Initial implementation of local ID re-use when appending.

This commit adds to ID struct a new optional 'weak reference' to a
linked ID (in the form of a blend file library path and full ID name).

This can then be used on next append to try to find a matching local ID
instead of re-making the linked data local again.

Ref. T90545

NOTE: ID re-use will be disabled for regular append for the time being
(3.0 release), and only used for assets. Therefore, this commit should
not change anything user-wise.

Differential Revision: https://developer.blender.org/D12545

1 files changed, 202 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/main.c b/source/blender/blenkernel/intern/main.c
index 981f1d4a623..26dcadcc77b 100644
--- a/source/blender/blenkernel/intern/main.c
+++ b/source/blender/blenkernel/intern/main.c
@@ -35,6 +35,7 @@
 #include "DNA_ID.h"
 
 #include "BKE_global.h"
+#include "BKE_idtype.h"
 #include "BKE_lib_id.h"
 #include "BKE_lib_query.h"
 #include "BKE_main.h"
@@ -358,6 +359,207 @@ GSet *BKE_main_gset_create(Main *bmain, GSet *gset)
   return gset;
 }
 
+/* Utils for ID's library weak reference API. */
+typedef struct LibWeakRefKey {
+  char filepath[FILE_MAX];
+  char id_name[MAX_ID_NAME];
+} LibWeakRefKey;
+
+static LibWeakRefKey *lib_weak_key_create(LibWeakRefKey *key,
+                                          const char *lib_path,
+                                          const char *id_name)
+{
+  if (key == NULL) {
+    key = MEM_mallocN(sizeof(*key), __func__);
+  }
+  BLI_strncpy(key->filepath, lib_path, sizeof(key->filepath));
+  BLI_strncpy(key->id_name, id_name, sizeof(key->id_name));
+  return key;
+}
+
+static uint lib_weak_key_hash(const void *ptr)
+{
+  const LibWeakRefKey *string_pair = ptr;
+  uint hash = BLI_ghashutil_strhash_p_murmur(string_pair->filepath);
+  return hash ^ BLI_ghashutil_strhash_p_murmur(string_pair->id_name);
+}
+
+static bool lib_weak_key_cmp(const void *a, const void *b)
+{
+  const LibWeakRefKey *string_pair_a = a;
+  const LibWeakRefKey *string_pair_b = b;
+
+  return !(STREQ(string_pair_a->filepath, string_pair_b->filepath) &&
+           STREQ(string_pair_a->id_name, string_pair_b->id_name));
+}
+
+/**
+ * Generate a mapping between 'library path' of an ID (as a pair (relative blend file path, id
+ * name)), and a current local ID, if any.
+ *
+ * This uses the information stored in `ID.library_weak_reference`.
+ */
+GHash *BKE_main_library_weak_reference_create(Main *bmain)
+{
+  GHash *library_weak_reference_mapping = BLI_ghash_new(
+      lib_weak_key_hash, lib_weak_key_cmp, __func__);
+
+  ListBase *lb;
+  FOREACH_MAIN_LISTBASE_BEGIN (bmain, lb) {
+    ID *id_iter = lb->first;
+    if (id_iter == NULL) {
+      continue;
+    }
+    if (!BKE_idtype_idcode_append_is_reusable(GS(id_iter->name))) {
+      continue;
+    }
+    BLI_assert(BKE_idtype_idcode_is_linkable(GS(id_iter->name)));
+
+    FOREACH_MAIN_LISTBASE_ID_BEGIN (lb, id_iter) {
+      if (id_iter->library_weak_reference == NULL) {
+        continue;
+      }
+      LibWeakRefKey *key = lib_weak_key_create(NULL,
+                                               id_iter->library_weak_reference->library_filepath,
+                                               id_iter->library_weak_reference->library_id_name);
+      BLI_ghash_insert(library_weak_reference_mapping, key, id_iter);
+    }
+    FOREACH_MAIN_LISTBASE_ID_END;
+  }
+  FOREACH_MAIN_LISTBASE_END;
+
+  return library_weak_reference_mapping;
+}
+
+/**
+ * Destroy the data generated by #BKE_main_library_weak_reference_create.
+ */
+void BKE_main_library_weak_reference_destroy(GHash *library_weak_reference_mapping)
+{
+  BLI_ghash_free(library_weak_reference_mapping, MEM_freeN, NULL);
+}
+
+/**
+ * Search for a local ID matching the given linked ID reference.
+ *
+ * \param library_weak_reference_mapping: the mapping data generated by
+ * #BKE_main_library_weak_reference_create.
+ * \param library_relative_path: the path of a blend file library (relative to current working
+ * one).
+ * \param library_id_name: the full ID name, including the leading two chars encoding the ID
+ * type.
+ */
+ID *BKE_main_library_weak_reference_search_item(GHash *library_weak_reference_mapping,
+                                                const char *library_filepath,
+                                                const char *library_id_name)
+{
+  LibWeakRefKey key;
+  lib_weak_key_create(&key, library_filepath, library_id_name);
+  return (ID *)BLI_ghash_lookup(library_weak_reference_mapping, &key);
+}
+
+/**
+ * Add the given ID weak library reference to given local ID and the runtime mapping.
+ *
+ * \param library_weak_reference_mapping: the mapping data generated by
