oxifft 0.2.0

Pure Rust implementation of FFTW - the Fastest Fourier Transform in the West
Documentation 
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//! `OxiFFT` build script.
//!
//! This build script emits compile-time warnings when features that introduce
//! C or Fortran dependencies are enabled, so downstream users are aware that
//! those features break the "Pure Rust" guarantee.

fn main() {
    // Detect features that pull in C/Fortran dependencies and warn the user.
    let mpi_enabled = std::env::var("CARGO_FEATURE_MPI").is_ok();
    let sve_enabled = std::env::var("CARGO_FEATURE_SVE").is_ok();

    if mpi_enabled {
        println!(
            "cargo:warning=\
oxifft: the `mpi` feature links against the system MPI library (C/Fortran), \
which violates the Pure Rust policy for default builds. \
This feature is provided for distributed computing and is explicitly \
feature-gated. No pure-Rust MPI implementation currently exists. \
See https://github.com/cool-japan/oxifft/blob/master/README.md#mpi for details."
        );
    }

    if sve_enabled {
        println!(
            "cargo:warning=\
oxifft: the `sve` feature uses the `libc` crate for ARM SVE HWCAP detection. \
`libc` itself is pure Rust (it uses inline assembly / syscalls), but it \
provides C-compatible types and is considered a C-boundary crate. \
A future release will replace this with `std::arch` when SVE intrinsics \
stabilise in the Rust standard library."
        );
    }
}