Preferences: add is_dirty member

Tag preferences as dirty when changed (prepare for adding auto-save).

source/blender/blenkernel/intern/blendfile.c

@@ -617,6 +617,9 @@ bool BKE_blendfile_userdef_write_all(ReportList *reports)
     }
   }
 
+  if (ok) {
+    U.runtime.is_dirty = false;
+  }
   return ok;
 }
 

source/blender/editors/interface/interface_handlers.c

@@ -7566,6 +7566,11 @@ static void button_activate_exit(
     if (block->flag & UI_BLOCK_POPUP_MEMORY) {
       ui_popup_menu_memory_set(block, but);
     }
+
+    /* Not very elegant, but ensures preference changes force re-save. */
+    if (but->rnaprop && (but->rnapoin.data == &U)) {
+      U.runtime.is_dirty = true;
+    }
   }
 
   /* disable tooltips until mousemove + last active flag */

source/blender/makesdna/DNA_userdef_types.h

@@ -537,6 +537,11 @@ typedef struct WalkNavigation {
   char _pad0[6];
 } WalkNavigation;
 
+typedef struct UserDef_Runtime {
+  char is_dirty;
+  char _pad0[7];
+} UserDef_Runtime;
+
 typedef struct UserDef {
   /* UserDef has separate do-version handling, and can be read from other files */
   int versionfile, subversionfile;
@@ -767,6 +772,9 @@ typedef struct UserDef {
   char viewport_aa;
 
   char _pad5[2];
+
+  /** Runtime data (keep last). */
+  UserDef_Runtime runtime;
 } UserDef;
 
 /* from blenkernel blender.c */

source/blender/makesrna/intern/rna_userdef.c

@@ -184,8 +184,11 @@ static void rna_userdef_version_get(PointerRNA *ptr, int *value)
   value[2] = userdef->subversionfile;
 }
 
-static void rna_userdef_update(Main *UNUSED(bmain), Scene *UNUSED(scene), PointerRNA *UNUSED(ptr))
+static void rna_userdef_update(Main *UNUSED(bmain), Scene *UNUSED(scene), PointerRNA *ptr)
 {
+  UserDef *userdef = (UserDef *)ptr->data;
+  userdef->runtime.is_dirty = true;
+
   WM_main_add_notifier(NC_WINDOW, NULL);
 }