Backport cygwin support

CHANGELOG.md

@@ -4,6 +4,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.2.16] - 2025-04-22
+### Added
+- Backport cygwin support [#654]
+
+[#654]: https://github.com/rust-random/getrandom/pull/654
+
 ## [0.2.15] - 2024-05-06
 ### Added
 - Apple visionOS support [#410]

src/lib.rs

@@ -30,6 +30,7 @@
 //! | PS Vita           | `*-vita-*`         | [`getentropy`][13]
 //! | QNX Neutrino      | `*‑nto-qnx*`       | [`/dev/urandom`][14] (identical to `/dev/random`)
 //! | AIX               | `*-ibm-aix`        | [`/dev/urandom`][15]
+//! | Cygwin            | `*-cygwin`         | [`getrandom`][19] (based on [`RtlGenRandom`])
 //!
 //! Pull Requests that add support for new targets to `getrandom` are always welcome.
 //!
@@ -181,8 +182,10 @@
 //! [16]: https://man.netbsd.org/getrandom.2
 //! [17]: https://www.gnu.org/software/libc/manual/html_mono/libc.html#index-getrandom
 //! [18]: https://github.com/rust3ds/shim-3ds/commit/b01d2568836dea2a65d05d662f8e5f805c64389d
+//! [19]: https://github.com/cygwin/cygwin/blob/main/winsup/cygwin/libc/getentropy.cc
 //!
 //! [`BCryptGenRandom`]: https://docs.microsoft.com/en-us/windows/win32/api/bcrypt/nf-bcrypt-bcryptgenrandom
+//! [`RtlGenRandom`]: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
 //! [`Crypto.getRandomValues`]: https://www.w3.org/TR/WebCryptoAPI/#Crypto-method-getRandomValues
 //! [`RDRAND`]: https://software.intel.com/en-us/articles/intel-digital-random-number-generator-drng-software-implementation-guide
 //! [`CCRandomGenerateBytes`]: https://opensource.apple.com/source/CommonCrypto/CommonCrypto-60074/include/CommonRandom.h.auto.html
@@ -251,6 +254,7 @@ cfg_if! {
         // Check for target_arch = "arm" to only include the 3DS. Does not
         // include the Nintendo Switch (which is target_arch = "aarch64").
         all(target_os = "horizon", target_arch = "arm"),
+        target_os = "cygwin",
     ))] {
         mod util_libc;
         #[path = "getrandom.rs"] mod imp;

src/util_libc.rs

@@ -9,7 +9,7 @@ use core::{
 use libc::c_void;
 
 cfg_if! {
-    if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android"))] {
+    if #[cfg(any(target_os = "netbsd", target_os = "openbsd", target_os = "android", target_os = "cygwin"))] {
         use libc::__errno as errno_location;
     } else if #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "hurd", target_os = "redox", target_os = "dragonfly"))] {
         use libc::__errno_location as errno_location;