Introduce ByteOrder::try_map

crates/asm/src/lib.rs

@@ -142,20 +142,22 @@ pub mod musli_zerocopy_swap {
     pub struct Struct {
         bits32: u32,
         bits64: u64,
+        bits128: u128,
+        array: [u8; 16],
     }
 
     #[inline(never)]
-    pub fn ensure_struct_native(st: Struct) -> Struct {
+    pub fn ensure_struct_ne(st: Struct) -> Struct {
         st.swap_bytes::<endian::Native>()
     }
 
     #[inline(never)]
-    pub fn ensure_struct_little(st: Struct) -> Struct {
+    pub fn ensure_struct_le(st: Struct) -> Struct {
         st.swap_bytes::<endian::Little>()
     }
 
     #[inline(never)]
-    pub fn ensure_struct_big(st: Struct) -> Struct {
+    pub fn ensure_struct_be(st: Struct) -> Struct {
         st.swap_bytes::<endian::Big>()
     }
 
@@ -167,17 +169,29 @@ pub mod musli_zerocopy_swap {
     }
 
     #[inline(never)]
-    pub fn ensure_enum_native(st: Enum) -> Enum {
+    pub fn ensure_enum_ne(st: Enum) -> Enum {
         st.swap_bytes::<endian::Native>()
     }
 
     #[inline(never)]
-    pub fn ensure_enum_little(st: Enum) -> Enum {
+    pub fn ensure_enum_le(st: Enum) -> Enum {
         st.swap_bytes::<endian::Little>()
     }
 
     #[inline(never)]
-    pub fn ensure_enum_big(st: Enum) -> Enum {
+    pub fn ensure_enum_be(st: Enum) -> Enum {
         st.swap_bytes::<endian::Big>()
     }
 }
+
+pub mod generic {
+    pub enum Enum {
+        Empty,
+        One(u32),
+        Two(u32, u64),
+    }
+
+    pub fn do_nothing(en: Enum) -> Enum {
+        en
+    }
+}

crates/musli-macros/src/zero_copy/mod.rs

@@ -158,8 +158,8 @@ fn expand(cx: &Ctxt, input: syn::DeriveInput) -> Result<TokenStream, ()> {
 
                     swap_bytes_block = quote! {
                         Self {
-                            #member: <#ty as #zero_copy>::swap_bytes::<#endianness>(self.#member),
-                            #(#ignored_members: self.#ignored_members,)*
+                            #member: <#ty as #zero_copy>::swap_bytes::<#endianness>(this.#member),
+                            #(#ignored_members: this.#ignored_members,)*
                         }
                     };
                 }
@@ -201,8 +201,8 @@ fn expand(cx: &Ctxt, input: syn::DeriveInput) -> Result<TokenStream, ()> {
 
                     swap_bytes_block = quote! {
                         Self {
-                            #(#members: <#types as #zero_copy>::swap_bytes::<#endianness>(self.#members),)*
-                            #(#ignored_members: self.#ignored_members,)*
+                            #(#members: <#types as #zero_copy>::swap_bytes::<#endianness>(this.#members),)*
+                            #(#ignored_members: this.#ignored_members,)*
                         }
                     };
                 }
@@ -397,7 +397,7 @@ fn expand(cx: &Ctxt, input: syn::DeriveInput) -> Result<TokenStream, ()> {
             };
 
             swap_bytes_block = quote! {
-                match self {
+                match this {
                     #(#load_variants),*
                 }
             };
@@ -454,7 +454,7 @@ fn expand(cx: &Ctxt, input: syn::DeriveInput) -> Result<TokenStream, ()> {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
     let (swap_bytes_block, can_swap_bytes) = if swap_bytes_self {
-        (quote!(self), quote!(true))
+        (quote!(this), quote!(true))
     } else {
         (swap_bytes_block, can_swap_bytes)
     };
@@ -487,7 +487,7 @@ fn expand(cx: &Ctxt, input: syn::DeriveInput) -> Result<TokenStream, ()> {
 
             #[inline]
             fn swap_bytes<#endianness: #byte_order>(self) -> Self {
-                #swap_bytes_block
+                <#endianness as #byte_order>::try_map(self, |this| #swap_bytes_block)
             }
         }
     })

crates/musli-zerocopy/src/endian/mod.rs

@@ -242,6 +242,11 @@ mod sealed {
 /// [`Little`], and its internals are intentionally hidden. Do not attempt
 /// to use them yourself.
 pub trait ByteOrder: 'static + Sized + self::sealed::Sealed {
+    /// Maps the `value` through `map`, unless the current byte order is
+    /// [`Native`].
+    #[doc(hidden)]
+    fn try_map<T, F>(value: T, map: F) -> T where F: FnOnce(T) -> T;
+
     /// Swap the bytes for a `usize` with the current byte order.
     #[doc(hidden)]
     fn swap_usize(value: usize) -> usize;
@@ -292,6 +297,18 @@ pub trait ByteOrder: 'static + Sized + self::sealed::Sealed {
 }
 
 impl ByteOrder for Little {
+    #[cfg(target_endian = "little")]
+    #[inline(always)]
+    fn try_map<T, F>(value: T, _: F) -> T where F: FnOnce(T) -> T {
+        value
+    }
+
+    #[cfg(not(target_endian = "little"))]
+    #[inline(always