From 90d28fc314747039a710d2561a5ca2007d9378ad Mon Sep 17 00:00:00 2001
From: Tage Johansson <frans.tage@gmail.com>
Date: Fri, 21 Oct 2022 00:27:46 +0200
Subject: [PATCH 1/3] Serialize and deserialize a tagged newtype variant over
 unit () as if it was a unit variant.

---
 serde/src/private/de.rs              | 11 +++++++++++
 serde/src/private/ser.rs             |  6 +++---
 test_suite/tests/test_annotations.rs | 28 ++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index f0697d64f..6af958e39 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -1262,6 +1262,17 @@ mod content {
         {
             match self.content {
                 Content::Unit => visitor.visit_unit(),
+
+                // As a special case, allow deserializing newtype variant containing unit. E.G:
+                // #[derive(Deserialize)]
+                // #[serde(tag = "result")]
+                // enum Response<T> {
+                //     Success(T),
+                // }
+                //
+                // We want {"result": "Success"} to deserialize into `Response<T>`.
+                Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
+                Content::Seq(ref v) if v.is_empty() => visitor.visit_unit(),
                 _ => Err(self.invalid_type(&visitor)),
             }
         }
diff --git a/serde/src/private/ser.rs b/serde/src/private/ser.rs
index 6ee999389..293d8a865 100644
--- a/serde/src/private/ser.rs
+++ b/serde/src/private/ser.rs
@@ -51,7 +51,6 @@ enum Unsupported {
     String,
     ByteArray,
     Optional,
-    Unit,
     #[cfg(any(feature = "std", feature = "alloc"))]
     UnitStruct,
     Sequence,
@@ -70,7 +69,6 @@ impl Display for Unsupported {
             Unsupported::String => formatter.write_str("a string"),
             Unsupported::ByteArray => formatter.write_str("a byte array"),
             Unsupported::Optional => formatter.write_str("an optional"),
-            Unsupported::Unit => formatter.write_str("unit"),
             #[cfg(any(feature = "std", feature = "alloc"))]
             Unsupported::UnitStruct => formatter.write_str("unit struct"),
             Unsupported::Sequence => formatter.write_str("a sequence"),
@@ -184,7 +182,9 @@ where
     }
 
     fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
-        Err(self.bad_type(Unsupported::Unit))
+        let mut map = try!(self.delegate.serialize_map(Some(1)));
+        try!(map.serialize_entry(self.tag, self.variant_name));
+        map.end()
     }
 
     fn serialize_unit_struct(self, _: &'static str) -> Result<Self::Ok, Self::Error> {
diff --git a/test_suite/tests/test_annotations.rs b/test_suite/tests/test_annotations.rs
index 0317def6d..0ad25c88e 100644
--- a/test_suite/tests/test_annotations.rs
+++ b/test_suite/tests/test_annotations.rs
@@ -2302,6 +2302,34 @@ fn test_internally_tagged_enum_containing_flatten() {
     );
 }
 
+#[test]
+fn test_internally_tagged_enum_new_type_with_unit() {
+    #[derive(Serialize, Deserialize, PartialEq, Debug)]
+    #[serde(tag = "t")]
+    enum Data {
+        A(()),
+    }
+
+    assert_tokens(
+        &Data::A(()),
+        &[
+            Token::Map { len: Some(1) },
+            Token::Str("t"),
+            Token::Str("A"),
+            Token::MapEnd,
+        ],
+    );
+    assert_ser_tokens(
+        &Data::A(()),
+        &[
+            Token::Map { len: Some(1) },
+            Token::Str("t"),
+            Token::Str("A"),
+            Token::MapEnd,
+        ],
+    );
+}
+
 #[test]
 fn test_adjacently_tagged_enum_containing_flatten() {
     #[derive(Serialize, Deserialize, PartialEq, Debug)]

From a07d794f74475677544fdb35b981141ff8284c0b Mon Sep 17 00:00:00 2001
From: tage64 <40422978+tage64@users.noreply.github.com>
Date: Fri, 21 Oct 2022 08:53:55 +0200
Subject: [PATCH 2/3] Update test_suite/tests/test_annotations.rs

Co-authored-by: David Tolnay <dtolnay@gmail.com>
---
 test_suite/tests/test_annotations.rs | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/test_suite/tests/test_annotations.rs b/test_suite/tests/test_annotations.rs
index 0ad25c88e..9f9e2135d 100644
--- a/test_suite/tests/test_annotations.rs
+++ b/test_suite/tests/test_annotations.rs
@@ -2319,15 +2319,6 @@ fn test_internally_tagged_enum_new_type_with_unit() {
             Token::MapEnd,
         ],
     );
-    assert_ser_tokens(
-        &Data::A(()),
-        &[
-            Token::Map { len: Some(1) },
-            Token::Str("t"),
-            Token::Str("A"),
-            Token::MapEnd,
-        ],
-    );
 }
 
 #[test]

From e2ccfd9ea7f118a29e27037e1da79aa29a7c1be8 Mon Sep 17 00:00:00 2001
From: Tage Johansson <frans.tage@gmail.com>
Date: Fri, 21 Oct 2022 09:07:27 +0200
Subject: [PATCH 3/3] Remove bad deserialization from sequence to internally
 tagged newtype variant over .

---
 serde/src/private/de.rs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index 6af958e39..7cb540c14 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -1272,7 +1272,6 @@ mod content {
                 //
                 // We want {"result": "Success"} to deserialize into `Response<T>`.
                 Content::Map(ref v) if v.is_empty() => visitor.visit_unit(),
-                Content::Seq(ref v) if v.is_empty() => visitor.visit_unit(),
                 _ => Err(self.invalid_type(&visitor)),
             }
         }