Joseph,
this is another revised series for the C23 rules for type compatibility. 1/4 c23: tag compatibility rules for struct and unions 2/4 c23: tag compatibility rules for enums 3/4 c23: aliasing of compatible tagged types 4/4 c23: construct composite type for tagged types The first two were revised to address the nesting (and other) issues you pointed out. For 3 and 4 I only changed c2x to c23 and moved some tests around. 3 wasn't reviewed so far and 4 still needs some more work from my side. Bootstrapped and regression tested on x86_64. Martin