Release 1.0.226

Remove code duplication when deriving Deserialize for adjacently tagged enums

CONTRIBUTING.md

@@ -27,11 +27,11 @@ pull request with your changes. If anything does not pass, typically it will be
 easier to iterate and fix it locally than waiting for the CI servers to run
 tests for you.
 
-##### In the [`serde`] directory
+##### In the [`serde_core`] directory
 
 ```sh
 # Test all the example code in Serde documentation
-cargo test --features derive
+cargo test
 ```
 
 ##### In the [`test_suite`] directory
@@ -43,7 +43,7 @@ cargo +nightly test --features unstable
 
 Note that this test suite currently only supports running on a nightly compiler.
 
-[`serde`]: https://github.com/serde-rs/serde/tree/master/serde
+[`serde_core`]: https://github.com/serde-rs/serde/tree/master/serde_core
 [`test_suite`]: https://github.com/serde-rs/serde/tree/master/test_suite
 
 ## Conduct

serde/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "serde"
-version = "1.0.225"
+version = "1.0.226"
 authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
 build = "build.rs"
 categories = ["encoding", "no-std", "no-std::no-alloc"]
@@ -15,7 +15,7 @@ repository = "https://github.com/serde-rs/serde"
 rust-version = "1.56"
 
 [dependencies]
-serde_core = { version = "=1.0.225", path = "../serde_core", default-features = false, features = ["result"] }
+serde_core = { version = "=1.0.226", path = "../serde_core", default-features = false, features = ["result"] }
 serde_derive = { version = "1", optional = true, path = "../serde_derive" }
 
 [package.metadata.playground]
@@ -26,6 +26,7 @@ features = ["derive", "rc", "unstable"]
 targets = ["x86_64-unknown-linux-gnu"]
 rustdoc-args = [
     "--generate-link-to-definition",
+    "--generate-macro-expansion",
     "--extern-html-root-url=core=https://doc.rust-lang.org",
     "--extern-html-root-url=alloc=https://doc.rust-lang.org",
     "--extern-html-root-url=std=https://doc.rust-lang.org",

serde/src/lib.rs

@@ -95,7 +95,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 // Serde types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/serde/1.0.225")]
+#![doc(html_root_url = "https://docs.rs/serde/1.0.226")]
 // Support using Serde without the standard library!
 #![cfg_attr(not(feature = "std"), no_std)]
 // Show which crate feature enables conditionally compiled APIs in documentation.

serde_core/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "serde_core"
-version = "1.0.225"
+version = "1.0.226"
 authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
 build = "build.rs"
 categories = ["encoding", "no-std", "no-std::no-alloc"]
@@ -25,6 +25,7 @@ features = ["rc", "result", "unstable"]
 targets = ["x86_64-unknown-linux-gnu"]
 rustdoc-args = [
     "--generate-link-to-definition",
+    "--generate-macro-expansion",
     "--extern-html-root-url=core=https://doc.rust-lang.org",
     "--extern-html-root-url=alloc=https://doc.rust-lang.org",
     "--extern-html-root-url=std=https://doc.rust-lang.org",
@@ -36,7 +37,7 @@ rustdoc-args = [
 # is compatible with exactly one serde release because the generated code
 # involves nonpublic APIs which are not bound by semver.
 [target.'cfg(any())'.dependencies]
-serde_derive = { version = "=1.0.225", path = "../serde_derive" }
+serde_derive = { version = "=1.0.226", path = "../serde_derive" }
 
 
 ### FEATURES #################################################################

serde_core/src/lib.rs

@@ -35,7 +35,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 // Serde types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/serde_core/1.0.225")]
+#![doc(html_root_url = "https://docs.rs/serde_core/1.0.226")]
 // Support using Serde without the standard library!
 #![cfg_attr(not(feature = "std"), no_std)]
 // Show which crate feature enables conditionally compiled APIs in documentation.

serde_derive/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "serde_derive"
-version = "1.0.225"
+version = "1.0.226"
 authors = ["Erick Tryzelaar <erick.tryzelaar@gmail.com>", "David Tolnay <dtolnay@gmail.com>"]
 categories = ["no-std", "no-std::no-alloc"]
 description = "Macros 1.1 implementation of #[derive(Serialize, Deserialize)]"
@@ -34,6 +34,7 @@ serde = { version = "1", path = "../serde" }
 targets = ["x86_64-unknown-linux-gnu"]
 rustdoc-args = [
     "--generate-link-to-definition",
+    "--generate-macro-expansion",
     "--extern-html-root-url=core=https://doc.rust-lang.org",
     "--extern-html-root-url=alloc=https://doc.rust-lang.org",
     "--extern-html-root-url=std=https://doc.rust-lang.org",

serde_derive/src/de.rs

@@ -352,6 +352,7 @@ fn deserialize_in_place_body(_cont: &Container, _params: &Parameters) -> Option<
     None
 }
 
