Reduce generic copies of restore_position

Refs jam1garner#319.

Author: ScanMountGoat

binrw/src/binread/impls.rs

@@ -19,7 +19,7 @@ macro_rules! binread_impl {
                     let mut val = [0; core::mem::size_of::<$type_name>()];
                     let pos = reader.stream_position()?;
 
-                    reader.read_exact(&mut val).or_else(crate::__private::restore_position(reader, pos))?;
+                    reader.read_exact(&mut val).map_err(crate::__private::restore_position(reader, pos))?;
                     Ok(match endian {
                         Endian::Big => {
                             <$type_name>::from_be_bytes(val)

binrw/src/private.rs

@@ -167,13 +167,13 @@ where
     args
 }
 
-pub fn restore_position<E: Into<Error>, S: Seek, T>(
+pub fn restore_position<E: Into<Error>, S: Seek>(
     stream: &mut S,
     pos: u64,
-) -> impl FnOnce(E) -> BinResult<T> + '_ {
+) -> impl FnOnce(E) -> Error + '_ {
     move |error| match stream.seek(SeekFrom::Start(pos)) {
-        Ok(_) => Err(error.into()),
-        Err(seek_error) => Err(restore_position_err(error.into(), seek_error.into())),
+        Ok(_) => error.into(),
+        Err(seek_error) => restore_position_err(error.into(), seek_error.into()),
     }
 }
 

binrw_derive/src/binrw/codegen/read_options.rs

@@ -53,7 +53,7 @@ pub(crate) fn generate(input: &Input, derive_input: &syn::DeriveInput) -> TokenS
 
     let rewind = (needs_rewind || input.magic().is_some()).then(|| {
         quote! {
-            .or_else(#RESTORE_POSITION::<binrw::Error, _, _>(#reader_var, #POS))
+            .map_err(#RESTORE_POSITION::<binrw::Error, _>(#reader_var, #POS))
         }
     });