Fix [#22199] Cloth Cache Panel > Disk Cache doesn't work

Condition for this to work (.blend file must be saved) was poorly communicated 
in the UI (printfs are no good for this - ideally should use reports). Tweaked this a bit.

release/scripts/ui/properties_physics_common.py

@@ -20,6 +20,7 @@
 
 narrowui = 180
 
+import bpy
 
 def point_cache_ui(self, context, cache, enabled, particles, smoke):
     layout = self.layout
@@ -67,7 +68,10 @@ def point_cache_ui(self, context, cache, enabled, particles, smoke):
             sub = col.column()
             sub.enabled = enabled
             sub.prop(cache, "quick_cache")
-            col.prop(cache, "disk_cache")
+            
+            sub = col.column()
+            sub.enabled = bpy.data.file_is_saved
+            sub.prop(cache, "disk_cache")
             col.label(text=cache.info)
 
         

source/blender/blenkernel/intern/pointcache.c

@@ -2652,6 +2652,7 @@ void BKE_ptcache_mem_to_disk(PTCacheID *pid)
 			ptcache_file_init_pointers(pf);
 
 			if(!ptcache_file_write_header_begin(pf) || !pid->write_header(pf)) {
+				if (G.f & G_DEBUG) 
 					printf("Error writing to disk cache\n");
 				cache->flag &= ~PTCACHE_DISK_CACHE;
 
@@ -2662,6 +2663,7 @@ void BKE_ptcache_mem_to_disk(PTCacheID *pid)
 			for(i=0; i<pm->totpoint; i++) {
 				ptcache_copy_data(pm->cur, pf->cur);
 				if(!ptcache_file_write_data(pf)) {
+					if (G.f & G_DEBUG) 
 						printf("Error writing to disk cache\n");
 					cache->flag &= ~PTCACHE_DISK_CACHE;
 
@@ -2678,6 +2680,7 @@ void BKE_ptcache_mem_to_disk(PTCacheID *pid)
 				BKE_ptcache_write_cache(pid, 0);
 		}
 		else
+			if (G.f & G_DEBUG) 
 				printf("Error creating disk cache file\n");
 	}
 }
@@ -2688,6 +2691,7 @@ void BKE_ptcache_toggle_disk_cache(PTCacheID *pid)
 
 	if (!G.relbase_valid){
 		cache->flag &= ~PTCACHE_DISK_CACHE;
+		if (G.f & G_DEBUG) 
 			printf("File must be saved before using disk cache!\n");
 		return;
 	}

source/blender/makesrna/intern/rna_main.c

@@ -50,6 +50,10 @@ static void rna_Main_debug_set(PointerRNA *ptr, const int value)
 		G.f &= ~G_DEBUG;
 }
 
+static int rna_Main_fileissaved_get(PointerRNA *ptr)
+{
+	return G.relbase_valid;
+}
 
 static void rna_Main_filename_get(PointerRNA *ptr, char *value)
 {
@@ -309,6 +313,11 @@ void RNA_def_main(BlenderRNA *brna)
 	RNA_def_property_clear_flag(prop, PROP_EDITABLE);
 	RNA_def_property_ui_text(prop, "Filename", "Path to the .blend file");
 	
+	prop= RNA_def_property(srna, "file_is_saved", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+	RNA_def_property_boolean_funcs(prop, "rna_Main_fileissaved_get", NULL);
+	RNA_def_property_ui_text(prop, "File is Saved", "Has the current session been saved to disk as a .blend file");
+
 	prop= RNA_def_property(srna, "debug", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_funcs(prop, "rna_Main_debug_get", "rna_Main_debug_set");
 	RNA_def_property_ui_text(prop, "Debug", "Print debugging information in console");

source/blender/makesrna/intern/rna_object_force.c

@@ -709,7 +709,7 @@ static void rna_def_pointcache(BlenderRNA *brna)
 
 	prop= RNA_def_property(srna, "disk_cache", PROP_BOOLEAN, PROP_NONE);
 	RNA_def_property_boolean_sdna(prop, NULL, "flag", PTCACHE_DISK_CACHE);
-	RNA_def_property_ui_text(prop, "Disk Cache", "Save cache files to disk");
+	RNA_def_property_ui_text(prop, "Disk Cache", "Save cache files to disk (.blend file must be saved first)");
 	RNA_def_property_update(prop, NC_OBJECT, "rna_Cache_toggle_disk_cache");
 
 	prop= RNA_def_property(srna, "outdated", PROP_BOOLEAN, PROP_NONE);