Eric Botcazou wrote:
Generally speaking, this occurs as follows: a patch happens to break an extension because GCC has (had?) so many extensions that it is nearly impossible to foresee all the side-effects a patch will have on them. Then somebody notices the breakage and complains about it, and sometimes even writes a patch to undo the breakage (typically an Apple employee, because Apple is legitimately concerned about backwards compatibility). Then the patch is knocked down by the language lawyers who are floating around because, see, if the extension was broken, it probably deserved it as it was under-specified and, consequently, cannot be anything else than an abomination.
SOurce compatibility is definitely a very important criterion in new releases. In the GNAT world, we have a few times run into cases of constructs which were accepted by GNAT, but which on more careful examination of the standard, turned out should have been rejected. Even in such cases, where there is from a language lawyer point of view a clear bug, we are reluctant to introduce source incompatibilities if there is no obvious work around which applies in all cases. Sometimes we have made errors warnings for one release to ease the transition, or provided a debug switch to get the old (wrong) behavior.
