MacPorts and clang

[Ryan Schmidt]

On Mar 3, 2011, at 10:19, Jack Howarth wrote:

> On Thu, Mar 03, 2011 at 09:48:40AM -0600, Ryan Schmidt wrote:
>> 
> 
>> On Mar 3, 2011, at 09:40, Jack Howarth wrote:
>> 
>>> Are there any plans to attempt to move MacPorts towards
>>> building with clang once Xcode 4 is released? Considering that
>>> we have so many packages supporting gcc4x variants to build with
>>> FSF gcc, it seems strange not to do the same for clang.
>>>            Jack
>>> ps I assume that Xcode 4 won't be held up until Lion is released so
>>> these clang variants could be first done on Snow Leopard. It is unclear
>>> from http://developer.apple.com/technologies/tools/whats-new.html
>>> if the clang c++ support in Xcode 4.0 will use the existing libstdc++
>>> or the new libc++ instead. It would be nice if it were the latter.
>> 
>> Ports build with the standard Xcode gcc compilers unless there is a good reason not to. The reason why many ports have variants to use MacPorts gcc compilers is not because they particularly want to use the MacPorts gcc C or C++ compilers, but because they want to use a Fortran compiler, which Xcode doesn't provide.
> 
>   That wasn't my experience. When I contributed the pymol packaging, some of the other MacPorts
> developers insisted on gcc4x variants despite the fact that pymol doesn't contain any fortran code.
> A clang variant still might be a nice idea to provide a test bed for finding out which packages have
> build issues and for filing reports or sending patches upstream. It is unclear from the published
> information on Lion what Apple's intentions are for clang/libc++ but I am hoping they might be 
> aggressive and, while building Lion with gcc-4.2, configure the standard system compilers to clang.
> I believe we saw this done earlier in Mac OS X development (perhaps the gcc-3.3 to gcc-4.0
> transition) where the Xcode defaulted to a newer gcc than was actually used to build the matching
> OS release.

The other reason some ports have gcc variants is because there is a desire to compile all related programs and libraries using the same compiler, to avoid hard-to-diagnose problems. So if a port uses a gcc variant in order to use a fortran compiler, it's possible everything depending on that port for its libraries will also need to use the same gcc compiler, regardless whether it itself uses fortran.