GDB -Wmissing-prototypes and flex troubles

Joel Brobecker
Wed Jun 13 04:38:00 GMT 2012

>   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 );

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...


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