Fix badly broken caches handling during undo/redo.

Original rework of caches during undo/redo (see D8183) had a very bad
flaw hidden in it: using the key of a ghash as source of data.

While this was effectively working then (cache pointer itself being part
of the key, and said cache pointers not being cleared on file write),
this is a general very bad way to do things.

Now that cache pointers are more and more cleared on file write (as part
of clearing runtime-data to reduce false-positives when checking if an
ID has changed or not), this has to be fixed properly by:
* Not storing the cache pointer itself in the IDCacheKey.
* In undo context, in readfile code trying to preserve caches, store the
  cache pointers as values of the mapping, together with the usages counter

The first change potentially affects all usages of
`BKE_idtype_id_foreach_cache`, but in practice this code is only used by
memfile reading code (i.e. undo) currently.

Related to T97015.

Reviewed By: brecht

Maniphest Tasks: T97015

Differential Revision: https://developer.blender.org/D14559

1 files changed, 24 insertions, 13 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 4ea6287399c..aba0bfe84d2 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -1689,12 +1689,14 @@ typedef struct BLOCacheStorage {
   MemArena *memarena;
 } BLOCacheStorage;
 
+typedef struct BLOCacheStorageValue {
+  void *cache_v;
+  uint new_usage_count;
+} BLOCacheStorageValue;
+
 /** Register a cache data entry to be preserved when reading some undo memfile. */
-static void blo_cache_storage_entry_register(ID *id,
-                                             const IDCacheKey *key,
-                                             void **UNUSED(cache_p),
-                                             uint UNUSED(flags),
-                                             void *cache_storage_v)
+static void blo_cache_storage_entry_register(
+    ID *id, const IDCacheKey *key, void **cache_p, uint UNUSED(flags), void *cache_storage_v)
 {
   BLI_assert(key->id_session_uuid == id->session_uuid);
   UNUSED_VARS_NDEBUG(id);
@@ -1704,7 +1706,11 @@ static void blo_cache_storage_entry_register(ID *id,
 
   IDCacheKey *storage_key = BLI_memarena_alloc(cache_storage->memarena, sizeof(*storage_key));
   *storage_key = *key;
-  BLI_ghash_insert(cache_storage->cache_map, storage_key, POINTER_FROM_UINT(0));
+  BLOCacheStorageValue *storage_value = BLI_memarena_alloc(cache_storage->memarena,
+                                                           sizeof(*storage_value));
+  storage_value->cache_v = *cache_p;
+  storage_value->new_usage_count = 0;
+  BLI_ghash_insert(cache_storage->cache_map, storage_key, storage_value);
 }
 
 /** Restore a cache data entry from old ID into new one, when reading some undo memfile. */
@@ -1723,13 +1729,13 @@ static void blo_cache_storage_entry_restore_in_new(
     return;
   }
 
-  void **value = BLI_ghash_lookup_p(cache_storage->cache_map, key);
-  if (value == NULL) {
+  BLOCacheStorageValue *storage_value = BLI_ghash_lookup(cache_storage->cache_map, key);
+  if (storage_value == NULL) {
     *cache_p = NULL;
     return;
   }
-  *value = POINTER_FROM_UINT(POINTER_AS_UINT(*value) + 1);
-  *cache_p = key->cache_v;
+  storage_value->new_usage_count++;
+  *cache_p = storage_value->cache_v;
 }
 
 /** Clear as needed a cache data entry from old ID, when reading some undo memfile. */
@@ -1741,14 +1747,19 @@ static void blo_cache_storage_entry_clear_in_old(ID *UNUSED(id),
 {
   BLOCacheStorage *cache_storage = cache_storage_v;
 
-  void **value = BLI_ghash_lookup_p(cache_storage->cache_map, key);
-  if (value == NULL) {
+  BLOCacheStorageValue *storage_value = BLI_ghash_lookup(cache_storage->cache_map, key);
+  if (storage_value == NULL) {
     *cache_p = NULL;
     return;
   }
   /* If that cache has been restored into some new ID, we want to remove it from old one, otherwise
    * keep it there so that it gets properly freed together with its ID. */
-  *cache_p = POINTER_AS_UINT(*value) != 0 ? NULL : key->cache_v;
+  if (storage_value->new_usage_count != 0) {
+    *cache_p = NULL;
+  }
+  else {
+    BLI_assert(*cache_p == storage_value->cache_v);
+  }
 }
 
 void blo_cache_storage_init(FileData *fd, Main *bmain)