Add C++ mockup

These functions don't change their inputs, so they can be const,
which is a bit more intuitive  and clean to use for callers.

source/blender/blenkernel/BKE_lib_id.h

@@ -603,7 +603,7 @@ bool BKE_id_can_be_asset(const struct ID *id);
  * we should either cache that status info also in virtual override IDs, or address the
  * long-standing TODO of getting an efficient 'owner_id' access for all embedded ID types.
  */
-bool BKE_id_is_editable(struct Main *bmain, struct ID *id);
+bool BKE_id_is_editable(const struct Main *bmain, const struct ID *id);
 
 /**
  * Returns ordered list of data-blocks for display in the UI.

source/blender/blenkernel/BKE_lib_override.h

@@ -62,12 +62,12 @@ void BKE_lib_override_library_free(struct IDOverrideLibrary **override, bool do_
 /**
  * Check if given ID has some override rules that actually indicate the user edited it.
  */
-bool BKE_lib_override_library_is_user_edited(struct ID *id);
+bool BKE_lib_override_library_is_user_edited(const struct ID *id);
 
 /**
  * Check if given ID is a system override.
  */
-bool BKE_lib_override_library_is_system_defined(struct Main *bmain, struct ID *id);
+bool BKE_lib_override_library_is_system_defined(const struct Main *bmain, const struct ID *id);
 
 /**
  * Check if given ID is a leaf in its liboverride hierarchy (i.e. if it does not use any other
@@ -75,7 +75,7 @@ bool BKE_lib_override_library_is_system_defined(struct Main *bmain, struct ID *i
  *
  * NOTE: Embedded IDs of override IDs are not considered as leaves.
  */
-bool BKE_lib_override_library_is_hierarchy_leaf(struct Main *bmain, struct ID *id);
+bool BKE_lib_override_library_is_hierarchy_leaf(const struct Main *bmain, const struct ID *id);
 
 /**
  * Create an overridden local copy of linked reference.

source/blender/blenkernel/intern/lib_id.c

@@ -2161,7 +2161,7 @@ bool BKE_id_can_be_asset(const ID *id)
          BKE_idtype_idcode_is_linkable(GS(id->name));
 }
 
-bool BKE_id_is_editable(Main *bmain, ID *id)
+bool BKE_id_is_editable(const Main *bmain, const ID *id)
 {
   return !(ID_IS_LINKED(id) || BKE_lib_override_library_is_system_defined(bmain, id));
 }

source/blender/blenkernel/intern/lib_override.c

@@ -88,7 +88,9 @@ BLI_INLINE void lib_override_object_posemode_transfer(ID *id_dst, ID *id_src)
 }
 
 /** Get override data for a given ID. Needed because of our beloved shape keys snowflake. */
-BLI_INLINE IDOverrideLibrary *lib_override_get(Main *bmain, ID *id, ID **r_owner_id)
+BLI_INLINE const IDOverrideLibrary *lib_override_get(const Main *bmain,
+                                                     const ID *id,
+                                                     const ID **r_owner_id)
 {
   if (r_owner_id != NULL) {
     *r_owner_id = id;
@@ -107,6 +109,12 @@ BLI_INLINE IDOverrideLibrary *lib_override_get(Main *bmain, ID *id, ID **r_owner
   return id->override_library;
 }
 
+BLI_INLINE IDOverrideLibrary *lib_override_get(Main *bmain, ID *id, ID **r_owner_id)
+{
+  return const_cast<IDOverrideLibrary *>(
+      lib_override_get(bmain, id, const_cast<ID **>(r_owner_id)));
+}
+
 IDOverrideLibrary *BKE_lib_override_library_init(ID *local_id, ID *reference_id)
 {
   /* If reference_id is NULL, we are creating an override template for purely local data.
@@ -264,7 +272,7 @@ static ID *lib_override_library_create_from(Main *bmain,
 
 /* TODO: This could be simplified by storing a flag in #IDOverrideLibrary
  * during the diffing process? */
-bool BKE_lib_override_library_is_user_edited(struct ID *id)
+bool BKE_lib_override_library_is_user_edited(const ID *id)
 {
 
   if (!ID_IS_OVERRIDE_LIBRARY(id)) {
@@ -278,8 +286,8 @@ bool BKE_lib_override_library_is_user_edited(struct ID *id)
     return false;
   }
 
-  LISTBASE_FOREACH (IDOverrideLibraryProperty *, op, &id->override_library->properties) {
-    LISTBASE_FOREACH (IDOverrideLibraryPropertyOperation *, opop, &op->operations) {
+  LISTBASE_FOREACH (const IDOverrideLibraryProperty *, op, &id->override_library->properties) {
+    LISTBASE_FOREACH (const IDOverrideLibraryPropertyOperation *, opop, &op->operations) {
       if ((opop->flag & IDOVERRIDE_LIBRARY_FLAG_IDPOINTER_MATCH_REFERENCE) != 0) {
         continue;
       }
@@ -294,11 +302,12 @@ bool BKE_lib_override_library_is_user_edited(struct ID *id)
   return false;
 }
 
-bool BKE_lib_override_library_is_system_defined(Main *bmain, ID *id)
+bool BKE_lib_override_library_is_system_defined(const Main *bmain, const ID *id)
 {
 
   if (ID_IS_OVERRIDE_LIBRARY(id)) {
-    ID *override_owner_id;
+    const ID *override_owner_id;
+    /* Cast away const, since the data is not changed. */
     lib_override_get(bmain, id, &override_owner_id);
     return (override_owner_id->override_library->flag & IDOVERRIDE_LIBRARY_FLAG_SYSTEM_DEFINED) !=
            0;
@@ -320,7 +329,7 @@ static int foreachid_is_hierarchy_leaf_fn(LibraryIDLinkCallbackData *cb_data)
   return IDWALK_RET_NOP;
 }
 
-bool BKE_lib_override_library_is_hierarchy_leaf(Main *bmain, ID *id)
+bool BKE_lib_override_library_is_hierarchy_leaf(const Main *bmain, const ID *id)
 {
   if (ID_IS_OVERRIDE_LIBRARY_REAL(id)) {
     bool is_leaf = true;
@@ -949,8 +958,8 @@ static void lib_override_overrides_group_tag_recursive(LibOverrideGroupTagData *
       continue;
     }
 
-    Library *reference_lib = lib_override_get(bmain, id_owner, NULL)->reference->lib;
-    ID *to_id_reference = lib_override_get(bmain, to_id, NULL)->reference;
+    const Library *reference_lib = lib_override_get(bmain, id_owner, NULL)->reference->lib;
+    const ID *to_id_reference = lib_override_get(bmain, to_id, NULL)->reference;
     if (to_id_reference->lib != reference_lib) {
       /* We do not override data-blocks from other libraries, nor do we process them. */
       continue;
@@ -1273,7 +1282,7 @@ static ID *lib_override_root_find(Main *bmain, ID *id, const int curr_level, int
     }
 
     BLI_assert(id->flag & LIB_EMBEDDED_DATA_LIB_OVERRIDE);
-    ID *id_owner;
+    const ID *id_owner;
     int best_level_placeholder = 0;
     lib_override_get(bmain, id, &id_owner);
     return lib_override_root_find(bmain, id_owner, curr_level + 1, &best_level_placeholder);