GDB -Wmissing-prototypes and flex troubles

Mark Kettenis
Wed Jun 13 05:58:00 GMT 2012

> Date: Tue, 12 Jun 2012 21:37:48 -0700
> From: Joel Brobecker <>
> >   Should we:
> > 1) Specify a minimal version for flex?
> > 2) disable missing-prototypes option 
> > for ada-exp.c compilation?
> > 3) Do 2) if version if below 
> > minimum version adding those prototypes?
> The lazy way would be to require a minimal version for flex.
> I would be OK with that, although it is true that it is a bit of
> a shame that the user does not get an error at configure time.
> It should be relatively easy to do, except that this would force
> me to upgrade many installs of flex on some of AdaCore's machines.
> I don't mind doing the update too much, and I should, except
> I usually find out at the wrong moment, and I then just get past
> the error by copy/pasting the compile command, removing the -Werror
> flag, and then resume the build. And also, an error would be
> preventing people from building a release with an older version
> of flex, even though the warnings would be harmless and non-fatal.
> I don't think we want to unilaterally disable -Werror for ada-lex.c.
> We'd open the door to allowing warnings back in again, when we did
> all the work to clean them up.
> A variation of 3. Something like the following close to the start
> of ada-lex.l:
>     #if <FLEX_VERSION> < <2.5.35>
>     /* Older versions of flex do not provide prototypes for these functions.
>        Provide them ourselves, to avoid -Wmissing-prototypes warnings.  */
>     int yylex_destroy (void );
>     int yyget_debug (void );
>     void yyset_debug (int debug_flag  );
>     YY_EXTRA_TYPE yyget_extra (void );
>     [...]
>     #endif
> I am not completly sure that this is going to work, maybe if some
> types are missing, for instance. Or maybe the prototypes depend on
> the version of flex.
> With all this being said, your option (3) is attractive. Except
> that in terms of implementation, it forces us to have a special
> rules for ada-lex.o.
> All in all, I tend to vote for the status quo...

Same here.  The version of flex in the OpenBSD base system reports
itself as 2.5.4, yet I don't see the problem that Pierre reports.  So
it seems that the problem was introduced in a later version and then
fixed again.  Given that there is a workaround, and releases don't
suffer from the problem because we disable -Werror there, I'd say we
leave things as they are.

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