Checking breakage of backward compatibility

[Richard Frith-Macdonald]

On 4 Oct 2006, at 12:46, David Ayers wrote:

> I'm almost indifferent on the subject.  But in practice I believe  
> people
> will unknowingly break binary compatibility and forget to bump the SO
> name.  I think this is worse than forcing folks to recompile apps just
> because the SO name bumped even though it didn't break binary
> compatibility.... but like I said.  I wouldn't mind either way.

That worries me too ... but I think we *must* try to be strict about it.
Is there any way we could devise an automated test for binary  
compatibility breakage?

It seems to me that it should be possible to catalogue and check  
externally available symbols (classes, functions, variables and  
constants) using standard tools to examine the binary.  It should  
also be possible to write a small program to inspect the objc runtime  
to determine ivar layout and method signature changes.

Doing this would also be a useful exercise for finding out what  
things are currently publicly exposed and should not be.

Tests could be run nightly on the current SVN trunk, providing  
warnings telling us if we need to revert problematic changes made the  
previous day.