+/// Generates `Deserialize::deserialize` body for a type with `#[serde(transparent)]` attribute
 fn deserialize_transparent(cont: &Container, params: &Parameters) -> Fragment {
     let fields = match &cont.data {
         Data::Struct(_, fields) => fields,
@@ -394,6 +395,7 @@ fn deserialize_transparent(cont: &Container, params: &Parameters) -> Fragment {
     }
 }
 
+/// Generates `Deserialize::deserialize` body for a type with `#[serde(from)]` attribute
 fn deserialize_from(type_from: &syn::Type) -> Fragment {
     quote_block! {
         _serde::#private::Result::map(
@@ -402,6 +404,7 @@ fn deserialize_from(type_from: &syn::Type) -> Fragment {
     }
 }
 
+/// Generates `Deserialize::deserialize` body for a type with `#[serde(try_from)]` attribute
 fn deserialize_try_from(type_try_from: &syn::Type) -> Fragment {
     quote_block! {
         _serde::#private::Result::and_then(
@@ -410,6 +413,7 @@ fn deserialize_try_from(type_try_from: &syn::Type) -> Fragment {
     }
 }
 
+/// Generates `Deserialize::deserialize` body for a `struct Unit;`
 fn deserialize_unit_struct(params: &Parameters, cattrs: &attr::Container) -> Fragment {
     let this_type = &params.this_type;
     let this_value = &params.this_value;
@@ -465,6 +469,7 @@ enum TupleForm<'a> {
     Untagged(&'a syn::Ident, TokenStream),
 }
 
+/// Generates `Deserialize::deserialize` body for a `struct Tuple(...);` including `struct Newtype(T);`
 fn deserialize_tuple(
     params: &Parameters,
     fields: &[Field],
@@ -587,6 +592,7 @@ fn deserialize_tuple(
     }
 }
 
+/// Generates `Deserialize::deserialize_in_place` body for a `struct Tuple(...);` including `struct Newtype(T);`
 #[cfg(feature = "deserialize_in_place")]
 fn deserialize_tuple_in_place(
     params: &Parameters,
@@ -937,6 +943,7 @@ enum StructForm<'a> {
     Untagged(&'a syn::Ident, TokenStream),
 }
 
+/// Generates `Deserialize::deserialize` body for a `struct Struct {...}`
 fn deserialize_struct(
     params: &Parameters,
     fields: &[Field],
@@ -1119,6 +1126,7 @@ fn deserialize_struct(
     }
 }
 
+/// Generates `Deserialize::deserialize_in_place` body for a `struct Struct {...}`
 #[cfg(feature = "deserialize_in_place")]
 fn deserialize_struct_in_place(
     params: &Parameters,
@@ -1209,6 +1217,7 @@ fn deserialize_struct_in_place(
     })
 }
 
+/// Generates `Deserialize::deserialize` body for an `enum Enum {...}`
 fn deserialize_enum(
     params: &Parameters,
     variants: &[Variant],
@@ -1284,6 +1293,7 @@ fn prepare_enum_variant_enum(variants: &[Variant]) -> (TokenStream, Stmts) {
     (variants_stmt, variant_visitor)
 }
 
+/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` without additional attributes
 fn deserialize_externally_tagged_enum(
     params: &Parameters,
     variants: &[Variant],
@@ -1378,6 +1388,7 @@ fn deserialize_externally_tagged_enum(
     }
 }
 
+/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` with `#[serde(tag)]` attribute
 fn deserialize_internally_tagged_enum(
     params: &Parameters,
     variants: &[Variant],
@@ -1425,6 +1436,7 @@ fn deserialize_internally_tagged_enum(
     }
 }
 
+/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` with `#[serde(tag, content)]` attributes
 fn deserialize_adjacently_tagged_enum(
     params: &Parameters,
     variants: &[Variant],
@@ -1474,21 +1486,6 @@ fn deserialize_adjacently_tagged_enum(
         quote! { _serde::#private::de::TagContentOtherFieldVisitor }
     };
 
