Extended Description

From Sema::CheckForConstantInitializer:
// FIXME: Need strict checking. In C89, we need to check for
// any assignment, increment, decrement, function-calls, or
// commas outside of a sizeof. In C99, it's the same list,
// except that the aforementioned are allowed in unevaluated
// expressions. Everything else falls under the
// "may accept other forms of constant expressions" exception.
// (We never end up here for C++, so the constant expression
// rules there don't matter.)

Filing here for completeness. This is relatively low-priority because it's a non-trivial amount of work, and it's a warning nobody would care about outside of -pedantic mode.