Fix broken handling of constraints reordering with library overrides

Alternative to D13291 (description partially copied from there).

New drag & drop reordering code would call constraints reordering
operator with the generic context, and not the one from the panel's
layout. missing the "constraint" member which is mandatory for poll
function to properly deal with override vs. local constraints.

For this to work in a decent way, there needs to be some panel-wide
context that we can restore when executing callbacks outside of the
normal draw context. So similar to uiLayoutSetContextPointer() to set
context on a layout level, this introduces
UI_panel_context_pointer_set() for panel level context (this calls the
former for the current panel root layout as well).

Differential Revision: https://developer.blender.org/D13308

source/blender/editors/include/UI_interface.h

@@ -1766,6 +1766,8 @@ void UI_panel_header_buttons_begin(struct Panel *panel);
 void UI_panel_header_buttons_end(struct Panel *panel);
 void UI_panel_end(struct Panel *panel, int width, int height);
 
+void UI_panel_context_pointer_set(struct Panel *panel, const char *name, struct PointerRNA *ptr);
+
 bool UI_panel_is_closed(const struct Panel *panel);
 bool UI_panel_is_active(const struct Panel *panel);
 void UI_panel_label_offset(const struct uiBlock *block, int *r_x, int *r_y);

source/blender/editors/interface/interface_panel.c

@@ -486,8 +486,12 @@ static void reorder_instanced_panel_list(bContext *C, ARegion *region, Panel *dr
   /* Set the bit to tell the interface to instanced the list. */
   drag_panel->flag |= PNL_INSTANCED_LIST_ORDER_CHANGED;
 
+  CTX_store_set(C, drag_panel->runtime.context);
+
   /* Finally, move this panel's list item to the new index in its list. */
   drag_panel->type->reorder(C, drag_panel, move_to_index);
+
+  CTX_store_set(C, NULL);
 }
 
 /**
@@ -2458,6 +2462,17 @@ static void ui_panel_custom_data_set_recursive(Panel *panel, PointerRNA *custom_
   }
 }
 
+/**
+ * Set a context for this entire panel and its current layout. This should be used whenever panel
+ * callbacks that are called outside of regular drawing might require context. Currently it affects
+ * the #PanelType.reorder callback only.
+ */
+void UI_panel_context_pointer_set(Panel *panel, const char *name, PointerRNA *ptr)
+{
+  uiLayoutSetContextPointer(panel->layout, name, ptr);
+  panel->runtime.context = uiLayoutGetContextStore(panel->layout);
+}
+
 void UI_panel_custom_data_set(Panel *panel, PointerRNA *custom_data)
 {
   BLI_assert(panel->type != NULL);

source/blender/editors/interface/interface_templates.c

@@ -2727,7 +2727,12 @@ static void draw_constraint_header(uiLayout *layout, Object *ob, bConstraint *co
   PointerRNA ptr;
   RNA_pointer_create(&ob->id, &RNA_Constraint, con, &ptr);
 
-  uiLayoutSetContextPointer(layout, "constraint", &ptr);
+  if (block->panel) {
+    UI_panel_context_pointer_set(block->panel, "constraint", &ptr);
+  }
+  else {
+    uiLayoutSetContextPointer(layout, "constraint", &ptr);
+  }
 
   /* Constraint type icon. */
   uiLayout *sub = uiLayoutRow(layout, false);

source/blender/gpencil_modifiers/intern/MOD_gpencil_ui_common.c

@@ -232,7 +232,7 @@ PointerRNA *gpencil_modifier_panel_get_property_pointers(Panel *panel, PointerRN
   UI_block_lock_clear(block);
   UI_block_lock_set(block, ID_IS_LINKED((Object *)ptr->owner_id), ERROR_LIBDATA_MESSAGE);
 
-  uiLayoutSetContextPointer(panel->layout, "modifier", ptr);
+  UI_panel_context_pointer_set(panel, "modifier", ptr);
 
   return ptr;
 }
@@ -312,7 +312,7 @@ static void gpencil_modifier_panel_header(const bContext *UNUSED(C), Panel *pane
   PointerRNA *ptr = UI_panel_custom_data_get(panel);
   GpencilModifierData *md = (GpencilModifierData *)ptr->data;
 
-  uiLayoutSetContextPointer(panel->layout, "modifier", ptr);
+  UI_panel_context_pointer_set(panel, "modifier", ptr);
 
   const GpencilModifierTypeInfo *mti = BKE_gpencil_modifier_get_info(md->type);
   bool narrow_panel = (panel->sizex < UI_UNIT_X * 9 && panel->sizex != 0);

source/blender/gpencil_modifiers/intern/MOD_gpencildash.c

@@ -313,8 +313,6 @@ static void panel_draw(const bContext *C, Panel *panel)
                  UI_TEMPLATE_LIST_FLAG_NONE);
 
   uiLayout *col = uiLayoutColumn(row, false);
-  uiLayoutSetContextPointer(col, "modifier", ptr);
-
   uiLayout *sub = uiLayoutColumn(col, true);
   uiItemO(sub, "", ICON_ADD, "GPENCIL_OT_segment_add");
   uiItemO(sub, "", ICON_REMOVE, "GPENCIL_OT_segment_remove");

source/blender/makesdna/DNA_screen_types.h

@@ -154,6 +154,9 @@ typedef struct Panel_Runtime {
   /* Pointer to the panel's block. Useful when changes to panel #uiBlocks
    * need some context from traversal of the panel "tree". */
   struct uiBlock *block;
+
+  /* Non-owning pointer. The context is stored in the block. */
+  struct bContextStore *context;
 } Panel_Runtime;
 
 /** The part from uiBlock that needs saved in file. */

source/blender/modifiers/intern/MOD_ui_common.c

@@ -132,7 +132,7 @@ PointerRNA *modifier_panel_get_property_pointers(Panel *panel, PointerRNA *r_ob_
   uiBlock *block = uiLayoutGetBlock(panel->layout);
   UI_block_lock_set(block, ID_IS_LINKED((Object *)ptr->owner_id), ERROR_LIBDATA_MESSAGE);
 
-  uiLayoutSetContextPointer(panel->layout, "modifier", ptr);
+  UI_panel_context_pointer_set(panel, "modifier", ptr);
 
   return ptr;
 }
@@ -304,7 +304,7 @@ static void modifier_panel_header(const bContext *C, Panel *panel)
   ModifierData *md = (ModifierData *)ptr->data;
   Object *ob = (Object *)ptr->owner_id;
 
-  uiLayoutSetContextPointer(panel->layout, "modifier", ptr);
+  UI_panel_context_pointer_set(panel, "modifier", ptr);
 
   const ModifierTypeInfo *mti = BKE_modifier_get_info(md->type);
   Scene *scene = CTX_data_scene(C);

source/blender/shader_fx/intern/FX_ui_common.c

@@ -117,7 +117,7 @@ PointerRNA *shaderfx_panel_get_property_pointers(Panel *panel, PointerRNA *r_ob_
     RNA_pointer_create(ptr->owner_id, &RNA_Object, ptr->owner_id, r_ob_ptr);
   }
 
-  uiLayoutSetContextPointer(panel->layout, "shaderfx", ptr);
+  UI_panel_context_pointer_set(panel, "shaderfx", ptr);
 
   return ptr;
 }