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/include/ED_file_indexer.h

@@ -0,0 +1,153 @@
+/*
+ * 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
+ */
+
+#pragma once
+
+#include "BLO_readfile.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * File indexing for the file/asset browser.
+ *
+ * This file contains an API to create indexing functionality when listing blend files in
+ * the file browser.
+ *
+ * To implement a custom indexer a `FileIndexerType` struct should be made and passed to the
+ * `filelist_setindexer` function.
+ */
+
+struct AssetLibraryReference;
+struct LinkNode;
+
+/**
+ * Result code of the `read_index` callback.
+ */
+typedef enum eFileIndexerResult {
+  /**
+   * File listing entries are loaded from the index. Reading entries from the blend file itself
+   * should be skipped.
+   */
+  FILE_INDEXER_ENTRIES_LOADED,
+
+  /**
+   * Index isn't available or not upto date. Entries should be read from te blend file and
+   * `update_index` must be called to update the index.
+   */
+  FILE_INDEXER_NEEDS_UPDATE,
+} eFileIndexerResult;
+
+/**
+ * FileIndexerEntry contains all data that is required to create a file listing entry.
+ */
+typedef struct FileIndexerEntry {
+  struct BLODataBlockInfo datablock_info;
+  short idcode;
+} FileIndexerEntry;
+
+/**
+ * Contains all entries of a blend file.
+ */
+typedef struct FileIndexerEntries {
+  struct LinkNode /* FileIndexerEntry */ *entries;
+} FileIndexerEntries;
+
+typedef void *(*FileIndexerInitUserDataFunc)(const char *root_directory,
+                                             size_t root_directory_maxlen);
+typedef void (*FileIndexerFreeUserDataFunc)(void *);
+typedef void (*FileIndexerFinishedFunc)(void *);
+typedef eFileIndexerResult (*FileIndexerReadIndexFunc)(const char *file_name,
+                                                       FileIndexerEntries *entries,
+                                                       int *r_read_entries_len,
+                                                       void *user_data);
+typedef void (*FileIndexerUpdateIndexFunc)(const char *file_name,
+                                           FileIndexerEntries *entries,
+                                           void *user_data);
+
+typedef struct FileIndexerType {
+  /**
+   * Is called at the beginning of the file listing process. An indexer can
+   * setup needed data. The result of this function will be passed around as `user_data` parameter.
+   *
+   * This is an optional callback.
+   */
+  FileIndexerInitUserDataFunc init_user_data;
+
+  /**
+   * Is called at the end of the file listing process. An indexer can free the data that it created
+   * during the file listing process.
+   *
+   * This is an optional callback */
+  FileIndexerFreeUserDataFunc free_user_data;
+
+  /**
+   * Is called at the end of the file listing process (before the `free_user_data`) where indexes
+   * can perform clean-ups.
+   *
+   * This is an optinal callback. Called when listing files completed.
+   */
+  FileIndexerFinishedFunc filelist_finished;
+
+  /**
+   * Is called for each blend file being listed to read data from the index.
+   *
+   * Read entries should be added to given `entries` parameter (type: `FileIndexerEntries`).
+   * `*r_read_entries_len` must be set to the number of read entries.
+   * and the function must return `eFileIndexerResult::FILE_INDEXER_ENTRIES_LOADED`.
+   * In this case the blend file will not be opened and the FileIndexerEntry added to `entries`
+   * will be used as the content of the file.
+   *
+   * When the index isn't available or could not be used no entries must be added to the
+   * entries field, `r_read_entries_len` must be set to `0` and the function must return
+   * `eFileIndexerResult::FILE_INDEXER_NEEDS_UPDATE`. In this case the blend file will read from
+   * the blend file and the `update_index` function will be called.
+   */
+  FileIndexerReadIndexFunc read_index;
+
+  /**
+   * Update an index of a blend file.
+   *
+   * Is called after reading entries from the file when the result of `read_index` was
+   * `eFileIndexerResult::FILE_INDEXER_NEED_UPDATE`. The callback should update the index so the
+   * next time that read_index is called it will read the entries from the index.
+   */
+  FileIndexerUpdateIndexFunc update_index;
+} FileIndexerType;
+
+/* file_indexer.cc */
+
+/** Removes all entries inside the given `indexer_entries`. */
+void ED_file_indexer_entries_clear(FileIndexerEntries *indexer_entries);
+
+/**
+ * Adds all entries from the given `datablock_infos` to the `indexer_entries`.
+ * The datablock_infos must only contain data for a single IDType. The specific IDType must be
+ * passed in the `idcode` parameter.
+ */
+void ED_file_indexer_entries_extend_from_datablock_infos(
+    FileIndexerEntries *indexer_entries,
+    const LinkNode * /* BLODataBlockInfo */ datablock_infos,
+    const int idcode);
+
+#ifdef __cplusplus
+}
+#endif