RE: [PATCH-for-5.2? 1/2] tests/qtest: variable defined by g_autofree need to be initialized

[Chenqun (kuhn)]

> -----Original Message-----
> From: Peter Maydell [mailto:peter.maydell@linaro.org]
> Sent: Thursday, November 19, 2020 4:39 PM
> To: Chenqun (kuhn) <kuhn.chenqun@huawei.com>
> Cc: QEMU Developers <qemu-devel@nongnu.org>; QEMU Trivial
> <qemu-trivial@nongnu.org>; Hao Wu <wuhaotsh@google.com>; Havard
> Skinnemoen <hskinnemoen@google.com>; Zhanghailiang
> <zhang.zhanghailiang@huawei.com>; Thomas Huth <thuth@redhat.com>;
> Laurent Vivier <lvivier@redhat.com>; Euler Robot <euler.robot@huawei.com>
> Subject: Re: [PATCH-for-5.2? 1/2] tests/qtest: variable defined by g_autofree
> need to be initialized
> 
> On Thu, 19 Nov 2020 at 08:35, Chenqun (kuhn) <kuhn.chenqun@huawei.com>
> wrote:
> >
> > > -----Original Message-----
> > > >  static void tim_add_test(const char *name, const TestData *td,
> > > > GTestDataFunc fn)  {
> > > > -    g_autofree char *full_name;
> > > > -
> > > > -    full_name =
> g_strdup_printf("npcm7xx_timer/tim[%d]/timer[%d]/%s",
> > > > -                                tim_index(td->tim),
> > > timer_index(td->timer),
> > > > -                                name);
> > > > +    g_autofree char *full_name = g_strdup_printf(
> > > > +        "npcm7xx_timer/tim[%d]/timer[%d]/%s", tim_index(td->tim),
> > > > +        timer_index(td->timer), name);
> > >
> > > Which compiler is so unintelligent that it cannot see that a
> > > declaration immediately followed by an assignment must always initialize
> the variable ???
> > >
> > Hi Peter,
> >   Glib requires that all g_auto* macros must be initialized.
> >
> > https://developer.gnome.org/glib/stable/glib-Miscellaneous-Macros.html
> > #g-autofree
> 
> Yes, and we initialize it with the "full_name = ..." line.
> The g_autofree documentation says "this macro has similar constraints as
> g_autoptr()", and the g_autoptr() documentation says "You must initialise the
> variable in some way — either by use of an initialiser or by ensuring that it 
> is
> assigned to unconditionally before it goes out of scope."
> 
> In this case the test code is doing the second of those two things.

Emm, maybe I didn't get it right. I've tried something as following:
There are three pieces of code complied in GCC9.3 and GCC7.3.
Code1：
   g_autofree char *full_name;
   full_name = g_strdup_printf("npcm7xx_timer");

Code2:
   g_autofree char *full_name = g_strdup_printf("npcm7xx_timer");

Code3：
   g_autofree char *full_name;
   full_name = NULL;

The result is as follows:
  Code1: An warnig is generated for GCC7.3 or GCC9.3.

  Code2 and Code3: no any warnig whether compiler is GCC7.3 or GCC9.3.

I cannot explain why the Code1 warning is generated. But it always generates 
warning on the GCC compiler.

Thanks,
Chen Qun