On Thu, Jul 04, 2019 at 01:27:27PM +0200, Florian Weimer wrote: > Implicit function declarations were removed from C99, more than twenty > years ago. So far, GCC only warns about them because there were too > many old configure scripts where an error would lead to incorrect > configure check failures. > > I can try to fix the remaining configure scripts in Fedora and submit > the required changes during this summer and fall. > > I would appreciate if GCC 10 refused to declare functions implicitly by > default.
[ The warning for it is enabled by default with -std=c99 or later, and with -Wall as well. And people still ignore that? Wow. ] We already have an option for that (-Werror=implicit-function-declaration), and it is an error by default with -pedantic-errors already. If you are asking to make it an error by default, I second that; there needs to be a wat to turn it off though. Maybe it should be an error for c99 and later only, anyway? > According to my observations, lack of an error diagnostic has turned > into a major usability issue. For bugs related to pointer truncation, > we could perhaps change the C front end to produce a hard error if an > int value returned from an implicitly declared function is converted to > a pointer. No, if we allow implicit declarations at all, your proposal would error on valid (but improbable :-) ) code. We should only ever give hard errors if we *know* something is wrong. > Implicit int we should remove as well. Checking configure scripts for > both issues at the same time would not be much more work. We could enable -Wimplicit-int by default for c99 and later, maybe even its -Werror- version. This conflicts with at least -fms-extensions it, seems, dunno what to do there. Segher
