Should a disabled warning be allowed to be promoted to an error(Bugzilla PR 70275)?

[Manuel López-Ibáñez]

> On 03/28/2016 01:56 PM, Florian Weimer wrote:
>>> In Bugzilla PR # 70275, Manuel López-Ibáñez reports that even though
>>> he provides the "-Werror=return-type" option, the compiler doesn't
>>> flag the warning/error about a control reaching the end of a non-void
>>> function, due to the presence of the "-w" option.  He points out that
>>> clang++ wtill flags the promoted warning even though warnings are
>>> inhibited.

I did not report the bug and did not mention anything of the above. I only 
commented on why GCC works like it works and how one can change the behaviour 
if so desired. I don't care one way or the other and I can see benefits for 
either behaviour.

>> I think -w is ordered with respect to the other warning obtions, and
>> -w inhibits previously requested warnings, and future -W flags may
>> enable other warnings.  With this in mind, I agree that the current
>> GCC behavior is consistent and probably not a bug.

The command-line order does not affect '-w' and there is no way to undo '-w'. 
It is a global boolean switch independent of anything else (including pragmas) 
that disables warnings just before they are re-classified (by pragmas or 
-Werror=) into something else. This means that if -Wfoobar is given in the 
command-line (or enabled by a pragma) and it requires an expensive analysis, 
this analysis is done even in the presence of -w, only the warning message is 
not emitted.

One question to answer if the behaviour does change is what would be the effect 
of using '-w' on warning options enabled by #pragmas. Some people may still 
want a switch that simply disables all warnings no matter how they are enabled.

Cheers,

	Manuel.