extendr: Rcplx is broken on R-devel

Originally filed at https://github.com/extendr/libR-sys/issues/149.

R-devel changed the definition of Rcomplex a few days ago (https://github.com/r-devel/r-svn/commit/862f9f816ff3ff3cb3f851603f19e99f60a98475) in order to match the C representation of complex with Fortran’s representation (see https://bugs.r-project.org/show_bug.cgi?id=18430 for the details).

In short, Rcomplex is now a union, while the current exendr code assumes it’s a struct. So, now extendr won’t compile with the following error. We have to deal with this. I hope I can have time to fix this soon, but I’d appreciate if anyone can take a look because I’ve never used complex numbers…

error[E0560]: union `libR_sys::Rcomplex` has no field named `r`
  --> extendr-api\src\robj\into_robj.rs:93:20
   |
93 |         Rcomplex { r: 0., i: 0. }
   |                    ^ `libR_sys::Rcomplex` does not have this field
   |
   = note: available fields are: `__bindgen_anon_1`, `private_data_c`

error[E0560]: union `libR_sys::Rcomplex` has no field named `i`
  --> extendr-api\src\robj\into_robj.rs:93:27
   |
93 |         Rcomplex { r: 0., i: 0. }
   |                           ^ `libR_sys::Rcomplex` does not have this field
   |
   = note: available fields are: `__bindgen_anon_1`, `private_data_c`

error[E0784]: union expressions should have exactly one field
  --> extendr-api\src\robj\into_robj.rs:93:9
   |
93 |         Rcomplex { r: 0., i: 0. }
   |         ^^^^^^^^

error[E0609]: no field `r` on type `libR_sys::Rcomplex`
   --> extendr-api\src\robj\mod.rs:348:56
    |
348 |                     CPLXSXP => R_IsNA((*COMPLEX(sexp)).r) != 0,
    |                                                        ^ unknown field
    |
    = note: available fields are: `__bindgen_anon_1`, `private_data_c`
help: one of the expressions' fields has a field of the same name
    |
348 |                     CPLXSXP => R_IsNA((*COMPLEX(sexp)).__bindgen_anon_1.r) != 0,
    |                                                        +++++++++++++++++

error[E0609]: no field `r` on type `libR_sys::Rcomplex`
   --> extendr-api\src\scalar\rcplx_default.rs:105:28
    |
105 |         Rcplx(c64::new(val.r, val.i))
    |                            ^ unknown field
    |
    = note: available fields are: `__bindgen_anon_1`, `private_data_c`
help: one of the expressions' fields has a field of the same name
    |
105 |         Rcplx(c64::new(val.__bindgen_anon_1.r, val.i))
    |                            +++++++++++++++++

error[E0609]: no field `i` on type `libR_sys::Rcomplex`
   --> extendr-api\src\scalar\rcplx_default.rs:105:35
    |
105 |         Rcplx(c64::new(val.r, val.i))
    |                                   ^ unknown field
    |
    = note: available fields are: `__bindgen_anon_1`, `private_data_c`
help: one of the expressions' fields has a field of the same name
    |
105 |         Rcplx(c64::new(val.r, val.__bindgen_anon_1.i))
    |                                   +++++++++++++++++

Some errors have detailed explanations: E0560, E0609, E0784.
For more information about an error, try `rustc --explain E0560`.
error: could not compile `extendr-api` due to 6 previous errors
warning: build failed, waiting for other jobs to finish...
error: could not compile `extendr-api` due to 6 previous errors