Better type_eq (#2946)

* typeid that doesn't suck

* actually, that's not const!

* format, move phantomdata to alloc feature block

* a

---------

Co-authored-by: Dongjia "toka" Zhang <[email protected]>

Author: addisoncrump

Cargo.toml

@@ -120,6 +120,7 @@ strum = "0.26.3"
 strum_macros = "0.26.4"
 toml = "0.8.19" # For parsing the injections toml file
 typed-builder = "0.20.0" # Implement the builder pattern at compiletime
+typeid = "1.0.0" # Safe type_eq that doesn't rely on std specialization
 uuid = { version = "1.10.0", features = ["serde", "v4"] }
 which = "6.0.3"
 windows = "0.59.0"

libafl_bolts/Cargo.toml

@@ -122,6 +122,7 @@ rustversion = { workspace = true }
 [dependencies]
 libafl_derive = { workspace = true, default-features = true, optional = true }
 static_assertions = { workspace = true }
+typeid = { workspace = true }
 
 tuple_list = { version = "0.1.3" }
 hashbrown = { workspace = true, features = [

libafl_bolts/src/tuples.rs

@@ -6,9 +6,10 @@ use alloc::{borrow::Cow, vec::Vec};
 use core::{
     any::type_name,
     fmt::{Debug, Formatter},
+    marker::PhantomData,
     ops::{Deref, DerefMut, Index, IndexMut},
 };
-use core::{any::TypeId, cell::Cell, marker::PhantomData, mem::transmute};
+use core::{any::TypeId, mem::transmute};
 
 #[cfg(feature = "alloc")]
 use serde::{Deserialize, Serialize};
@@ -21,36 +22,9 @@ use crate::HasLen;
 use crate::Named;
 
 /// Returns if the type `T` is equal to `U`, ignoring lifetimes.
-#[inline] // this entire call gets optimized away :)
 #[must_use]
 pub fn type_eq<T: ?Sized, U: ?Sized>() -> bool {
-    // decider struct: hold a cell (which we will update if the types are unequal) and some
-    // phantom data using a function pointer to allow for Copy to be implemented
-    struct W<'a, T: ?Sized, U: ?Sized>(&'a Cell<bool>, PhantomData<fn() -> (&'a T, &'a U)>);
-
-    // default implementation: if the types are unequal, we will use the clone implementation
-    impl<T: ?Sized, U: ?Sized> Clone for W<'_, T, U> {
-        #[inline]
-        fn clone(&self) -> Self {
-            // indicate that the types are unequal
-            // unfortunately, use of interior mutability (Cell) makes this not const-compatible
-            // not really possible to get around at this time
-            self.0.set(false);
-            W(self.0, self.1)
-        }
-    }
-
-    // specialized implementation: Copy is only implemented if the types are the same
-    #[expect(clippy::mismatching_type_param_order)]
-    impl<T: ?Sized> Copy for W<'_, T, T> {}
-
-    let detected = Cell::new(true);
-    // [].clone() is *specialized* in core.
-    // Types which implement copy will have their copy implementations used, falling back to clone.
-    // If the types are the same, then our clone implementation (which sets our Cell to false)
-    // will never be called, meaning that our Cell's content remains true.
-    let res = [W::<T, U>(&detected, PhantomData)].clone();
-    res[0].0.get()
+    typeid::of::<T>() == typeid::of::<U>()
 }
 
 /// Borrow each member of the tuple
@@ -955,8 +929,6 @@ mod test {
     }
 
     #[test]
-    #[cfg(feature = "alloc")]
-    #[expect(unused_qualifications)] // for type name tests
     fn test_type_eq() {
         // An alias for equality testing
         type OwnedMutSliceAlias<'a> = OwnedMutSlice<'a, u8>;
@@ -976,15 +948,6 @@ mod test {
         // test weirder lifetime things
         assert!(type_eq::<OwnedMutSlice<u8>, OwnedMutSlice<u8>>());
         assert!(!type_eq::<OwnedMutSlice<u8>, OwnedMutSlice<u32>>());
-
-        assert!(type_eq::<
-            OwnedMutSlice<u8>,
-            crate::ownedref::OwnedMutSlice<u8>,
-        >());
-        assert!(!type_eq::<
-            OwnedMutSlice<u8>,
-            crate::ownedref::OwnedMutSlice<u32>,
-        >());
     }
 
     #[test]