[Spice-devel] [PATCH spice-gtk v5 6/6] usb-device-widget: Migrate to GtkGrid from GtkBox

[Daniel P. Berrange]

On Mon, Feb 20, 2017 at 12:44:52PM +0100, Victor Toso wrote:
> Hi,
> 
> On Fri, Feb 17, 2017 at 11:24:55AM +0100, Pavel Grunt wrote:
> > GtkVBox is deprecated since Gtk 3.2, GtkBox is going to be
> > deprecated. Just use the GtkGrid and GtkContainer api.
> 
> Sure
> 
> > ---
> > GtkContainer is an abstract class, so let's use the Grid with the
> > vertical orientation
> 
> At first I thought this was a ABI break but it was questioned in the
> public IRC and the SpiceUsbDeviceWidget should not be subclassed, so
> this should be fine. The chat is below for reference.

Saying on IRC that it shouldn't be subclassed doesn't mean that it hasn't
been sub-classed, particularly if this rule about not-subclassing has not
been documented anywhere for app developers to learn about it...

> pgrunt | i have this patch https://paste.fedoraproject.org/.. is it abi
>          break ? SpiceUsbDeviceWidget is publically a GtkWidget
>          https://www.spice-space.org/api/spice-gtk/spice-gtk-SpiceUsbDeviceWidget.html,
>          but internally I am changing it from GtkBox to GtkContainer, so
>          binary is different api is same
> teuf   | yeah, depends if we consider it a valid/likely use case to
>          derive from SpiceUsbDeviceWidget or not
> teuf   | (ie whether G_DECLARE_FINAL_TYPE could be used in the header or
>          not)
> pgrunt | hm, it should be final
> teuf   | note that it's glib 2.44+ only
> pgrunt | well i can keep the type GtkBox and use the gtk_container api
>          anyway

Even if you keep the type GtkBox in the struct, but change the
G_DEFINE_TYPE to use GTK_CONTAINER, instad of GTK_TYPE_BOX, that is
still technically an API break as you've changed the semantics of
the widget. ie if a subclass exists, and they are calling any of
the gtk_box_* APIs those will break, even though the struct still
contains the GtkBox content. ie while ABI refers to compiled type
sizes, API covers semantics of the types too, and you need to
preserve both ABI + API if you are not changing the soname.

Regards,
Daniel
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