Re: Changes in C++ FE regarding pedwarns to be errors are harmful

[Joe Buck <Joe dot Buck at synopsys dot COM>]

On Tue, Jan 08, 2008 at 11:28:22PM +0200, Ismail Dönmez wrote:
> Hi all,
> 
> Looks like gcc 4.3 has some rather inconvenient changes in C++ FE, with the 
> latest trunk. Lets see with an example :
> 
> [~]> cat test.cpp
> #define foo bar
> #define foo baz
> 
> [~]> g++ -c test.cpp
> test.cpp:2:1: error: "foo" redefined
> test.cpp:1:1: error: this is the location of the previous definition
> 
> I don't know the reasoning behind this change but this breaks many C++ 
> programs unless -fpermissive is used. Why? Because everybody loves to install 
> their own config.h (Python, libmp4v2 being nice examples) which just 
> carelessly #define anything its asked for with ifndef ... endif .
> 
> Now flash back to real world: this breaks any C++ application that uses 
> Python, libmp4v2, libjpeg and possibly many others. And I think this is a 
> real bad behaviour change and I am not sure if its worth all the trouble.

There's certainly an argument that this change is ill-advised.  However,
your statements in the last paragraph aren't true: most quality open
source projects have a "no warnings" rule (or at least try to eliminate
warnings), and most programmers know about #undef.  Since people have
already built whole distros with the gcc from the trunk, clearly they
are managing to build C++ applications that use Python, libmp4v2, libjpeg
etc.