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

4 files changed, 56 insertions, 84 deletions

diff --git a/source/blender/makesrna/intern/rna_animation.c b/source/blender/makesrna/intern/rna_animation.c
index 52c25bae45a..9068fdb6e72 100644
--- a/source/blender/makesrna/intern/rna_animation.c
+++ b/source/blender/makesrna/intern/rna_animation.c
@@ -761,8 +761,8 @@ bool rna_NLA_tracks_override_apply(Main *bmain,
   /* This is not working so well with index-based insertion, especially in case some tracks get
    * added to lib linked data. So we simply add locale tracks at the end of the list always, order
    * of override operations should ensure order of local tracks is preserved properly. */
-  if (opop->subitem_local_index >= 0) {
-    nla_track_anchor = BLI_findlink(&anim_data_dst->nla_tracks, opop->subitem_local_index);
+  if (opop->subitem_reference_index >= 0) {
+    nla_track_anchor = BLI_findlink(&anim_data_dst->nla_tracks, opop->subitem_reference_index);
   }
   /* Otherwise we just insert in first position. */
 #  else
@@ -773,9 +773,11 @@ bool rna_NLA_tracks_override_apply(Main *bmain,
   if (opop->subitem_local_index >= 0) {
     nla_track_src = BLI_findlink(&anim_data_src->nla_tracks, opop->subitem_local_index);
   }
-  nla_track_src = nla_track_src ? nla_track_src->next : anim_data_src->nla_tracks.first;
 
-  BLI_assert(nla_track_src != NULL);
+  if (nla_track_src == NULL) {
+    BLI_assert(nla_track_src != NULL);
+    return false;
+  }
 
   NlaTrack *nla_track_dst = BKE_nlatrack_copy(bmain, nla_track_src, true, 0);
 
diff --git a/source/blender/makesrna/intern/rna_object.c b/source/blender/makesrna/intern/rna_object.c
index bf64196c8ab..0cb132786cd 100644
--- a/source/blender/makesrna/intern/rna_object.c
+++ b/source/blender/makesrna/intern/rna_object.c
@@ -1705,27 +1705,20 @@ bool rna_Object_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(
-        &ob_dst->constraints, opop->subitem_local_name, offsetof(bConstraint, name));
-  }
-  if (con_anchor == NULL && opop->subitem_local_index >= 0) {
-    con_anchor = BLI_findlink(&ob_dst->constraints, opop->subitem_local_index);
-  }
-  /* Otherwise we just insert in first position. */
-
-  bConstraint *con_src = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    con_src = BLI_findstring(
-        &ob_src->constraints, opop->subitem_local_name, offsetof(bConstraint, name));
-  }
-  if (con_src == NULL && opop->subitem_local_index >= 0) {
-    con_src = BLI_findlink(&ob_src->constraints, opop->subitem_local_index);
+  const size_t name_offset = offsetof(bConstraint, name);
+  bConstraint *con_anchor = BLI_listbase_string_or_index_find(&ob_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 = BLI_listbase_string_or_index_find(
+      &ob_src->constraints, opop->subitem_local_name, name_offset, opop->subitem_local_index);
+
+  if (con_src == NULL) {
+    BLI_assert(con_src != NULL);
+    return false;
   }
-  con_src = con_src ? con_src->next : ob_src->constraints.first;
-
-  BLI_assert(con_src != NULL);
 
   bConstraint *con_dst = BKE_constraint_duplicate_ex(con_src, 0, true);
 
@@ -1827,25 +1820,15 @@ bool rna_Object_modifiers_override_apply(Main *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' modifier in both _src *and* _dst. */
-  ModifierData *mod_anchor = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    mod_anchor = BLI_findstring(
-        &ob_dst->modifiers, opop->subitem_local_name, offsetof(ModifierData, name));
-  }
-  if (mod_anchor == NULL && opop->subitem_local_index >= 0) {
-    mod_anchor = BLI_findlink(&ob_dst->modifiers, opop->subitem_local_index);
-  }
-  /* Otherwise we just insert in first position. */
+  const size_t name_offset = offsetof(ModifierData, name);
+  ModifierData *mod_anchor = BLI_listbase_string_or_index_find(&ob_dst->modifiers,
+                                                               opop->subitem_reference_name,
+                                                               name_offset,
+                                                               opop->subitem_reference_index);
+  /* If `mod_anchor` is NULL, `mod_src` will be inserted in first position. */
 
