Backport from https://gitlab.gnome.org/GNOME/dia/-/commit/f57ea2685034ddbafc19f35d9b525a12283d7c24

--- dia-0.97.3/lib/prop_geomtypes.c				2014-08-24 17:46:01.000000000 +0200
+++ dia-0.97.3/lib/prop_geomtypes.c.get_data_size		2024-03-02 22:11:06.700789662 +0100
@@ -129,9 +129,10 @@
 }
 
 static int 
-realprop_get_data_size(RealProperty *prop)
+realprop_get_data_size(void)
 {
-  return sizeof (prop->real_data);
+  RealProperty prop;
+  return sizeof (prop.real_data);
 }
 
 static const PropertyOps realprop_ops = {
@@ -242,9 +243,10 @@
 }
 
 static int 
-lengthprop_get_data_size(LengthProperty *prop)
+lengthprop_get_data_size(void)
 {
-  return sizeof (prop->length_data);
+  LengthProperty prop;
+  return sizeof (prop.length_data);
 }
 
 static const PropertyOps lengthprop_ops = {
@@ -358,9 +360,10 @@
 }
 
 static int 
-fontsizeprop_get_data_size(FontsizeProperty *prop)
+fontsizeprop_get_data_size(void)
 {
-  return sizeof (prop->fontsize_data);
+  FontsizeProperty prop;
+  return sizeof (prop.fontsize_data);
 }
 
 static const PropertyOps fontsizeprop_ops = {
--- dia-0.97.3/lib/prop_inttypes.c				2014-08-24 17:46:01.000000000 +0200
+++ dia-0.97.3/lib/prop_inttypes.c.get_data_size		2024-03-02 22:12:01.683149664 +0100
@@ -122,9 +122,10 @@
 }
 
 static int 
-charprop_get_data_size(CharProperty *prop)
+charprop_get_data_size(void)
 {
-  return sizeof (prop->char_data);
+  CharProperty prop;
+  return sizeof (prop.char_data);
 }
 
 
@@ -229,9 +230,10 @@
 }
 
 static int 
-boolprop_get_data_size(BoolProperty *prop)
+boolprop_get_data_size(void)
 {
-  return sizeof (prop->bool_data);
+  BoolProperty prop;
+  return sizeof (prop.bool_data);
 }
 
 
@@ -339,9 +341,10 @@
 }
 
 static int 
-intprop_get_data_size(IntProperty *prop)
+intprop_get_data_size(void)
 {
-  return sizeof (prop->int_data);
+  IntProperty prop;
+  return sizeof (prop.int_data);
 }
 
 static const PropertyOps intprop_ops = {
--- dia-0.97.3/lib/prop_text.c					2014-08-24 17:46:01.000000000 +0200
+++ dia-0.97.3/lib/prop_text.c.get_data_size			2024-03-02 22:12:46.741444615 +0100
@@ -208,9 +208,10 @@
 }
 
 static int 
-stringprop_get_data_size(StringProperty *prop)
+stringprop_get_data_size(void)
 {
-  return sizeof (prop->string_data); /* only the pointer */
+  StringProperty prop;
+  return sizeof (prop.string_data); /* only the pointer */
 }
 
 static StringListProperty *
--- dia-0.97.3/lib/properties.h					2014-08-24 17:46:01.000000000 +0200
+++ dia-0.97.3/lib/properties.h.get_data_size			2024-03-02 22:13:08.051584089 +0100
@@ -116,7 +116,7 @@
                                          void *base, guint offset, guint offset2);
 typedef void (*PropertyType_SetFromOffset)(Property *prop,
                                          void *base, guint offset, guint offset2);
-typedef int (*PropertyType_GetDataSize)(Property *prop);
+typedef int (*PropertyType_GetDataSize)(void);
 
 
 struct _PropertyOps {
--- dia-0.97.3/objects/custom/custom_object.c			2014-08-24 17:46:01.000000000 +0200
+++ dia-0.97.3/objects/custom/custom_object.c.get_data_size	2024-03-02 22:13:29.153722188 +0100
@@ -372,14 +372,7 @@
       info->prop_offsets[i].name = info->props[i].name;
       info->prop_offsets[i].type = info->props[i].type;
       info->prop_offsets[i].offset = offs;
-      /* FIXME:
-	 custom_object.c:328: warning: passing arg 1 of pointer to function 
-	 from incompatible pointer type
-	 We don't have a Property* here so there is not much we can do about.
-	 Maybe it even works cause the sizeof() in *_get_data_size can be
-	 calculated at compile time. Anyway, a mess ;) --hb
-      */
-      size = info->props[i].ops->get_data_size (&info->props[i]);
+      size = info->props[i].ops->get_data_size ();
       info->ext_attr_size += size;
       offs += size;
     }