[Rd] Breaking Change in Rcomplex Layout?

[Michael Milton]

Hi all,

There seems to have been a breaking change in the R trunk caused by a fix
to bug 18430 <https://bugs.r-project.org/show_bug.cgi?id=18430> that
relates to the layout of the Rcomplex typedef. Previously it was a struct,
but now it's a union by default
<https://github.com/r-devel/r-svn/commit/862f9f816ff3ff3cb3f851603f19e99f60a98475#diff-e9b09a44d9dc69444eca2300325e790a0cc6d2c8c3960f47519c7f8ef896f9e4>,
which breaks downstream code that relied on this layout. I'm aware of
the R_LEGACY_RCOMPLEX variable, but I still wouldn't expect an unreported
breaking change especially if it's aimed at R 4.3 (although I'm not sure if
it is). I believe src/include/R_ext/Complex.h, which this patch affects, is
considered part of the public R ABI since it's included by R.h.

What should I, as a downstream package developer, do about this change?

Cheers.

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