From 38c130a30350401a0211e519bc7b06ae3df49ccd Mon Sep 17 00:00:00 2001
From: Mingun <alexander_sergey@mail.ru>
Date: Mon, 27 Feb 2023 21:08:30 +0500
Subject: [PATCH] Do not generate `DeserializeSeed` impl when not needed

This function is called for untagged, internally and externally tagged enums,
but `deserializer` parameter is `None` only for the latest. Only when it's `None`
`DeserializeSeed` impl is used
---
 serde_derive/src/de.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/serde_derive/src/de.rs b/serde_derive/src/de.rs
index f9d23926c..c0701625f 100644
--- a/serde_derive/src/de.rs
+++ b/serde_derive/src/de.rs
@@ -954,6 +954,7 @@ fn deserialize_struct(
             lifetime: _serde::__private::PhantomData,
         }
     };
+    let need_seed = deserializer.is_none();
     let dispatch = if let Some(deserializer) = deserializer {
         quote! {
             _serde::Deserializer::deserialize_any(#deserializer, #visitor_expr)
@@ -999,7 +1000,7 @@ fn deserialize_struct(
         _ => None,
     };
 
-    let visitor_seed = if is_enum && cattrs.has_flatten() {
+    let visitor_seed = if need_seed && is_enum && cattrs.has_flatten() {
         Some(quote! {
             impl #de_impl_generics _serde::de::DeserializeSeed<#delife> for __Visitor #de_ty_generics #where_clause {
                 type Value = #this_type #ty_generics;