Use zero for no hash.

src/ast.rs

@@ -1,6 +1,7 @@
 //! Module defining the AST (abstract syntax tree).
 
 use crate::calc_fn_hash;
+use crate::func::hashing::DEFAULT_HASH;
 use crate::module::NamespaceRef;
 use crate::tokenizer::Token;
 use crate::types::dynamic::Union;
@@ -1801,7 +1802,7 @@ impl OpAssignment<'_> {
 pub struct FnCallHashes {
     /// Pre-calculated hash for a script-defined function ([`None`] if native functions only).
     #[cfg(not(feature = "no_function"))]
-    pub script: Option<u64>,
+    pub script: u64,
     /// Pre-calculated hash for a native Rust function with no parameter types.
     pub native: u64,
 }
@@ -1809,11 +1810,11 @@ pub struct FnCallHashes {
 impl fmt::Debug for FnCallHashes {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         #[cfg(not(feature = "no_function"))]
-        if let Some(script) = self.script {
-            return if script == self.native {
+        if self.script != 0 {
+            return if self.script == self.native {
                 fmt::Debug::fmt(&self.native, f)
             } else {
-                write!(f, "({}, {})", script, self.native)
+                write!(f, "({}, {})", self.script, self.native)
             };
         }
 
@@ -1824,9 +1825,11 @@ impl fmt::Debug for FnCallHashes {
 impl From<u64> for FnCallHashes {
     #[inline(always)]
     fn from(hash: u64) -> Self {
+        let hash = if hash == 0 { DEFAULT_HASH } else { hash };
+
         Self {
             #[cfg(not(feature = "no_function"))]
-            script: Some(hash),
+            script: hash,
             native: hash,
         }
     }
@@ -1839,8 +1842,8 @@ impl FnCallHashes {
     pub const fn from_native(hash: u64) -> Self {
         Self {
             #[cfg(not(feature = "no_function"))]
-            script: None,
-            native: hash,
+            script: 0,
+            native: if hash == 0 { DEFAULT_HASH } else { hash },
         }
     }
     /// Create a [`FnCallHashes`] with both native Rust and script function hashes.
@@ -1849,8 +1852,8 @@ impl FnCallHashes {
     pub const fn from_all(#[cfg(not(feature = "no_function"))] script: u64, native: u64) -> Self {
         Self {
             #[cfg(not(feature = "no_function"))]
-            script: Some(script),
-            native,
+            script: if script == 0 { DEFAULT_HASH } else { script },
+            native: if native == 0 { DEFAULT_HASH } else { native },
         }
     }
     /// Is this [`FnCallHashes`] native Rust only?
@@ -1858,7 +1861,7 @@ impl FnCallHashes {
     #[must_use]
     pub const fn is_native_only(&self) -> bool {
         #[cfg(not(feature = "no_function"))]
-        return self.script.is_none();
+        return self.script == 0;
 
         #[cfg(feature = "no_function")]
         return true;

src/func/call.rs

@@ -177,6 +177,10 @@ impl Engine {
         allow_dynamic: bool,
         is_op_assignment: bool,
     ) -> Option<&'s FnResolutionCacheEntry> {
+        if hash_script == 0 {
+            return None;
+        }
+
         let fn_name = fn_name.as_ref();
 
         let mut hash = args.as_ref().map_or(hash_script, |args| {
@@ -562,13 +566,10 @@ impl Engine {
 
         // Scripted function call?
         #[cfg(not(feature = "no_function"))]
-        let hash_script = hashes.script;
-
-        #[cfg(not(feature = "no_function"))]
-        if let Some(FnResolutionCacheEntry { func, source }) = hash_script.and_then(|hash| {
-            self.resolve_fn(mods, state, lib, fn_name, hash, None, false, false)
-                .cloned()
-        }) {
+        if let Some(FnResolutionCacheEntry { func, source }) = self
+            .resolve_fn(mods, state, lib, fn_name, hashes.script, None, false, false)
+            .cloned()
+        {
             // Script function call
             assert!(func.is_script());
 

src/func/hashing.rs

@@ -8,7 +8,13 @@ use std::{
     iter::empty,
 };
 
