docs(s2n-quic): update doc to indicate it works with s2n-tls on Windows

README.md

@@ -27,7 +27,12 @@ See the [API documentation](https://docs.rs/s2n-quic), [examples](https://github
 s2n-quic = "1"
 ```
 
-**NOTE**: On unix-like systems, [`s2n-tls`](https://github.com/aws/s2n-tls) will be used as the default TLS provider.
+**NOTE**: The default TLS provider depends on the platform. On unix-like systems, and on Windows
+when building with the GNU/MinGW toolchain, [`s2n-tls`](https://github.com/aws/s2n-tls) is used as
+the default TLS provider. On Windows with the MSVC toolchain,
+[`rustls`](https://crates.io/crates/rustls) is the default, because `s2n-tls` does not build with
+MSVC.
+
 On linux systems, [`aws-lc-rs`](https://github.com/awslabs/aws-lc-rs) will be used for cryptographic
 operations. A C compiler and CMake may be required on these systems for installation.
 

quic/s2n-quic-tests/README.md

@@ -12,17 +12,23 @@ To further increase performance, the tests are contained within the `src` folder
 
 ### Platform-specific Tests
 
-Some tests in this crate are platform-specific, particularly those that depend on s2n-tls, which is only available on Unix systems. These tests are conditionally compiled using `cfg[unix]` attributes. For example:
+Some tests in this crate are platform-specific. Most notably, tests that depend on the s2n-tls provider are gated on the `s2n_tls_provider` cfg, which the crate's `build.rs` emits on the targets where s2n-tls builds: unix and Windows with the GNU/MinGW toolchain (but not MSVC). For example:
 
 ```rust
+// Needs the s2n-tls provider (mTLS, the ClientHelloCallback trait, session resumption).
+#[cfg(s2n_tls_provider)]
+mod mtls;
+
+// The s2n-tls `fips` feature depends on aws-lc-fips-sys, which does not build on Windows MinGW.
 #[cfg(unix)]
-mod resumption;
+mod fips;
 
+// Uses real OS sockets, which conflict with bach's simulated time on Windows.
 #[cfg(not(target_os = "windows"))]
-mod mtls;
+mod prioritized_socket;
 ```
 
-This approach ensures that tests only run on platforms where their dependencies are available. The Cargo.toml file also includes platform-specific dependencies to support this.
+This ensures tests only build on platforms where their dependencies are available. `Cargo.toml` gates the s2n-tls dependencies to the same targets; keep those in sync with the `s2n_tls_provider` cfg in `build.rs`.
 
 ## Test Structure
 

quic/s2n-quic/src/lib.rs

@@ -34,7 +34,8 @@
 //! _Enabled by default_
 //!
 //! Enables platform detection for the recommended implementation of TLS. Currently, this uses
-//! [`s2n-tls`][s2n-tls] on unix-like platforms and [`rustls`][rustls] on everything else.
+//! [`s2n-tls`][s2n-tls] on unix-like platforms and on Windows with the GNU/MinGW toolchain, and
+//! [`rustls`][rustls] on everything else (notably Windows with the MSVC toolchain).
 //!
 //! ### `provider-tls-rustls`
 //!
@@ -50,6 +51,8 @@
 //!
 //! **NOTE**: this will override the platform detection and always use [`s2n-tls`][s2n-tls] by default.
 //!
+//! **NOTE**: on Windows, [`s2n-tls`][s2n-tls] only builds with the GNU/MinGW toolchain it does not build with the MSVC toolchain.
+//!
 //! ### `provider-tls-fips`
 //!
 //! **FIPS mode with `provider-tls-s2n`**