Make less-safe work on espidf

Cargo.toml

@@ -183,6 +183,7 @@ default = ["alloc", "dev_urandom_fallback"]
 alloc = []
 dev_urandom_fallback = []
 less-safe-getrandom-custom-or-rdrand = []
+less-safe-getrandom-espidf = []
 slow_tests = []
 std = ["alloc"]
 unstable-testing-arm-no-hw = []

src/lib.rs

@@ -32,6 +32,14 @@
 //!         </a> and <a href="https://docs.rs/getrandom/0.2.10/getrandom/#rdrand-on-x86">
 //!             RDRAND on x86
 //!         </a> for additional details.
+//! <tr><td><code>less-safe-getrandom-espidf</code>
+//!     <td>Treat getrandom as a secure random number generator (see
+//!         <code>SecureRandom</code>) on the esp-idf target. While the esp-idf
+//!         target does have hardware RNG, it is beyond the scope of ring to
+//!         ensure its configuration. This feature allows ring to build
+//!         on esp-idf despite the liklihood that RNG is not secure.
+//!         This feature only works with <code>os = espidf</code> targets.
+//!         See <a href="https://docs.espressif.com/projects/esp-idf/en/stable/esp32/api-reference/system/random.html">
 //! <tr><td><code>std</code>
 //!     <td>Enable features that use libstd, in particular
 //!         <code>std::error::Error</code> integration. Implies `alloc`.

src/rand.rs

@@ -126,6 +126,7 @@ impl crate::sealed::Sealed for SystemRandom {}
 // implementation.
 #[cfg(any(
     all(feature = "less-safe-getrandom-custom-or-rdrand", target_os = "none"),
+    all(feature = "less-safe-getrandom-espidf", target_os = "espidf"),
     target_os = "aix",
     target_os = "android",
     target_os = "dragonfly",