Hi again,

I managed to spend much more time on the issue and I'm starting a new 
thread with a mature - IMHO - proposal: the big thing is the use of the 
existing check_array_designated_initializer in 
process_init_constructor_array,  which calls maybe_constant_value, as we 
want, and covers all the ill-formed cases which I can imagine. I'm also 
tweaking a bit the parser to check the return value of 
require_potential_rvalue_constant_expression in order to avoid redundant 
diagnostic in some cases. Also, a couple more testcases beyond the bug 
report.

Tested x86_64-linux.

Thanks, Paolo.

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