Implement encode for optional function pointers

Author: madsmtm

objc2-encode/CHANGELOG.md

@@ -10,6 +10,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * `Encoding::equivalent_to`, `Encoding::equivalent_to_str` and
   `Encoding::equivalent_to_start_of_str` methods for more precise comparison
   semantics.
+* Added `Encode` and `RefEncode` implementations for `Option` function
+  pointers.
 
 ### Changed
 * Discourage comparing `str` with `Encoding` using `PartialEq`. This trait

objc2-encode/src/encode.rs

@@ -408,10 +408,16 @@ macro_rules! encode_fn_pointer_impl {
         unsafe impl<Ret: Encode, $($Arg: Encode),*> Encode for $FnTy {
             const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Unknown);
         }
-
         unsafe impl<Ret: Encode, $($Arg: Encode),*> RefEncode for $FnTy {
             const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
         }
+
+        unsafe impl<Ret: Encode, $($Arg: Encode),*> Encode for Option<$FnTy> {
+            const ENCODING: Encoding<'static> = Encoding::Pointer(&Encoding::Unknown);
+        }
+        unsafe impl<Ret: Encode, $($Arg: Encode),*> RefEncode for Option<$FnTy> {
+            const ENCODING_REF: Encoding<'static> = Encoding::Pointer(&Self::ENCODING);
+        }
     };
     ($($Arg: ident),+) => {
         // Normal functions
@@ -543,5 +549,9 @@ mod tests {
             <extern "C" fn(x: ()) -> ()>::ENCODING,
             Encoding::Pointer(&Encoding::Unknown)
         );
+        assert_eq!(
+            <Option<unsafe extern "C" fn()>>::ENCODING,
+            Encoding::Pointer(&Encoding::Unknown)
+        );
     }
 }

objc2/src/runtime.rs

@@ -595,7 +595,7 @@ impl fmt::Debug for Object {
 mod tests {
     use alloc::string::ToString;
 
-    use super::{Bool, Class, Ivar, Method, Object, Protocol, Sel};
+    use super::{Bool, Class, Imp, Ivar, Method, Object, Protocol, Sel};
     use crate::test_utils;
     use crate::Encode;
 
@@ -701,6 +701,8 @@ mod tests {
         assert_eq!(<*mut Object>::ENCODING.to_string(), "@");
         assert_eq!(<&Class>::ENCODING.to_string(), "#");
         assert_eq!(Sel::ENCODING.to_string(), ":");
+        assert_eq!(Imp::ENCODING.to_string(), "^?");
+        assert_eq!(<Option<Imp>>::ENCODING.to_string(), "^?");
     }
 
     #[test]