efriedma-quic wrote:
The primary problem with allowing flexible arrays alone in structs/unions is
that you end up with a zero-size type. This leads to weird semantic issues
because standard C/C++ doesn't have any provision for zero-size types: pointer
arithmetic, struct layout, and initialization aren't well-defined when
zero-size types are involved. Because we support zero-length arrays/empty
structs as an extension, we have some solution for some of these cases, but
some of the edge cases just explode. (And there's no guidance from the
standard because the standard doesn't allow this in the first place.)
Something like `union U { int x, y[]; };` doesn't run into those issues,
though; the expected semantics are pretty unambigious.
https://github.com/llvm/llvm-project/pull/84428
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