crates/fayalite/src/module.rs

@@ -2396,16 +2396,13 @@ impl ModuleBuilder {
     #[track_caller]
     pub fn extern_module_simulation_fn<
         Args: fmt::Debug + Clone + Hash + Eq + Send + Sync + 'static,
-        F: Copy + Fn(Args, crate::sim::ExternModuleSimulationState) -> Fut + Send + Sync + 'static,
         Fut: IntoFuture<Output = ()> + 'static,
     >(
         &self,
         args: Args,
-        f: F,
+        f: fn(Args, crate::sim::ExternModuleSimulationState) -> Fut,
     ) {
-        // use for compile-time side-effect
-        let _ = crate::sim::SimGeneratorFn::<Args, F, Fut>::ASSERT_F_IS_ZERO_SIZED;
-        self.extern_module_simulation(crate::sim::SimGeneratorFn::new(args, f));
+        self.extern_module_simulation(crate::sim::SimGeneratorFn { args, f });
     }
 }
 

crates/fayalite/src/sim.rs

@@ -54,6 +54,7 @@ use std::{
     hash::Hash,
     mem,
     pin::{Pin, pin},
+    ptr,
     rc::Rc,
     sync::{Arc, Mutex, MutexGuard},
     task::Poll,
@@ -4064,48 +4065,13 @@ pub trait ExternModuleSimGenerator: Clone + Eq + Hash + Any + Send + Sync + fmt:
     fn run<'a>(&'a self, sim: ExternModuleSimulationState) -> impl IntoFuture<Output = ()> + 'a;
 }
 
-/// Type requirements: `F` must be zero-sized, this guarantees that the function called
-/// by `F` is entirely determined by the type `F` and not by its value, allowing us to
-/// correctly leave `F` out of the stuff used for `Hash` and `Eq`.
-///
-/// Note we can't just use function pointers instead -- comparing them is non-deterministic
-/// since Rust will duplicate and/or merge functions, even if those functions happen to have
-/// different UB but just happen to compile to the same assembly language:
-/// <https://github.com/rust-lang/unsafe-code-guidelines/issues/589#issuecomment-3515424930>
-pub struct SimGeneratorFn<Args, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> {
-    args: Args,
-    f: F,
+pub struct SimGeneratorFn<Args, Fut> {
+    pub args: Args,
+    pub f: fn(Args, ExternModuleSimulationState) -> Fut,
 }
 
-impl<Args, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut>
-    SimGeneratorFn<Args, F, Fut>
-{
-    pub const ASSERT_F_IS_ZERO_SIZED: () = {
-        if size_of::<F>() != 0 {
-            panic!(
-                "F must be zero-sized -- so it must be a closure with no captures or a function item, it can't be a function pointer"
-            );
-        }
-    };
-    pub const fn new(args: Args, f: F) -> Self {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
-        Self { args, f }
-    }
-    pub const fn args(&self) -> &Args {
-        &self.args
-    }
-    pub const fn f(&self) -> F {
-        self.f
-    }
-}
-
-impl<Args: fmt::Debug, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> fmt::Debug
-    for SimGeneratorFn<Args, F, Fut>
-{
+impl<Args: fmt::Debug, Fut> fmt::Debug for SimGeneratorFn<Args, Fut> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
         let Self { args, f: _ } = self;
         f.debug_struct("SimGeneratorFn")
             .field("args", args)
@@ -4114,39 +4080,25 @@ impl<Args: fmt::Debug, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, F
     }
 }
 
-impl<Args: Hash, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> Hash
-    for SimGeneratorFn<Args, F, Fut>
-{
+impl<Args: Hash, Fut> Hash for SimGeneratorFn<Args, Fut> {
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
-        let Self { args, f: _ } = self;
+        let Self { args, f } = self;
         args.hash(state);
+        f.hash(state);
     }
 }
 
-impl<Args: Eq, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> Eq
-    for SimGeneratorFn<Args, F, Fut>
-{
-}
+impl<Args: Eq, Fut> Eq for SimGeneratorFn<Args, Fut> {}
 
-impl<Args: PartialEq, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> PartialEq
-    for SimGeneratorFn<Args, F, Fut>
-{
+impl<Args: PartialEq, Fut> PartialEq for SimGeneratorFn<Args, Fut> {
     fn eq(&self, other: &Self) -> bool {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
-        let Self { args, f: _ } = self;
-        *args == other.args
+        let Self { args, f } = self;
+        *args == other.args && ptr::fn_addr_eq(*f, other.f)
     }
 }
 
-impl<Args: Clone, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> Clone
-    for SimGeneratorFn<Args, F, Fut>
-{
+impl<Args: Clone, Fut> Clone for SimGeneratorFn<Args, Fut> {
     fn clone(&self) -> Self {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
         Self {
             args: self.args.clone(),
             f: self.f,
@@ -4154,20 +4106,14 @@ impl<Args: Clone, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> C
     }
 }
 
-impl<Args: Copy, F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut, Fut> Copy
-    for SimGeneratorFn<Args, F, Fut>
-{
-}
+impl<Args: Copy, Fut> Copy for SimGeneratorFn<Args, Fut> {}
 
 impl<
-    Args: fmt::Debug + Clone + Eq + Hash + Send + Sync + 'static,
-    F: Copy + Fn(Args, ExternModuleSimulationState) -> Fut + Send + Sync + 'static,
+    T: fmt::Debug + Clone + Eq + Hash + Send + Sync + 'static,
     Fut: IntoFuture<Output = ()> + 'static,
-> ExternModuleSimGenerator for SimGeneratorFn<Args, F, Fut>
+> ExternModuleSimGenerator for SimGeneratorFn<T, Fut>
 {
     fn run<'a>(&'a self, sim: ExternModuleSimulationState) -> impl IntoFuture<Output = ()> + 'a {
-        // use for compile-time side-effect
-        let _ = Self::ASSERT_F_IS_ZERO_SIZED;
         (self.f)(self.args.clone(), sim)
     }
 }