+ * #BKE_main_library_weak_reference_create.
+ * \param library_relative_path: the path of a blend file library (relative to current working
+ * one).
+ * \param library_id_name: the full ID name, including the leading two chars encoding the ID type.
+ * \param new_id: New local ID matching given weak reference.
+ */
+void BKE_main_library_weak_reference_add_item(GHash *library_weak_reference_mapping,
+                                              const char *library_filepath,
+                                              const char *library_id_name,
+                                              ID *new_id)
+{
+  BLI_assert(GS(library_id_name) == GS(new_id->name));
+  BLI_assert(new_id->library_weak_reference == NULL);
+  BLI_assert(BKE_idtype_idcode_append_is_reusable(GS(new_id->name)));
+
+  new_id->library_weak_reference = MEM_mallocN(sizeof(*(new_id->library_weak_reference)),
+                                               __func__);
+
+  LibWeakRefKey *key = lib_weak_key_create(NULL, library_filepath, library_id_name);
+  void **id_p;
+  const bool already_exist_in_mapping = BLI_ghash_ensure_p(
+      library_weak_reference_mapping, key, &id_p);
+  BLI_assert(!already_exist_in_mapping);
+
+  BLI_strncpy(new_id->library_weak_reference->library_filepath,
+              library_filepath,
+              sizeof(new_id->library_weak_reference->library_filepath));
+  BLI_strncpy(new_id->library_weak_reference->library_id_name,
+              library_id_name,
+              sizeof(new_id->library_weak_reference->library_id_name));
+  *id_p = new_id;
+}
+
+/**
+ * Update the status of the given ID weak library reference in current local IDs and the runtime
+ * mapping.
+ *
+ * This effectively transfers the 'ownership' of the given weak reference from `old_id` to
+ * `new_id`.
+ *
+ * \param library_weak_reference_mapping: the mapping data generated by
+ * #BKE_main_library_weak_reference_create.
+ * \param library_relative_path: the path of a blend file library (relative to current working
+ * one).
+ * \param library_id_name: the full ID name, including the leading two chars encoding the ID type.
+ * \param old_id: Existing local ID matching given weak reference.
+ * \param new_id: New local ID matching given weak reference.
+ */
+void BKE_main_library_weak_reference_update_item(GHash *library_weak_reference_mapping,
+                                                 const char *library_filepath,
+                                                 const char *library_id_name,
+                                                 ID *old_id,
+                                                 ID *new_id)
+{
+  BLI_assert(GS(library_id_name) == GS(old_id->name));
+  BLI_assert(GS(library_id_name) == GS(new_id->name));
+  BLI_assert(old_id->library_weak_reference != NULL);
+  BLI_assert(new_id->library_weak_reference == NULL);
+  BLI_assert(STREQ(old_id->library_weak_reference->library_filepath, library_filepath));
+  BLI_assert(STREQ(old_id->library_weak_reference->library_id_name, library_id_name));
+
+  LibWeakRefKey key;
+  lib_weak_key_create(&key, library_filepath, library_id_name);
+  void **id_p = BLI_ghash_lookup_p(library_weak_reference_mapping, &key);
+  BLI_assert(id_p != NULL && *id_p == old_id);
+
+  new_id->library_weak_reference = old_id->library_weak_reference;
+  old_id->library_weak_reference = NULL;
+  *id_p = new_id;
+}
+
+/**
+ * Remove the given ID weak library reference from the given local ID and the runtime mapping.
+ *
+ * \param library_weak_reference_mapping: the mapping data generated by
+ * #BKE_main_library_weak_reference_create.
+ * \param library_relative_path: the path of a blend file library (relative to current working
+ * one).
+ * \param library_id_name: the full ID name, including the leading two chars encoding the ID type.
+ * \param old_id: Existing local ID matching given weak reference.
+ */
+void BKE_main_library_weak_reference_remove_item(GHash *library_weak_reference_mapping,
+                                                 const char *library_filepath,
+                                                 const char *library_id_name,
+                                                 ID *old_id)
+{
+  BLI_assert(GS(library_id_name) == GS(old_id->name));
+  BLI_assert(old_id->library_weak_reference != NULL);
+
+  LibWeakRefKey key;
+  lib_weak_key_create(&key, library_filepath, library_id_name);
+
+  BLI_assert(BLI_ghash_lookup(library_weak_reference_mapping, &key) == old_id);
+  BLI_ghash_remove(library_weak_reference_mapping, &key, MEM_freeN, NULL);
+
+  MEM_SAFE_FREE(old_id->library_weak_reference);
+}
+
 /**
  * Generates a raw .blend file thumbnail data from given image.
  *