T91406: Asset Library Indexing

Asset library indexing would store indexes of asset files to speed up
asset library browsing.

* Indexes are read when they are up to date
** Index should exist
** Index last modify data should be later than the file it indexes
** Index version should match
* The index of a file containing no assets can be load without opening
   the index file. The size of the file should be below a 32 bytes.
* Indexes are stored on a persistent cache folder.
* Unused index files are automatically removed.

The structure of the index files contains all data needed for browsing assets:
```
{
  "version": <file version number>,
  "entries": [{
    "name": "<asset name>",
    "catalog_id": "<catalog_id>",
    "catalog_name": "<catalog_name>",
    "description": "<description>",
    "author": "<author>",
    "tags": ["<tag>"]
  }]
}
```

Reviewed By: sybren, Severin

Maniphest Tasks: T91406

Differential Revision: https://developer.blender.org/D12693

source/blender/editors/space_file/file_indexer.cc

@@ -0,0 +1,96 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup edfile
+ *
+ * This file implements the default file browser indexer and has some helper function to work with
+ * `FileIndexerEntries`.
+ */
+#include "file_indexer.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "BLI_linklist.h"
+#include "BLI_listbase.h"
+#include "BLI_string.h"
+#include "BLI_utildefines.h"
+
+namespace blender::ed::file::indexer {
+
+static eFileIndexerResult read_index(const char *UNUSED(file_name),
+                                     FileIndexerEntries *UNUSED(entries),
+                                     int *UNUSED(r_read_entries_len),
+                                     void *UNUSED(user_data))
+{
+  return FILE_INDEXER_NEEDS_UPDATE;
+}
+
+static void update_index(const char *UNUSED(file_name),
+                         FileIndexerEntries *UNUSED(entries),
+                         void *UNUSED(user_data))
+{
+}
+
+constexpr FileIndexerType default_indexer()
+{
+  FileIndexerType indexer = {nullptr};
+  indexer.read_index = read_index;
+  indexer.update_index = update_index;
+  return indexer;
+}
+
+static FileIndexerEntry *file_indexer_entry_create_from_datablock_info(
+    const BLODataBlockInfo *datablock_info, const int idcode)
+{
+  FileIndexerEntry *entry = static_cast<FileIndexerEntry *>(
+      MEM_mallocN(sizeof(FileIndexerEntry), __func__));
+  entry->datablock_info = *datablock_info;
+  entry->idcode = idcode;
+  return entry;
+}
+
+}  // namespace blender::ed::file::indexer
+
+extern "C" {
+
+void ED_file_indexer_entries_extend_from_datablock_infos(
+    FileIndexerEntries *indexer_entries,
+    const LinkNode * /* BLODataBlockInfo */ datablock_infos,
+    const int idcode)
+{
+  for (const LinkNode *ln = datablock_infos; ln; ln = ln->next) {
+    const BLODataBlockInfo *datablock_info = static_cast<const BLODataBlockInfo *>(ln->link);
+    FileIndexerEntry *file_indexer_entry =
+        blender::ed::file::indexer::file_indexer_entry_create_from_datablock_info(datablock_info,
+                                                                                  idcode);
+    BLI_linklist_prepend(&indexer_entries->entries, file_indexer_entry);
+  }
+}
+
+static void ED_file_indexer_entry_free(void *indexer_entry)
+{
+  MEM_freeN(indexer_entry);
+}
+
+void ED_file_indexer_entries_clear(FileIndexerEntries *indexer_entries)
+{
+  BLI_linklist_free(indexer_entries->entries, ED_file_indexer_entry_free);
+  indexer_entries->entries = nullptr;
+}
+
+const FileIndexerType file_indexer_noop = blender::ed::file::indexer::default_indexer();
+}