-  ModifierData *mod_src = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    mod_src = BLI_findstring(
-        &ob_src->modifiers, opop->subitem_local_name, offsetof(ModifierData, name));
-  }
-  if (mod_src == NULL && opop->subitem_local_index >= 0) {
-    mod_src = BLI_findlink(&ob_src->modifiers, opop->subitem_local_index);
-  }
-  mod_src = mod_src ? mod_src->next : ob_src->modifiers.first;
+  ModifierData *mod_src = BLI_listbase_string_or_index_find(
+      &ob_src->modifiers, opop->subitem_local_name, name_offset, opop->subitem_local_index);
 
   if (mod_src == NULL) {
     BLI_assert(mod_src != NULL);
@@ -1934,25 +1917,18 @@ bool rna_Object_greasepencil_modifiers_override_apply(Main *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' modifier in both _src *and* _dst. */
-  GpencilModifierData *mod_anchor = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    mod_anchor = BLI_findstring(
-        &ob_dst->greasepencil_modifiers, opop->subitem_local_name, offsetof(ModifierData, name));
-  }
-  if (mod_anchor == NULL && opop->subitem_local_index >= 0) {
-    mod_anchor = BLI_findlink(&ob_dst->greasepencil_modifiers, opop->subitem_local_index);
-  }
-  /* Otherwise we just insert in first position. */
-
-  GpencilModifierData *mod_src = NULL;
-  if (opop->subitem_local_name && opop->subitem_local_name[0]) {
-    mod_src = BLI_findstring(
-        &ob_src->greasepencil_modifiers, opop->subitem_local_name, offsetof(ModifierData, name));
-  }
-  if (mod_src == NULL && opop->subitem_local_index >= 0) {
-    mod_src = BLI_findlink(&ob_src->greasepencil_modifiers, opop->subitem_local_index);
-  }
-  mod_src = mod_src ? mod_src->next : ob_src->greasepencil_modifiers.first;
+  const size_t name_offset = offsetof(GpencilModifierData, name);
+  GpencilModifierData *mod_anchor = BLI_listbase_string_or_index_find(
+      &ob_dst->greasepencil_modifiers,
+      opop->subitem_reference_name,
+      name_offset,
+      opop->subitem_reference_index);
+  /* If `mod_anchor` is NULL, `mod_src` will be inserted in first position. */
+
+  GpencilModifierData *mod_src = BLI_listbase_string_or_index_find(&ob_src->greasepencil_modifiers,
+                                                                   opop->subitem_local_name,
+                                                                   name_offset,
+                                                                   opop->subitem_local_index);
 
   if (mod_src == NULL) {
     BLI_assert(mod_src != NULL);
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;
   }
 
diff --git a/source/blender/makesrna/intern/rna_rna.c b/source/blender/makesrna/intern/rna_rna.c
index 12fb7a40d13..e5009305fe5 100644
--- a/source/blender/makesrna/intern/rna_rna.c
+++ b/source/blender/makesrna/intern/rna_rna.c
@@ -1916,16 +1916,21 @@ int rna_property_override_diff_default(Main *bmain,
 
           /* Collections do not support replacement of their data (except for collections of ID
            * pointers), since they do not support removing, only in *some* cases, insertion. We
-           * also assume then that _a data is the one where things are inserted. */
+           * also assume then that _a data is the one where things are inserted.
+           *
+           * NOTE: In insertion case, both 'local' and 'reference' (aka anchor) sub-item
+           * identifiers refer to collection items in the local override. The 'reference' may match
+           * an item in the linked reference data, but it can also be another local-only item added
+           * by a previous INSERT operation. */
           if (is_valid_for_insertion && use_collection_insertion) {
             op = BKE_lib_override_library_property_get(override, rna_path, &created);
 
             BKE_lib_override_library_property_operation_get(op,
                                                             IDOVERRIDE_LIBRARY_OP_INSERT_AFTER,
-                                                            NULL,
                                                             no_prop_name ? NULL : prev_propname_a,
-                                                            -1,
+                                                            no_prop_name ? NULL : propname_a,
                                                             idx_a - 1,
+                                                            idx_a,
                                                             true,
                                                             NULL,
                                                             NULL);