Add stable_hash.

CHANGELOG.md

@@ -4,6 +4,11 @@ Rhai Release Notes
 Version 1.11.0
 ==============
 
+New features
+------------
+
+* A new feature flag, `stable_hash`, is added that forces hashing to be consistent using a fixed seed.
+
 Enhancements
 ------------
 

Cargo.toml

@@ -62,6 +62,7 @@ metadata = ["serde", "serde_json", "rhai_codegen/metadata", "smartstring/serde"]
 internals = []                  # expose internal data structures
 debugging = ["internals"]       # enable debugging
 serde = ["dep:serde", "smartstring/serde", "smallvec/serde"] # implement serde for rhai types
+stable_hash = []                # perform all hashing with fixed seed value
 
 # compiling for no-std
 no_std = ["no-std-compat", "num-traits/libm", "core-error", "libm", "ahash/compile-time-rng", "hashbrown/ahash-compile-time-rng"]

src/func/hashing.rs

@@ -74,7 +74,11 @@ impl BuildHasher for StraightHasherBuilder {
 #[inline(always)]
 #[must_use]
 pub fn get_hasher() -> ahash::AHasher {
+    if cfg!(feature = "stable_hash") {
+        ahash::RandomState::with_seeds(42, 999, 123, 0).build_hasher()
+    } else {
         ahash::AHasher::default()
+    }
 }
 
 /// Calculate a non-zero [`u64`] hash key from a namespace-qualified variable name.