Libguestfs - Sep 2022 - [p2v PATCH 1/7] "shutdown_actions": suppress "missing initializer" warnings/errors

gcc reports:
> gui.c:1795:3: error: missing initializer for field ?padding? of
> ?GActionEntry? {aka ?const struct _GActionEntry?}
> [-Werror=missing-field-initializers]
>  1795 |   { "shutdown", activate_action, NULL, NULL, NULL },
>
> gui.c:1796:3: error: missing initializer for field ?padding? of
> ?GActionEntry? {aka ?const struct _GActionEntry?}
> [-Werror=missing-field-initializers]
>  1796 |   { "reboot", activate_action, NULL, NULL, NULL },
I've found this only now because:

- this is the first time I'm building virt-p2v with GTK3,

- the "shutdown_actions" array depends on USE_POPOVERS which depends
on
  GTK3 being selected,

- the "missing-field-initializers" warning (treated as an error) has
  recently been enabled via "-Wextra" in commit 391f9833d398
("p2v-c.m4:
  elicit a stricter set of warnings from gcc", 2022-09-23).

The C-language documentation for GActionEntry is silent on the
"padding"
array:

  https://docs.gtk.org/gio/struct.ActionEntry.html

However, the D-language docs expose it:

  https://api.gtkd.org/gio.c.types.GActionEntry.html

Provide the missing field initializer.

Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 gui.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gui.c b/gui.c
index 49301d9a985b..4faaa710ed90 100644
--- a/gui.c
+++ b/gui.c
@@ -1792,8 +1792,8 @@ static gboolean close_running_dialog (GtkWidget *w,
GdkEvent *event, gpointer da
 
 #ifdef USE_POPOVERS
 static const GActionEntry shutdown_actions[] = {
-  { "shutdown", activate_action, NULL, NULL, NULL },
-  { "reboot", activate_action, NULL, NULL, NULL },
+  { "shutdown", activate_action, NULL, NULL, NULL, { 0 } },
+  { "reboot", activate_action, NULL, NULL, NULL, { 0 } },
 };
 #endif

On Mon, Sep 26, 2022 at 10:18:06AM +0200, Laszlo Ersek
wrote:
> gcc reports:
> 
> > gui.c:1795:3: error: missing initializer for field ?padding? of
> > ?GActionEntry? {aka ?const struct _GActionEntry?}
> > [-Werror=missing-field-initializers]
> >  1795 |   { "shutdown", activate_action, NULL, NULL, NULL },
> >
> > gui.c:1796:3: error: missing initializer for field ?padding? of
> > ?GActionEntry? {aka ?const struct _GActionEntry?}
> > [-Werror=missing-field-initializers]
> >  1796 |   { "reboot", activate_action, NULL, NULL, NULL },
> 
> I've found this only now because:
> 
> - this is the first time I'm building virt-p2v with GTK3,
> 
> - the "shutdown_actions" array depends on USE_POPOVERS which
depends on
>   GTK3 being selected,
> 
> - the "missing-field-initializers" warning (treated as an error)
has
>   recently been enabled via "-Wextra" in commit 391f9833d398
("p2v-c.m4:
>   elicit a stricter set of warnings from gcc", 2022-09-23).
> 
> The C-language documentation for GActionEntry is silent on the
"padding"
> array:
> 
>   https://docs.gtk.org/gio/struct.ActionEntry.html
> 
> However, the D-language docs expose it:
> 
>   https://api.gtkd.org/gio.c.types.GActionEntry.html
> 
> Provide the missing field initializer.
> 
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
>  gui.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gui.c b/gui.c
> index 49301d9a985b..4faaa710ed90 100644
> --- a/gui.c
> +++ b/gui.c
> @@ -1792,8 +1792,8 @@ static gboolean close_running_dialog (GtkWidget *w,
GdkEvent *event, gpointer da
>  
>  #ifdef USE_POPOVERS
>  static const GActionEntry shutdown_actions[] = {
> -  { "shutdown", activate_action, NULL, NULL, NULL },
> -  { "reboot", activate_action, NULL, NULL, NULL },
> +  { "shutdown", activate_action, NULL, NULL, NULL, { 0 } },
> +  { "reboot", activate_action, NULL, NULL, NULL, { 0 } },
>  };
Notice the header decl says 'padding' is private hence why it is
not documented.

struct _GActionEntry
{
  const gchar *name;

  void (* activate) (GSimpleAction *action,
                     GVariant      *parameter,
                     gpointer       user_data);

  const gchar *parameter_type;

  const gchar *state;

  void (* change_state) (GSimpleAction *action,
                         GVariant      *value,
                         gpointer       user_data);

  /*< private >*/
  gsize padding[3];
};


The purpose of this 'padding' entry is to reserve space in the struct
for future usage. Apps should never touch the padding field, since it
can change in future. ie that 3 element array can turn into three
separate public fields later, and then the compound initializer above
would be invalid.

The right way to declare this is using named initializers:

  { .name = "shutdown", .activate = activate_action },
  { .name = "reboot", .activate = activate_action },


With regards,
Daniel
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