From 6699b0bc404663064189c3a34d7934475741b3e5 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 25 Jan 2021 13:25:53 -0800
Subject: [PATCH 1/2] Add regression test for issue 1969

---
 test_suite/tests/test_gen.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/test_suite/tests/test_gen.rs b/test_suite/tests/test_gen.rs
index 73f7fa50f..002885ead 100644
--- a/test_suite/tests/test_gen.rs
+++ b/test_suite/tests/test_gen.rs
@@ -7,6 +7,7 @@
 #![allow(
     unknown_lints,
     mixed_script_confusables,
+    clippy::ptr_arg,
     clippy::trivially_copy_pass_by_ref
 )]
 
@@ -735,6 +736,12 @@ fn test_gen() {
         #[serde(borrow = "'a")]
         f: mac!(Cow<'a, str>),
     }
+
+    #[derive(Serialize)]
+    struct Struct {
+        #[serde(serialize_with = "vec_first_element")]
+        vec: Vec<Self>,
+    }
 }
 
 //////////////////////////////////////////////////////////////////////////
@@ -808,3 +815,11 @@ where
 pub fn is_zero(n: &u8) -> bool {
     *n == 0
 }
+
+fn vec_first_element<T, S>(vec: &Vec<T>, serializer: S) -> StdResult<S::Ok, S::Error>
+where
+    T: Serialize,
+    S: Serializer,
+{
+    vec.first().serialize(serializer)
+}

From 2ba97394fb5e5c32b52ab8d82aed45b85fef0db7 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Mon, 25 Jan 2021 13:27:15 -0800
Subject: [PATCH 2/2] Substitute Self in output of Serialize derive

---
 serde_derive/src/lib.rs | 4 ++--
 serde_derive/src/ser.rs | 8 ++++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/serde_derive/src/lib.rs b/serde_derive/src/lib.rs
index f10baac01..8d1464ec8 100644
--- a/serde_derive/src/lib.rs
+++ b/serde_derive/src/lib.rs
@@ -79,8 +79,8 @@ mod try;
 
 #[proc_macro_derive(Serialize, attributes(serde))]
 pub fn derive_serialize(input: TokenStream) -> TokenStream {
-    let input = parse_macro_input!(input as DeriveInput);
-    ser::expand_derive_serialize(&input)
+    let mut input = parse_macro_input!(input as DeriveInput);
+    ser::expand_derive_serialize(&mut input)
         .unwrap_or_else(to_compile_errors)
         .into()
 }
diff --git a/serde_derive/src/ser.rs b/serde_derive/src/ser.rs
index 91154dc6a..c663c3b02 100644
--- a/serde_derive/src/ser.rs
+++ b/serde_derive/src/ser.rs
@@ -6,10 +6,14 @@ use bound;
 use dummy;
 use fragment::{Fragment, Match, Stmts};
 use internals::ast::{Container, Data, Field, Style, Variant};
-use internals::{attr, Ctxt, Derive};
+use internals::{attr, replace_receiver, Ctxt, Derive};
 use pretend;
 
-pub fn expand_derive_serialize(input: &syn::DeriveInput) -> Result<TokenStream, Vec<syn::Error>> {
+pub fn expand_derive_serialize(
+    input: &mut syn::DeriveInput,
+) -> Result<TokenStream, Vec<syn::Error>> {
+    replace_receiver(input);
+
     let ctxt = Ctxt::new();
     let cont = match Container::from_ast(&ctxt, input, Derive::Serialize) {
         Some(cont) => cont,