Potential fix for asserting bitsize on generic structs

bilge-impl/src/bitsize.rs

@@ -149,17 +149,21 @@ fn generate_struct(item: &ItemStruct, declared_bitsize: u8) -> TokenStream {
         }
     };
 
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
     quote! {
         #vis struct #ident #generics #fields_def
 
-        // constness: when we get const blocks evaluated at compile time, add a const computed_bitsize
-        const _: () = assert!(
-            (#computed_bitsize) == (#declared_bitsize),
-            concat!("struct size and declared bit size differ: ",
-            // stringify!(#computed_bitsize),
-            " != ",
-            stringify!(#declared_bitsize))
-        );
+        impl #impl_generics #ident #ty_generics #where_clause {
+            // constness: when we get const blocks evaluated at compile time, add a const computed_bitsize
+            const _bitsize_check: () = assert!(
+                (#computed_bitsize) == (#declared_bitsize),
+                concat!("struct size and declared bit size differ: ",
+                // stringify!(#computed_bitsize),
+                " != ",
+                stringify!(#declared_bitsize))
+            );
+        }
     }
 }
 

tests/struct.rs

@@ -510,11 +510,10 @@ impl_from!(T; Generic<T> => u2; |val| val.0);
 #[derive(DefaultBits, PartialEq, DebugBits, FromBits)]
 struct UsingGeneric(Generic<()>);
 
-// TODO: bitsize doesn't work here yet because of the size check: it's trying to get the size of Generic<T> in a non-generic context
-// #[bitsize(2)]
+#[bitsize(2)]
 // FromBits, DefaultBits, and DebugBits don't work yet because they need the generics threaded through to the correct spot.
-// #[derive(PartialEq)] // TODO: FromBits, DefaultBits, DebugBits
-// struct IsGeneric<T>(Generic<T>);
+#[derive(PartialEq)] // TODO: FromBits, DefaultBits, DebugBits
+struct IsGeneric<T>(Generic<T>);
 
 #[bitsize(2)]
 #[derive(DefaultBits, PartialEq, DebugBits, TryFromBits)]