Asset System: Prepare File Browser backend for the Asset Browser

The Asset Browser will be a sub-editor of the File Browser. This prepares the
File Browser code for that.

**File-Lists**
* Support loading assets with metadata read from external files into the
  file-list.
* New main based file-list type, for the "Current File" asset library.
* Refresh file-list when switching between browse modes or asset libraries.
* Support empty file-lists (asset library with no assets).
* Store file previews as icons, so scripts can reference them via icon-id. See
  previous commit.

**Space Data**
* Introduce "browse mode" to differeniate between file and asset browsing.
* Add `FileAssetSelectParams` to `SpaceFile`, with `FileSelectParams` as base.
  Makes sure data is separated between asset and file browsing when switching
  between them. The active params can be obtained through
  `ED_fileselect_get_active_params()`.
* `FileAssetSelectParams` stores the currently visible asset library ID.
* Introduce file history abstraction so file and asset browsing can keep a
  separate history (previous and next directories).

**General**
* Option to only show asset data-blocks while file browsing (not exposed here).
* Add "active_file" context member, so scripts can get and display info about
  the active file.
* Add "active_id" context member, so `ED_OT_lib_id_load_custom_preview` can set
  a custom ID preview. (Only for "Current File" asset library)
* Expose some of `FileDirEntry` in RNA as (non-editable). That way scripts can
  obtain name, preview icon and asset-data.

Part of the first Asset Browser milestone. Check the #asset_browser_milestone_1
project milestone on developer.blender.org.

Differential Revision: https://developer.blender.org/D9724

Reviewed by: Bastien Montagne

1 files changed, 1 insertions, 8 deletions

diff --git a/source/blender/editors/space_file/file_ops.c b/source/blender/editors/space_file/file_ops.c
index b98348307f3..8af84f65ced 100644
--- a/source/blender/editors/space_file/file_ops.c
+++ b/source/blender/editors/space_file/file_ops.c
@@ -930,6 +930,7 @@ void FILE_OT_select_all(wmOperatorType *ot)
 
 /* Note we could get rid of this one, but it's used by some addon so...
  * Does not hurt keeping it around for now. */
+/* TODO disallow bookmark editing in assets mode? */
 static int bookmark_select_exec(bContext *C, wmOperator *op)
 {
   Main *bmain = CTX_data_main(C);
@@ -1836,10 +1837,6 @@ static int file_previous_exec(bContext *C, wmOperator *UNUSED(op))
   FileSelectParams *params = ED_fileselect_get_active_params(sfile);
 
   if (params) {
-    if (!sfile->folders_next) {
-      sfile->folders_next = folderlist_new();
-    }
-
     folderlist_pushdir(sfile->folders_next, params->dir);
     folderlist_popdir(sfile->folders_prev, params->dir);
     folderlist_pushdir(sfile->folders_next, params->dir);
@@ -1874,10 +1871,6 @@ static int file_next_exec(bContext *C, wmOperator *UNUSED(unused))
   SpaceFile *sfile = CTX_wm_space_file(C);
   FileSelectParams *params = ED_fileselect_get_active_params(sfile);
   if (params) {
-    if (!sfile->folders_next) {
-      sfile->folders_next = folderlist_new();
-    }
-
     folderlist_pushdir(sfile->folders_prev, params->dir);
     folderlist_popdir(sfile->folders_next, params->dir);