-    let tag_or_content = quote! {
-        #field_visitor_ty {
-            tag: #tag,
-            content: #content,
-        }
-    };
-
-    let variant_seed = quote! {
-        _serde::#private::de::AdjacentlyTaggedEnumVariantSeed::<__Field> {
-            enum_name: #rust_name,
-            variants: VARIANTS,
-            fields_enum: _serde::#private::PhantomData
-        }
-    };
-
     let mut missing_content = quote! {
         _serde::#private::Err(<__A::Error as _serde::de::Error>::missing_field(#content))
     };
@@ -1533,11 +1530,18 @@ fn deserialize_adjacently_tagged_enum(
 
     // Advance the map by one key, returning early in case of error.
     let next_key = quote! {
-        _serde::de::MapAccess::next_key_seed(&mut __map, #tag_or_content)?
+        _serde::de::MapAccess::next_key_seed(&mut __map, #field_visitor_ty {
+            tag: #tag,
+            content: #content,
+        })?
     };
 
     let variant_from_map = quote! {
-        _serde::de::MapAccess::next_value_seed(&mut __map, #variant_seed)?
+        _serde::de::MapAccess::next_value_seed(&mut __map, _serde::#private::de::AdjacentlyTaggedEnumVariantSeed::<__Field> {
+            enum_name: #rust_name,
+            variants: VARIANTS,
+            fields_enum: _serde::#private::PhantomData
+        })?
     };
 
     // When allowing unknown fields, we want to transparently step through keys
@@ -1589,10 +1593,13 @@ fn deserialize_adjacently_tagged_enum(
         }
     } else {
         quote! {
-            let __ret = match #variant_from_map {
+            let __seed = __Seed {
-                // Deserialize the buffered content now that we know the variant.
+                variant: #variant_from_map,
-                #(#variant_arms)*
+                marker: _serde::#private::PhantomData,
-            }?;
+                lifetime: _serde::#private::PhantomData,
+            };
+            let __deserializer = _serde::#private::de::ContentDeserializer::<__A::Error>::new(__content);
+            let __ret = _serde::de::DeserializeSeed::deserialize(__seed, __deserializer)?;
             // Visit remaining keys, looking for duplicates.
             #visit_remaining_keys
         }
@@ -1605,7 +1612,7 @@ fn deserialize_adjacently_tagged_enum(
 
         #[doc(hidden)]
         struct __Seed #de_impl_generics #where_clause {
-            field: __Field,
+            variant: __Field,
             marker: _serde::#private::PhantomData<#this_type #ty_generics>,
             lifetime: _serde::#private::PhantomData<&#delife ()>,
         }
@@ -1618,7 +1625,7 @@ fn deserialize_adjacently_tagged_enum(
             where
                 __D: _serde::Deserializer<#delife>,
             {
-                match self.field {
+                match self.variant {
                     #(#variant_arms)*
                 }
             }
@@ -1658,7 +1665,7 @@ fn deserialize_adjacently_tagged_enum(
                             _serde::#private::Some(_serde::#private::de::TagOrContentField::Content) => {
                                 let __ret = _serde::de::MapAccess::next_value_seed(&mut __map,
                                     __Seed {
-                                        field: __field,
+                                        variant: __field,
                                         marker: _serde::#private::PhantomData,
                                         lifetime: _serde::#private::PhantomData,
                                     })?;
@@ -1677,7 +1684,6 @@ fn deserialize_adjacently_tagged_enum(
                         match #next_relevant_key {
                             // Second key is the tag.
                             _serde::#private::Some(_serde::#private::de::TagOrContentField::Tag) => {
-                                let __deserializer = _serde::#private::de::ContentDeserializer::<__A::Error>::new(__content);
                                 #finish_content_then_tag
                             }
                             // Second key is a duplicate of the content.
@@ -1703,12 +1709,12 @@ fn deserialize_adjacently_tagged_enum(
             {
                 // Visit the first element - the tag.
                 match _serde::de::SeqAccess::next_element(&mut __seq)? {
-                    _serde::#private::Some(__field) => {
+                    _serde::#private::Some(__variant) => {
                         // Visit the second element - the content.
                         match _serde::de::SeqAccess::next_element_seed(
                             &mut __seq,
                             __Seed {
-                                field: __field,
+                                variant: __variant,
                                 marker: _serde::#private::PhantomData,
                                 lifetime: _serde::#private::PhantomData,
                             },
@@ -1742,6 +1748,7 @@ fn deserialize_adjacently_tagged_enum(
     }
 }
 
