Add windows_legacy opt-in backend (#724)

Some users may prefer to use the legacy Windows backend (e.g. see #723),
so I think it's worth to introduce a documented configuration flag for
it and replace the undocumented `getrandom_windows_legacy` flag.

Author: newpavlov

CHANGELOG.md

@@ -6,18 +6,26 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [0.3.4] - UNRELEASED
 
-### Changed
-- Relax MSRV for the `linux_raw` opt-in backend on ARM targets [#688]
-
 ### Added
 - `unsupported` opt-in backend [#667]
+- `windows_legacy` opt-in backend [#724]
+
+### Changed
+- Implement Memory Sanitizer unpoisoning more precisely [#678]
+- Relax MSRV for the `linux_raw` opt-in backend on ARM targets [#688]
+- Use `getrandom` syscall on all RISC-V Linux targets [#699]
+- Replaced `wasi` dependency with `wasip2` [#721]
 
 ### Removed
 - Unstable `rustc-dep-of-std` crate feature [#694]
 
 [#667]: https://github.com/rust-random/getrandom/pull/667
+[#678]: https://github.com/rust-random/getrandom/pull/678
 [#688]: https://github.com/rust-random/getrandom/pull/688
 [#694]: https://github.com/rust-random/getrandom/pull/694
+[#699]: https://github.com/rust-random/getrandom/pull/699
+[#721]: https://github.com/rust-random/getrandom/pull/721
+[#724]: https://github.com/rust-random/getrandom/pull/724
 
 ## [0.3.3] - 2025-05-09
 

Cargo.lock

@@ -77,9 +77,8 @@ wasm-bindgen-test = "0.3"
 [lints.rust.unexpected_cfgs]
 level = "warn"
 check-cfg = [
-  'cfg(getrandom_backend, values("custom", "efi_rng", "rdrand", "rndr", "linux_getrandom", "linux_raw", "wasm_js", "unsupported"))',
+  'cfg(getrandom_backend, values("custom", "efi_rng", "rdrand", "rndr", "linux_getrandom", "linux_raw", "wasm_js", "windows_legacy", "unsupported"))',
   'cfg(getrandom_msan)',
-  'cfg(getrandom_windows_legacy)',
   'cfg(getrandom_test_linux_fallback)',
   'cfg(getrandom_test_linux_without_fallback)',
   'cfg(getrandom_test_netbsd_fallback)',

Cargo.toml

@@ -86,6 +86,7 @@ of randomness based on their specific needs:
 | `rndr`            | AArch64              | `aarch64-*`              | [`RNDR`] register
 | `wasm_js`         | Web Browser, Node.js | `wasm32‑unknown‑unknown`, `wasm32v1-none` | [`Crypto.getRandomValues`]. Requires feature `wasm_js` ([see below](#webassembly-support)).
 | `efi_rng`         | UEFI                 | `*-unknown‑uefi`         | [`EFI_RNG_PROTOCOL`] with `EFI_RNG_ALGORITHM_RAW` (requires `std` and Nightly compiler)
+| `windows_legacy`  | Windows              | `*-windows-*`            | [`RtlGenRandom`]
 | `custom`          | All targets          | `*`                      | User-provided custom implementation (see [custom backend])
 | `unsupported`     | All targets          | `*`                      | Always returns `Err(Error::UNSUPPORTED)` (see [unsupported backend])
 

README.md

@@ -48,7 +48,7 @@ fn main() {
 
         match rustc_minor_version() {
             Some(minor_ver) if minor_ver < WIN7_INTRODUCED_MINOR_VER => {
-                println!("cargo:rustc-cfg=getrandom_windows_legacy");
+                println!("cargo:rustc-cfg=getrandom_backend=\"windows_legacy\"");
             }
             None => println!("cargo:warning=Couldn't detect minor version of the Rust compiler"),
             _ => {}

build.rs

@@ -28,6 +28,9 @@ cfg_if! {
     } else if #[cfg(getrandom_backend = "efi_rng")] {
         mod efi_rng;
         pub use efi_rng::*;
+    } else if #[cfg(getrandom_backend = "windows_legacy")] {
+        mod windows_legacy;
+        pub use windows_legacy::*;
     } else if #[cfg(all(getrandom_backend = "wasm_js"))] {
         cfg_if! {
             if #[cfg(feature = "wasm_js")] {
@@ -173,9 +176,9 @@ cfg_if! {
     } else if #[cfg(target_os = "solid_asp3")] {
         mod solid;
         pub use solid::*;
-    } else if #[cfg(all(windows, any(target_vendor = "win7", getrandom_windows_legacy)))] {
-        mod windows7;
-        pub use windows7::*;
+    } else if #[cfg(all(windows, target_vendor = "win7"))] {
+        mod windows_legacy;
+        pub use windows_legacy::*;
     } else if #[cfg(windows)] {
         mod windows;
         pub use windows::*;

src/backends.rs

@@ -14,6 +14,9 @@ use core::{ffi::c_void, mem::MaybeUninit};
 
 pub use crate::util::{inner_u32, inner_u64};
 
+#[cfg(not(windows))]
+compile_error!("`windows_legacy` backend can be enabled only for Windows targets!");
+
 // Binding to the Windows.Win32.Security.Authentication.Identity.RtlGenRandom
 // API. Don't use windows-targets as it doesn't support Windows 7 targets.
 #[link(name = "advapi32")]