> Keep in mind that what I wrote in my other post is an assumption.
> I assume that MAME and MESS developers build the 'other version' of their code before
> checking it in, and often or always build the combined build also. I would be
> surprised if they don't since it's kind of a fundamental rule of software development
> that you check all reasonable build flavors before submitting a change.
assumption is of course correct when you refer to developers which work on chips/components shared by both arcade and consoles/computers: usually code is already tested to be working on both projects before being added. still different devs might prefer to work in different ways: there are people working with a single binary, testing all changes in both projects at once, and there are people which first make sure that things work in MAME (or MESS, depending on which side makes more extensive use of the component being worked on), and when the code is good enough for these they pass to test the changes on the other side.
anyway, it's very easy to have regressions crawling in, no matter if you use combined builds or split ones: when you touch a component shared by many systems (say ~100 different arcade and home systems), you cannot really test *all* of them extensively... you select the systems you think are good testcases and you cross your fingers that nothing else breaks in the others. and here it enters the importance of having regular updates (and even a public git mirror) for people to test changes and report possible regressions.
if a regression appears in some untested system/game, then you have a new testcase to add for next time you work on that component
the whole thing, anyway, has not much to do with the availability of an official combined exe, though, which I thought was the subject of the thread...
developers already knows how to build their own combined build, if they want to, since they already compile their own code and a combined build only requires to add 3 simple files which just include mame.mak/mess.mak/mame.lst/mess.lst...