+/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` with `#[serde(untagged)]` attribute
 fn deserialize_untagged_enum(
     params: &Parameters,
     variants: &[Variant],

serde_derive/src/lib.rs

@@ -13,7 +13,7 @@
 //!
 //! [https://serde.rs/derive.html]: https://serde.rs/derive.html
 
-#![doc(html_root_url = "https://docs.rs/serde_derive/1.0.225")]
+#![doc(html_root_url = "https://docs.rs/serde_derive/1.0.226")]
 #![cfg_attr(not(check_cfg), allow(unexpected_cfgs))]
 // Ignored clippy lints
 #![allow(

serde_derive_internals/Cargo.toml

@@ -24,6 +24,7 @@ syn = { workspace = true, features = ["clone-impls", "derive", "parsing", "print
 targets = ["x86_64-unknown-linux-gnu"]
 rustdoc-args = [
     "--generate-link-to-definition",
+    "--generate-macro-expansion",
     "--extern-html-root-url=core=https://doc.rust-lang.org",
     "--extern-html-root-url=alloc=https://doc.rust-lang.org",
     "--extern-html-root-url=std=https://doc.rust-lang.org",

test_suite/tests/test_annotations.rs

@@ -2697,23 +2697,42 @@ mod flatten {
 
             #[test]
             fn newtype() {
+                let value = Flatten {
+                    data: Enum::Newtype(HashMap::from_iter([("key".into(), "value".into())])),
+                    extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
+                };
                 assert_tokens(
-                    &Flatten {
+                    &value,
-                        data: Enum::Newtype(HashMap::from_iter([("key".into(), "value".into())])),
-                        extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
-                    },
                     &[
                         Token::Map { len: None },
+                        // data
                         Token::Str("Newtype"), // variant
                         Token::Map { len: Some(1) },
                         Token::Str("key"),
                         Token::Str("value"),
                         Token::MapEnd,
+                        // extra
                         Token::Str("extra_key"),
                         Token::Str("extra value"),
                         Token::MapEnd,
                     ],
                 );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // extra
+                        Token::Str("extra_key"),
+                        Token::Str("extra value"),
+                        // data
+                        Token::Str("Newtype"), // variant
+                        Token::Map { len: Some(1) },
+                        Token::Str("key"),
+                        Token::Str("value"),
+                        Token::MapEnd,
+                        Token::MapEnd,
+                    ],
+                );
             }
 
             // Reaches crate::private::de::content::VariantDeserializer::tuple_variant
@@ -2721,23 +2740,42 @@ mod flatten {
             // via FlatMapDeserializer::deserialize_enum
             #[test]
             fn tuple() {
+                let value = Flatten {
+                    data: Enum::Tuple(0, 42),
+                    extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
+                };
                 assert_tokens(
-                    &Flatten {
+                    &value,
-                        data: Enum::Tuple(0, 42),
-                        extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
-                    },
                     &[
                         Token::Map { len: None },
+                        // data
                         Token::Str("Tuple"), // variant
                         Token::Seq { len: Some(2) },
                         Token::U32(0),
                         Token::U32(42),
                         Token::SeqEnd,
+                        // extra
                         Token::Str("extra_key"),
                         Token::Str("extra value"),
                         Token::MapEnd,
                     ],
                 );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // extra
+                        Token::Str("extra_key"),
+                        Token::Str("extra value"),
+                        // data
+                        Token::Str("Tuple"), // variant
+                        Token::Seq { len: Some(2) },
+                        Token::U32(0),
+                        Token::U32(42),
+                        Token::SeqEnd,
+                        Token::MapEnd,
+                    ],
+                );
             }
 
