From 81fd666b1db77b144a0346a79bdf39044325215f Mon Sep 17 00:00:00 2001
From: John-John Tedro <udoprog@tedro.se>
Date: Fri, 9 Jun 2023 08:30:42 +0200
Subject: [PATCH] Stop relying on layout of TypeId

---
 crates/rune/src/hash.rs        | 37 +++++++++++++++++++++++++++++-----
 crates/rune/src/modules/any.rs | 11 +++++-----
 2 files changed, 37 insertions(+), 11 deletions(-)

diff --git a/crates/rune/src/hash.rs b/crates/rune/src/hash.rs
index c5c6e9232..3021eb3a6 100644
--- a/crates/rune/src/hash.rs
+++ b/crates/rune/src/hash.rs
@@ -5,7 +5,6 @@ use serde::{Deserialize, Serialize};
 use std::any;
 use std::fmt;
 use std::hash::{self, BuildHasher, BuildHasherDefault, Hash as _, Hasher};
-use std::mem;
 use twox_hash::XxHash64;
 
 const SEP: u64 = 0x4bc94d6bd06053ad;
@@ -62,10 +61,38 @@ impl Hash {
     }
 
     /// Construct a hash from a type id.
-    pub const fn from_type_id(type_id: any::TypeId) -> Self {
-        // Safety: a type id is exactly a 64-bit unsigned integer.
-        // And has an identical bit pattern to `Hash`.
-        unsafe { mem::transmute(type_id) }
+    pub fn from_type_id(type_id: any::TypeId) -> Self {
+        // Note: we need to stop relying on the size of TypeId:
+        // https://github.com/rust-lang/rust/pull/109953
+        struct Capture(u64);
+
+        impl Hasher for Capture {
+            #[inline(always)]
+            fn finish(&self) -> u64 {
+                self.0
+            }
+
+            #[inline]
+            fn write_u64(&mut self, value: u64) {
+                self.0 ^= value;
+            }
+
+            #[inline]
+            fn write(&mut self, bytes: &[u8]) {
+                assert!(
+                    bytes.len() % core::mem::size_of::<u64>() == 0,
+                    "TypeId does not hash 64-bit aligned values"
+                );
+
+                for chunk in bytes.chunks_exact(8) {
+                    self.0 ^= u64::from_ne_bytes(core::array::from_fn(|n| chunk[n]));
+                }
+            }
+        }
+
+        let mut hasher = Capture(0);
+        type_id.hash(&mut hasher);
+        Self(hasher.finish())
     }
 
     /// Construct a hash to an instance function, where the instance is a
diff --git a/crates/rune/src/modules/any.rs b/crates/rune/src/modules/any.rs
index e661d17cf..ee93da573 100644
--- a/crates/rune/src/modules/any.rs
+++ b/crates/rune/src/modules/any.rs
@@ -1,18 +1,17 @@
 //! `std::any` module.
 
-use crate::runtime::{Protocol, Value};
-use crate::{Any, ContextError, Module};
-use std::any::TypeId as StdTypeId;
+use crate::runtime::{Protocol, Value, VmError};
+use crate::{Any, ContextError, Hash, Module};
 use std::fmt;
 use std::fmt::Write;
 
 #[derive(Any, Debug)]
 #[rune(module = "crate")]
 #[repr(transparent)]
-struct TypeId(StdTypeId);
+struct TypeId(Hash);
 
-fn type_id_of_val(item: Value) -> TypeId {
-    unsafe { std::mem::transmute(item.type_hash().expect("no type known for item!")) }
+fn type_id_of_val(item: Value) -> Result<TypeId, VmError> {
+    Ok(TypeId(item.type_hash()?))
 }
 
 fn format_type_id(item: &TypeId, buf: &mut String) -> fmt::Result {