-/// A hasher that only takes one single [`u64`] and returns it as a hash key.
+pub const DEFAULT_HASH: u64 = 42;
+
+/// A hasher that only takes one single [`u64`] and returns it as a non-zero hash key.
+///
+/// # Zeros
+///
+/// If the value is zero, then it is mapped to `DEFAULT_HASH`.
 ///
 /// # Panics
 ///
@@ -29,6 +35,10 @@ impl Hasher for StraightHasher {
         key.copy_from_slice(bytes);
 
         self.0 = u64::from_ne_bytes(key);
+
+        if self.0 == 0 {
+            self.0 = DEFAULT_HASH
+        }
     }
 }
 
@@ -41,7 +51,7 @@ impl BuildHasher for StraightHasherBuilder {
 
     #[inline(always)]
     fn build_hasher(&self) -> Self::Hasher {
-        StraightHasher(42)
+        StraightHasher(DEFAULT_HASH)
     }
 }
 
@@ -52,11 +62,15 @@ pub fn get_hasher() -> ahash::AHasher {
     ahash::AHasher::default()
 }
 
-/// Calculate a [`u64`] hash key from a namespace-qualified variable name.
+/// Calculate a non-zero [`u64`] hash key from a namespace-qualified variable name.
 ///
 /// Module names are passed in via `&str` references from an iterator.
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
 ///
+/// # Zeros
+///
+/// If the hash happens to be zero, it is mapped to `DEFAULT_HASH`.
+///
 /// # Note
 ///
 /// The first module name is skipped.  Hashing starts from the _second_ module in the chain.
@@ -76,15 +90,23 @@ pub fn calc_qualified_var_hash<'a>(
         .for_each(|m| m.as_ref().hash(s));
     len.hash(s);
     var_name.as_ref().hash(s);
-    s.finish()
+
+    match s.finish() {
+        0 => DEFAULT_HASH,
+        r => r,
+    }
 }
 
-/// Calculate a [`u64`] hash key from a namespace-qualified function name
+/// Calculate a non-zero [`u64`] hash key from a namespace-qualified function name
 /// and the number of parameters, but no parameter types.
 ///
 /// Module names are passed in via `&str` references from an iterator.
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
 ///
+/// # Zeros
+///
+/// If the hash happens to be zero, it is mapped to `DEFAULT_HASH`.
+///
 /// # Note
 ///
 /// The first module name is skipped.  Hashing starts from the _second_ module in the chain.
@@ -106,22 +128,34 @@ pub fn calc_qualified_fn_hash(
     len.hash(s);
     fn_name.as_ref().hash(s);
     num.hash(s);
-    s.finish()
+
+    match s.finish() {
+        0 => DEFAULT_HASH,
+        r => r,
+    }
 }
 
-/// Calculate a [`u64`] hash key from a non-namespace-qualified function name
+/// Calculate a non-zero [`u64`] hash key from a non-namespace-qualified function name
 /// and the number of parameters, but no parameter types.
 ///
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
+///
+/// # Zeros
+///
+/// If the hash happens to be zero, it is mapped to `DEFAULT_HASH`.
 #[inline(always)]
 #[must_use]
 pub fn calc_fn_hash(fn_name: impl AsRef<str>, num: usize) -> u64 {
     calc_qualified_fn_hash(empty::<&str>(), fn_name, num)
 }
 
-/// Calculate a [`u64`] hash key from a list of parameter types.
+/// Calculate a non-zero [`u64`] hash key from a list of parameter types.
 ///
 /// Parameter types are passed in via [`TypeId`] values from an iterator.
+///
+/// # Zeros
+///
+/// If the hash happens to be zero, it is mapped to `DEFAULT_HASH`.
 #[inline]
 #[must_use]
 pub fn calc_fn_params_hash(params: impl Iterator<Item = TypeId>) -> u64 {
@@ -129,12 +163,23 @@ pub fn calc_fn_params_hash(params: impl Iterator<Item = TypeId>) -> u64 {
     let mut len = 0;
     params.inspect(|_| len += 1).for_each(|t| t.hash(s));
     len.hash(s);
-    s.finish()
+
+    match s.finish() {
+        0 => DEFAULT_HASH,
+        r => r,
+    }
 }
 
 /// Combine two [`u64`] hashes by taking the XOR of them.
+///
+/// # Zeros
+///
+/// If the hash happens to be zero, it is mapped to `DEFAULT_HASH`.
 #[inline(always)]
 #[must_use]
 pub const fn combine_hashes(a: u64, b: u64) -> u64 {
-    a ^ b
+    match a ^ b {
+        0 => DEFAULT_HASH,
+        r => r,
+    }
 }