             // Reaches crate::private::de::content::VariantDeserializer::struct_variant
@@ -2745,26 +2783,45 @@ mod flatten {
             // via FlatMapDeserializer::deserialize_enum
             #[test]
             fn struct_from_seq() {
-                assert_de_tokens(
+                let value = Flatten {
-                    &Flatten {
+                    data: Enum::Struct {
-                        data: Enum::Struct {
+                        index: 0,
-                            index: 0,
+                        value: 42,
-                            value: 42,
-                        },
-                        extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
                     },
+                    extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
+                };
+                assert_de_tokens(
+                    &value,
                     &[
                         Token::Map { len: None },
+                        // data
                         Token::Str("Struct"), // variant
                         Token::Seq { len: Some(2) },
                         Token::U32(0),  // index
                         Token::U32(42), // value
                         Token::SeqEnd,
+                        // extra
                         Token::Str("extra_key"),
                         Token::Str("extra value"),
                         Token::MapEnd,
                     ],
                 );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // extra
+                        Token::Str("extra_key"),
+                        Token::Str("extra value"),
+                        // data
+                        Token::Str("Struct"), // variant
+                        Token::Seq { len: Some(2) },
+                        Token::U32(0),  // index
+                        Token::U32(42), // value
+                        Token::SeqEnd,
+                        Token::MapEnd,
+                    ],
+                );
             }
 
             // Reaches crate::private::de::content::VariantDeserializer::struct_variant
@@ -2772,16 +2829,18 @@ mod flatten {
             // via FlatMapDeserializer::deserialize_enum
             #[test]
             fn struct_from_map() {
-                assert_tokens(
+                let value = Flatten {
-                    &Flatten {
+                    data: Enum::Struct {
-                        data: Enum::Struct {
+                        index: 0,
-                            index: 0,
+                        value: 42,
-                            value: 42,
-                        },
-                        extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
                     },
+                    extra: HashMap::from_iter([("extra_key".into(), "extra value".into())]),
+                };
+                assert_tokens(
+                    &value,
                     &[
                         Token::Map { len: None },
+                        // data
                         Token::Str("Struct"), // variant
                         Token::Struct {
                             len: 2,
@@ -2792,11 +2851,33 @@ mod flatten {
                         Token::Str("value"),
                         Token::U32(42),
                         Token::StructEnd,
+                        // extra
                         Token::Str("extra_key"),
                         Token::Str("extra value"),
                         Token::MapEnd,
                     ],
                 );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // extra
+                        Token::Str("extra_key"),
+                        Token::Str("extra value"),
+                        // data
+                        Token::Str("Struct"), // variant
+                        Token::Struct {
+                            len: 2,
+                            name: "Struct",
+                        },
+                        Token::Str("index"),
+                        Token::U32(0),
+                        Token::Str("value"),
+                        Token::U32(42),
+                        Token::StructEnd,
+                        Token::MapEnd,
+                    ],
+                );
             }
         }
 
@@ -2817,6 +2898,7 @@ mod flatten {
             #[derive(Debug, PartialEq, Serialize, Deserialize)]
             #[serde(tag = "tag", content = "content")]
             enum Enum {
+                Unit,
                 Newtype(NewtypeVariant),
                 Struct { index: u32, value: u32 },
             }
@@ -2827,24 +2909,357 @@ mod flatten {
             }
 
