[Geany-devel] [PATCH 2/3] Prevent -Wmissing-prototypes report warning when compiling a plugin

[Jiří Techet]

On Thu, Jun 10, 2010 at 13:49, Nick Treleaven
<nick.treleaven at btinternet.com> wrote:
> On Thu, 10 Jun 2010 13:33:44 +0200
> Jiří Techet <techet at gmail.com> wrote:
>
>> On Thu, Jun 10, 2010 at 13:05, Nick Treleaven
>> <nick.treleaven at btinternet.com> wrote:
>> > On Wed,  9 Jun 2010 21:40:58 +0200
>> > Jiří Techet <techet at gmail.com> wrote:
>> >
>> >> Signed-off-by: Jiří Techet <techet at gmail.com>
>> >> ---
>> >>  src/plugindata.h |    2 ++
>> >
>> >> +     gint plugin_version_check(gint abi_ver);\
>> >>       gint plugin_version_check(gint abi_ver) \
>> >>       { \
>> >
>> > Why is this necessary?
>> >
>>
>> If you don't compile the plugins with -Wmissing-prototypes then you
>> don't get any warnings if you use a function that hasn't been
>> declared (imagine you make a typo in a call of an API function or any
>> of your internal functions). The plugin compiles just fine, but then
>> it doesn't get loaded by geany on runtime and you have to start
>> searching for what symbol is missing (using LD_DEBUG).
>
> Wouldn't you get a warning with -Wall:
>
> int main(int argc, char **argv)
> {
>        foo();
>        return 0;
> }
>
> $ gcc -c untitled.c -Wall
> untitled.c: In function ‘main’:
> untitled.c:28: warning: implicit declaration of function ‘foo’
>

Ah, sorry, you're right, this isn't the case - it's a different one.
Imagine you have:

foo.h:
void foo(void);

foo.c:
#include "foo.h"

void foo(void)
{
  printf("foo");
}

main.c:
#include "foo.h"

int main(int argc, char **argv)
{
  foo();
  return 0;
}

This is OK. Now you rename foo(void) in foo.c to foobar(void) but
forget to update the header. It compiles just fine because main.c
finds the declaration of foo(void) in foo.h, but its implementation is
missing (so the compiler thinks it's an extern symbol, but it's not
actually defined anywhere).

Just a note if you wish to use it - the declarations with no arguments
have to be declared as

void foo(void);

and not

void foo();

>>
>> -Wmissing-prototypes requires that for every non-static function there
>> is a previous declaration before it is defined/used. This is normally
>> satisfied because these are in the header files - this macro is just
>> an exceptional case.
>>
>> In general, I would recommend that geany uses a slightly more strict
>> set of warning options. I find the options used by gnome-common as a
>> reasonable set:
>>
>> -Wall -Wmissing-prototypes -Wnested-externs -Wpointer-arith -Wno-sign-compare
>>
>> You might consider using them for the whole geany.
>
> This is (probably) less strict than our recommended warnings, see the
> HACKING file (-W and -ansi):

I would have to check what exactly -W and -ansi consist of but I think
they don't contain -Wmissing-prototypes.

Jiri