone I of T82160.

Maniphest Tasks: T82160

Differential Revision: https://developer.blender.org/D13282

1 files changed, 9 insertions, 20 deletions

diff --git a/source/blender/makesrna/intern/rna_pose.c b/source/blender/makesrna/intern/rna_pose.c
index cdf7fe5a7aa..87173adc38f 100644
--- a/source/blender/makesrna/intern/rna_pose.c
+++ b/source/blender/makesrna/intern/rna_pose.c
@@ -682,29 +682,18 @@ bool rna_PoseChannel_constraints_override_apply(Main *UNUSED(bmain),
   /* Remember that insertion operations are defined and stored in correct order, which means that
    * even if we insert several items in a row, we always insert first one, then second one, etc.
    * So we should always find 'anchor' constraint in both _src *and* _dst */
-  bConstraint *con_anchor = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    con_anchor = BLI_findstring(
-        &pchan_dst->constraints, opop->subitem_local_name, offsetof(bConstraint, name));
-  }
-  if (con_anchor == NULL && opop->subitem_local_index >= 0) {
-    con_anchor = BLI_findlink(&pchan_dst->constraints, opop->subitem_local_index);
-  }
-  /* Otherwise we just insert in first position. */
+  const size_t name_offset = offsetof(bConstraint, name);
+  bConstraint *con_anchor = BLI_listbase_string_or_index_find(&pchan_dst->constraints,
+                                                              opop->subitem_reference_name,
+                                                              name_offset,
+                                                              opop->subitem_reference_index);
+  /* If `con_anchor` is NULL, `con_src` will be inserted in first position. */
 
-  bConstraint *con_src = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    con_src = BLI_findstring(
-        &pchan_src->constraints, opop->subitem_local_name, offsetof(bConstraint, name));
-  }
-  if (con_src == NULL && opop->subitem_local_index >= 0) {
-    con_src = BLI_findlink(&pchan_src->constraints, opop->subitem_local_index);
-  }
-  con_src = con_src ? con_src->next : pchan_src->constraints.first;
+  bConstraint *con_src = BLI_listbase_string_or_index_find(
+      &pchan_src->constraints, opop->subitem_local_name, name_offset, opop->subitem_local_index);
 
   if (con_src == NULL) {
-    printf("%s: Could not find constraint to insert, doing nothing...\n", __func__);
-    BLI_assert(0);
+    BLI_assert(con_src != NULL);
     return false;
   }