Stable Hash: Add feature, adjust CI, modify build.rs, add new API for accessing and setting the ahash seed in config.rs, make config.rs public

build.template

@@ -1,7 +1,60 @@
-//! Configuration settings for this Rhai build
-//!
-//! This file is auto-generated from `build.template`
+#[cfg(feature = "stable_hash")]
+use core::cell::OnceCell;
 
+// [236,800,954,213], haha funny yume nikki reference
+
+#[cfg(not(feature = "stable_hash"))]
 /// Fixed hashing seeds for stable hashing.
+///
 /// Set to [`None`] to disable stable hashing.
-pub const AHASH_SEED: Option<[u64; 4]> = {{AHASH_SEED}};
+///
+/// See [`set_rhai_ahash_seed`] for more.
+///
+/// You can also set this at compile time by disabling `stable_hash` and setting the `RHAI_AHASH_SEED`
+/// environment variable instead.
+///
+/// E.g. `env RHAI_AHASH_SEED ="[236,800,954,213]"`
+const AHASH_SEED: Option<[u64; 4]> = {{AHASH_SEED}};
+#[cfg(feature = "stable_hash")]
+/// Fixed hashing seeds for stable hashing.
+///
+/// Set to [`None`] to disable stable hashing.
+///
+/// See [`set_rhai_ahash_seed`] for more.
+///
+/// You can also set this at compile time by disabling `stable_hash` and setting the `RHAI_AHASH_SEED`
+/// environment variable instead.
+///
+/// E.g. `env RHAI_AHASH_SEED ="[236,800,954,213]"`
+static AHASH_SEED: OnceCell<Option<[u64; 4]>> = OnceCell::new();
+
+#[cfg(feature = "stable_hash")]
+#[doc(cfg(feature = "stable_hash"))]
+/// Sets the Rhai Ahash seed. This is used to hash functions and the like.
+///
+/// This is a global variable, and thus will affect every Rhai instance.
+/// This should not be used _unless_ you know you need it.
+///
+/// **WARNING**:
+/// - You can only call this function **ONCE** for the whole of your program execution.
+/// - You should gracefully handle the `Err(())`.
+/// - You **MUST** call this before **ANY** Rhai operation occurs (e.g. creating an [`Engine`]).
+pub fn set_rhai_ahash_seed(new_seed: Option<[u64; 4]>) -> Result<(), Option<[u64; 4]>> {
+    AHASH_SEED.set(new_seed)
+}
+
+#[cfg(feature = "stable_hash")]
+/// Gets the current Rhai Ahash Seed.
+///
+/// See [`set_rhai_ahash_seed`] for more.
+pub fn get_rhai_ahash_seed() -> Option<[u64; 4]> {
+    AHASH_SEED.get().map(|x| *x).flatten()
+}
+
+#[cfg(not(feature = "stable_hash"))]
+/// Gets the current Rhai Ahash Seed.
+///
+/// See [`AHASH_SEED`] and [`set_rhai_ahash_seed`] for more.
+pub fn get_rhai_ahash_seed() -> Option<[u64; 4]> {
+    AHASH_SEED
+}