UI: Support defining UI lists in C

So far all UI lists had to be defined in Python, this makes it possible
to define them in C as well. Note that there is a whole bunch of special
handling for the Python API that isn't there for C. I think most
importantly custom properties support, which currently can't be added
for C defined UI lists.

The upcoming asset view UI template will use this, which needs to be
defined in C.

Adds a new file `interface_template_list.cc`, which at this point is
mostly a dummy to have a place for the `ED_uilisttypes_ui()` definition.
I plan a separate cleanup to move the UI-list template to that file.

3 files changed, 62 insertions, 3 deletions

diff --git a/source/blender/windowmanager/WM_api.h b/source/blender/windowmanager/WM_api.h
index c529fef73ef..66e91526009 100644
--- a/source/blender/windowmanager/WM_api.h
+++ b/source/blender/windowmanager/WM_api.h
@@ -618,7 +618,7 @@ void WM_operator_type_modal_from_exec_for_object_edit_coords(struct wmOperatorTy
 void WM_uilisttype_init(void);
 struct uiListType *WM_uilisttype_find(const char *idname, bool quiet);
 bool WM_uilisttype_add(struct uiListType *ult);
-void WM_uilisttype_freelink(struct uiListType *ult);
+void WM_uilisttype_remove_ptr(struct Main *bmain, struct uiListType *ult);
 void WM_uilisttype_free(void);
 
 void WM_uilisttype_to_full_list_id(const struct uiListType *ult,
diff --git a/source/blender/windowmanager/intern/wm_init_exit.c b/source/blender/windowmanager/intern/wm_init_exit.c
index fa087f5e226..d7ea47fc625 100644
--- a/source/blender/windowmanager/intern/wm_init_exit.c
+++ b/source/blender/windowmanager/intern/wm_init_exit.c
@@ -553,7 +553,6 @@ void WM_exit_ex(bContext *C, const bool do_python)
   wm_surfaces_free();
   wm_dropbox_free();
   WM_menutype_free();
-  WM_uilisttype_free();
 
   /* all non-screen and non-space stuff editors did, like editmode */
   if (C) {
@@ -609,6 +608,8 @@ void WM_exit_ex(bContext *C, const bool do_python)
   wm_gizmomaptypes_free();
   wm_gizmogrouptype_free();
   wm_gizmotype_free();
+  /* Same for UI-list types. */
+  WM_uilisttype_free();
 
   BLF_exit();
 
diff --git a/source/blender/windowmanager/intern/wm_uilist_type.c b/source/blender/windowmanager/intern/wm_uilist_type.c
index 6d298ee63f1..468ea7e4d5b 100644
--- a/source/blender/windowmanager/intern/wm_uilist_type.c
+++ b/source/blender/windowmanager/intern/wm_uilist_type.c
@@ -23,8 +23,10 @@
 #include <stdio.h>
 #include <string.h>
 
+#include "BLI_listbase.h"
 #include "BLI_sys_types.h"
 
+#include "DNA_space_types.h"
 #include "DNA_windowmanager_types.h"
 
 #include "MEM_guardedalloc.h"
@@ -32,9 +34,11 @@
 #include "UI_interface.h"
 
 #include "BLI_ghash.h"
+#include "BLI_listbase.h"
 #include "BLI_string.h"
 #include "BLI_utildefines.h"
 
+#include "BKE_main.h"
 #include "BKE_screen.h"
 
 #include "WM_api.h"
@@ -64,8 +68,62 @@ bool WM_uilisttype_add(uiListType *ult)
   return 1;
 }
 
-void WM_uilisttype_freelink(uiListType *ult)
+static void wm_uilisttype_unlink_from_region(const uiListType *ult, ARegion *region)
 {
+  LISTBASE_FOREACH (uiList *, list, &region->ui_lists) {
+    if (list->type == ult) {
+      /* Don't delete the list, it's not just runtime data but stored in files. Freeing would make
+       * that data get lost. */
+      list->type = NULL;
+    }
+  }
+}
+
+static void wm_uilisttype_unlink_from_area(const uiListType *ult, ScrArea *area)
+{
+  LISTBASE_FOREACH (SpaceLink *, space_link, &area->spacedata) {
+    ListBase *regionbase = (space_link == area->spacedata.first) ? &area->regionbase :
+                                                                   &space_link->regionbase;
+    LISTBASE_FOREACH (ARegion *, region, regionbase) {
+      wm_uilisttype_unlink_from_region(ult, region);
+    }
+  }
+}
+
+/**
+ * For all lists representing \a ult, clear their `uiListType` pointer. Use when a list-type is
+ * deleted, so that the UI doesn't keep references to it.
+ *
+ * This is a common pattern for unregistering (usually .py defined) types at runtime, e.g. see
+ * #WM_gizmomaptype_group_unlink().
+ * Note that unlike in some other cases using this pattern, we don't actually free the lists with
+ * type \a ult, we just clear the reference to the type. That's because UI-Lists are written to
+ * files and we don't want them to get lost together with their (user visible) settings.
+ */
+static void wm_uilisttype_unlink(Main *bmain, const uiListType *ult)
+{
+  for (wmWindowManager *wm = bmain->wm.first; wm != NULL; wm = wm->id.next) {
+    LISTBASE_FOREACH (wmWindow *, win, &wm->windows) {
+      LISTBASE_FOREACH (ScrArea *, global_area, &win->global_areas.areabase) {
+        wm_uilisttype_unlink_from_area(ult, global_area);
+      }
+    }
+  }
+
+  for (bScreen *screen = bmain->screens.first; screen != NULL; screen = screen->id.next) {
+    LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+      wm_uilisttype_unlink_from_area(ult, area);
+    }
+
+    LISTBASE_FOREACH (ARegion *, region, &screen->regionbase) {
+      wm_uilisttype_unlink_from_region(ult, region);
+    }
+  }
+}
+
+void WM_uilisttype_remove_ptr(Main *bmain, uiListType *ult)
+{
+  wm_uilisttype_unlink(bmain, ult);
 
   bool ok = BLI_ghash_remove(uilisttypes_hash, ult->idname, NULL, MEM_freeN);