From 6e2c385fa55d223e3d9dd22ff126f81b4903e05b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?A=CC=81rpa=CC=81d=20Goretity?= <h2co3@h2co3.org>
Date: Wed, 6 Nov 2019 17:31:27 +0100
Subject: [PATCH 1/4] Allow untagged unit variants to deserialize from
 `Visitor::visit_none()`

---
 serde/src/private/de.rs     | 7 +++++++
 test_suite/tests/test_de.rs | 9 +++++++++
 2 files changed, 16 insertions(+)

diff --git a/serde/src/private/de.rs b/serde/src/private/de.rs
index ffa5012dc..1c7fda3a1 100644
--- a/serde/src/private/de.rs
+++ b/serde/src/private/de.rs
@@ -2510,6 +2510,13 @@ mod content {
         {
             Ok(())
         }
+
+        fn visit_none<E>(self) -> Result<(), E>
+        where
+            E: de::Error,
+        {
+            Ok(())
+        }
     }
 }
 
diff --git a/test_suite/tests/test_de.rs b/test_suite/tests/test_de.rs
index 025d87b09..a1da9509c 100644
--- a/test_suite/tests/test_de.rs
+++ b/test_suite/tests/test_de.rs
@@ -137,6 +137,12 @@ enum EnumOther {
     Other,
 }
 
+#[derive(PartialEq, Debug, Deserialize)]
+#[serde(untagged)]
+enum EnumUntaggedUnit {
+    Unit,
+}
+
 #[derive(PartialEq, Debug)]
 struct IgnoredAny;
 
@@ -788,6 +794,9 @@ declare_tests! {
             Token::Unit,
         ],
     }
+    test_enum_untagged_unit_from_none {
+        UntaggedUnit::Unit => &[Token::None],
+    }
     test_box {
         Box::new(0i32) => &[Token::I32(0)],
     }

From c796daed7cacc90e398300f130f8c60421762bfc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?A=CC=81rpa=CC=81d=20Goretity?= <h2co3@h2co3.org>
Date: Thu, 7 Nov 2019 12:58:09 +0100
Subject: [PATCH 2/4] Fix test for untagged unit variant

---
 test_suite/tests/test_de.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test_suite/tests/test_de.rs b/test_suite/tests/test_de.rs
index a1da9509c..d9a0c8a40 100644
--- a/test_suite/tests/test_de.rs
+++ b/test_suite/tests/test_de.rs
@@ -795,7 +795,7 @@ declare_tests! {
         ],
     }
     test_enum_untagged_unit_from_none {
-        UntaggedUnit::Unit => &[Token::None],
+        EnumUntaggedUnit::Unit => &[Token::None],
     }
     test_box {
         Box::new(0i32) => &[Token::I32(0)],

From 59b99d2d60cca145bb82ad973de262405d5b77e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?A=CC=81rpa=CC=81d=20Goretity?= <h2co3@h2co3.org>
Date: Thu, 7 Nov 2019 21:18:12 +0100
Subject: [PATCH 3/4] Move test for untagged-variant-from-unit where it belongs

---
 test_suite/tests/test_de.rs     | 9 ---------
 test_suite/tests/test_macros.rs | 6 +-----
 2 files changed, 1 insertion(+), 14 deletions(-)

diff --git a/test_suite/tests/test_de.rs b/test_suite/tests/test_de.rs
index d9a0c8a40..025d87b09 100644
--- a/test_suite/tests/test_de.rs
+++ b/test_suite/tests/test_de.rs
@@ -137,12 +137,6 @@ enum EnumOther {
     Other,
 }
 
-#[derive(PartialEq, Debug, Deserialize)]
-#[serde(untagged)]
-enum EnumUntaggedUnit {
-    Unit,
-}
-
 #[derive(PartialEq, Debug)]
 struct IgnoredAny;
 
@@ -794,9 +788,6 @@ declare_tests! {
             Token::Unit,
         ],
     }
-    test_enum_untagged_unit_from_none {
-        EnumUntaggedUnit::Unit => &[Token::None],
-    }
     test_box {
         Box::new(0i32) => &[Token::I32(0)],
     }
diff --git a/test_suite/tests/test_macros.rs b/test_suite/tests/test_macros.rs
index c4eb06f36..d18b210ee 100644
--- a/test_suite/tests/test_macros.rs
+++ b/test_suite/tests/test_macros.rs
@@ -638,6 +638,7 @@ fn test_untagged_enum() {
     );
 
     assert_tokens(&Untagged::C, &[Token::Unit]);
+    assert_tokens(&Untagged::C, &[Token::None]);
 
     assert_tokens(&Untagged::D(4), &[Token::U8(4)]);
     assert_tokens(&Untagged::E("e".to_owned()), &[Token::Str("e")]);
@@ -652,11 +653,6 @@ fn test_untagged_enum() {
         ],
     );
 
-    assert_de_tokens_error::<Untagged>(
-        &[Token::None],
-        "data did not match any variant of untagged enum Untagged",
-    );
-
     assert_de_tokens_error::<Untagged>(
         &[Token::Tuple { len: 1 }, Token::U8(1), Token::TupleEnd],
         "data did not match any variant of untagged enum Untagged",

From 97a98a7031d051328f0d2841fdfe68d89029764f Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 24 Nov 2019 15:59:08 -0800
Subject: [PATCH 4/4] Test only deser for untagged unit visit_none

---
 test_suite/tests/test_macros.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/test_suite/tests/test_macros.rs b/test_suite/tests/test_macros.rs
index d18b210ee..d4456bed7 100644
--- a/test_suite/tests/test_macros.rs
+++ b/test_suite/tests/test_macros.rs
@@ -637,8 +637,10 @@ fn test_untagged_enum() {
         ],
     );
 
+    // Serializes to unit, deserializes from either depending on format's
+    // preference.
     assert_tokens(&Untagged::C, &[Token::Unit]);
-    assert_tokens(&Untagged::C, &[Token::None]);
+    assert_de_tokens(&Untagged::C, &[Token::None]);
 
     assert_tokens(&Untagged::D(4), &[Token::U8(4)]);
     assert_tokens(&Untagged::E("e".to_owned()), &[Token::Str("e")]);