[Bug c/96284] Outdated C features should be made errors with newer standards

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96284

Eric Gallager <egallager at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |egallager at gcc dot gnu.org,
                   |                            |fw at gcc dot gnu.org

--- Comment #5 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to David Brown from comment #0)
> While C has tried to remain backwards compatible with each new standards
> revision, some changes have been made so that particularly unsafe features
> from old code are no longer supported.  gcc has (reasonably enough) tried to
> keep support for old features, but when something has been deprecated for
> decades, perhaps it is time for it to be treated as an error by default and
> require an explicit flag.  (This is in the same style as bug 85678 making
> "-fno-common" the default.)
> 
> For example, implicit function declarations from K&R C were made obsolescent
> in C90, and removed from the language in C99.  But by default, they still
> only cause a warning (-Wimplicit-function-declaration) in gcc, no matter
> what standard is picked.
> 
> Could this be made an error by default
> (-Werror=implicit-function-declarations) ?  Let those who want to compile
> old code with implicit function declarations, do so with an explicit flag.

I think Florian Weimer tried this and it broke the majority of configure
scripts in existence...