Fix error for invalid deku_id generation on generic enum

deku-derive/src/macros/deku_read.rs

@@ -409,8 +409,12 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
 
     // Implement `DekuEnumExt`
     if let Some(deku_id_type) = deku_id_type {
-        tokens.extend(quote! {
-            impl #imp DekuEnumExt<#lifetime, (#deku_id_type)> for #ident #wher {
+        if !imp.to_token_stream().is_empty() {
+            // Generics (#imp) are not supported, as our __deku
+            // would need to be appended to #imp
+        } else {
+            tokens.extend(quote! {
+            impl<'__deku> #imp ::#crate_::DekuEnumExt<#lifetime, (#deku_id_type)> for #ident #wher {
                 #[inline]
                 fn deku_id(&self) -> core::result::Result<(#deku_id_type), DekuError> {
                     match self {
@@ -420,6 +424,7 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
                 }
             }
         });
+        }
     }
 
     // println!("{}", tokens.to_string());

deku-derive/src/macros/mod.rs

@@ -4,6 +4,7 @@ use syn::parse::Parser;
 use syn::punctuated::Punctuated;
 use syn::spanned::Spanned;
 use syn::token::Comma;
+use syn::Lifetime;
 
 use crate::Num;
 
@@ -211,6 +212,10 @@ fn gen_type_from_ctx_id(
             if let syn::FnArg::Typed(pat_type) = arg {
                 if let syn::Pat::Ident(ident) = &*pat_type.pat {
                     if id == ident.ident {
+                        let mut pat_type = pat_type.clone();
+                        if let syn::Type::Reference(r) = pat_type.ty.as_mut() {
+                            r.lifetime = Some(Lifetime::new("'__deku", Span::call_site()));
+                        }
                         let ty = &pat_type.ty;
                         t = Some(quote! {#ty});
                     }

src/lib.rs

@@ -521,7 +521,7 @@ pub trait DekuUpdate {
 }
 
 /// "Extended Enum" trait: obtain additional enum information
-pub trait DekuEnumExt<'a, T> {
+pub trait DekuEnumExt<'__deku, T> {
     /// Obtain `id` of a given enum variant
     fn deku_id(&self) -> Result<T, DekuError>;
 }

tests/test_compile/cases/no_deku_id_generic_enum.rs

@@ -0,0 +1,13 @@
+use deku::prelude::*;
+
+#[derive(DekuRead)]
+#[deku(id_type = "u8")]
+pub enum Body<T: for<'a> DekuReader<'a>> {
+    #[deku(id = "0x0001")]
+    First(T),
+}
+
+fn main() {
+    let n = Body::<u8>::First(1);
+    n.deku_id();
+}

tests/test_compile/cases/no_deku_id_generic_enum.stderr

@@ -0,0 +1,12 @@
+error[E0599]: no method named `deku_id` found for enum `Body` in the current scope
+  --> tests/test_compile/cases/no_deku_id_generic_enum.rs:12:7
+   |
+5  | pub enum Body<T: for<'a> DekuReader<'a>> {
+   | ---------------------------------------- method `deku_id` not found for this enum
+...
+12 |     n.deku_id();
+   |       ^^^^^^^ method not found in `Body<u8>`
+   |
+   = help: items from traits can only be used if the trait is implemented and in scope
+   = note: the following trait defines an item `deku_id`, perhaps you need to implement it:
+           candidate #1: `deku::DekuEnumExt`