             #[test]
-            fn struct_() {
+            fn unit() {
+                let value = Flatten {
+                    outer: 42,
+                    data: NewtypeWrapper(Enum::Unit),
+                };
+                // Field order: outer, [tag]
                 assert_tokens(
-                    &Flatten {
+                    &value,
-                        outer: 42,
-                        data: NewtypeWrapper(Enum::Struct {
-                            index: 0,
-                            value: 42,
-                        }),
-                    },
                     &[
                         Token::Map { len: None },
+                        // outer
                         Token::Str("outer"),
                         Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // content missing
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // content missing
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: outer, [tag, content]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: outer, [content, tag]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag, content], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content, tag], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag], outer, [content]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content], outer, [tag]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Unit,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Unit",
+                        },
+                        Token::MapEnd,
+                    ],
+                );
+            }
+
+            #[test]
+            fn newtype() {
+                let value = Flatten {
+                    outer: 42,
+                    data: NewtypeWrapper(Enum::Newtype(NewtypeVariant { value: 23 })),
+                };
+                // Field order: outer, [tag, content]
+                assert_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: outer, [content, tag]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag, content], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content, tag], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag], outer, [content]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content], outer, [tag]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 1,
+                            name: "NewtypeVariant",
+                        },
+                        Token::Str("value"),
+                        Token::U32(23),
+                        Token::StructEnd,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Newtype",
+                        },
+                        Token::MapEnd,
+                    ],
+                );
+            }
+
+            #[test]
+            fn struct_() {
+                let value = Flatten {
+                    outer: 42,
+                    data: NewtypeWrapper(Enum::Struct {
+                        index: 0,
+                        value: 42,
+                    }),
+                };
+                // Field order: outer, [tag, content]
+                assert_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
                         Token::Str("tag"),
                         Token::UnitVariant {
                             name: "Enum",
                             variant: "Struct",
                         },
+                        // content
                         Token::Str("content"),
                         Token::Struct {
                             len: 2,
@@ -2858,32 +3273,143 @@ mod flatten {
                         Token::MapEnd,
                     ],
                 );
-            }
+                // Field order: outer, [content, tag]
-
+                assert_de_tokens(
-            #[test]
+                    &value,
-            fn newtype() {
-                assert_tokens(
-                    &Flatten {
-                        outer: 42,
-                        data: NewtypeWrapper(Enum::Newtype(NewtypeVariant { value: 23 })),
-                    },
                     &[
                         Token::Map { len: None },
+                        // outer
                         Token::Str("outer"),
                         Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 2,
+                            name: "Struct",
+                        },
+                        Token::Str("index"),
+                        Token::U32(0),
+                        Token::Str("value"),
+                        Token::U32(42),
+                        Token::StructEnd,
+                        // tag
                         Token::Str("tag"),
                         Token::UnitVariant {
                             name: "Enum",
-                            variant: "Newtype",
+                            variant: "Struct",
                         },
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag, content], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Struct",
+                        },
+                        // content
                         Token::Str("content"),
                         Token::Struct {
-                            len: 1,
+                            len: 2,
-                            name: "NewtypeVariant",
+                            name: "Struct",
                         },
+                        Token::Str("index"),
+                        Token::U32(0),
                         Token::Str("value"),
-                        Token::U32(23),
+                        Token::U32(42),
                         Token::StructEnd,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content, tag], outer
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 2,
+                            name: "Struct",
+                        },
+                        Token::Str("index"),
+                        Token::U32(0),
+                        Token::Str("value"),
+                        Token::U32(42),
+                        Token::StructEnd,
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Struct",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [tag], outer, [content]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Struct",
+                        },
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 2,
+                            name: "Struct",
+                        },
+                        Token::Str("index"),
+                        Token::U32(0),
+                        Token::Str("value"),
+                        Token::U32(42),
+                        Token::StructEnd,
+                        Token::MapEnd,
+                    ],
+                );
+                // Field order: [content], outer, [tag]
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // content
+                        Token::Str("content"),
+                        Token::Struct {
+                            len: 2,
+                            name: "Struct",
+                        },
+                        Token::Str("index"),
+                        Token::U32(0),
+                        Token::Str("value"),
+                        Token::U32(42),
+                        Token::StructEnd,
+                        // outer
+                        Token::Str("outer"),
+                        Token::U32(42),
+                        // tag
+                        Token::Str("tag"),
+                        Token::UnitVariant {
+                            name: "Enum",
+                            variant: "Struct",
+                        },
                         Token::MapEnd,
                     ],
                 );
@@ -2917,17 +3443,20 @@ mod flatten {
                     D { d: i32 },
                 }
 
+                let value = Flatten {
+                    x: X::B { b: 1 },
+                    y: Y::D { d: 2 },
+                };
                 assert_tokens(
-                    &Flatten {
+                    &value,
-                        x: X::B { b: 1 },
-                        y: Y::D { d: 2 },
-                    },
                     &[
                         Token::Map { len: None },
+                        // x
                         Token::Str("typeX"),
                         Token::Str("B"),
                         Token::Str("b"),
                         Token::I32(1),
+                        // y
                         Token::Str("typeY"),
                         Token::Str("D"),
                         Token::Str("d"),
@@ -2935,11 +3464,28 @@ mod flatten {
                         Token::MapEnd,
                     ],
                 );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // y
+                        Token::Str("typeY"),
+                        Token::Str("D"),
+                        Token::Str("d"),
+                        Token::I32(2),
+                        // x
+                        Token::Str("typeX"),
+                        Token::Str("B"),
+                        Token::Str("b"),
+                        Token::I32(1),
+                        Token::MapEnd,
+                    ],
+                );
             }
 
             #[test]
             fn unit_enum_with_unknown_fields() {
-                #[derive(Debug, PartialEq, Deserialize)]
+                #[derive(Debug, PartialEq, Serialize, Deserialize)]
                 struct Flatten {
                     #[serde(flatten)]
                     x: X,
@@ -2947,31 +3493,49 @@ mod flatten {
                     y: Y,
                 }
 
-                #[derive(Debug, PartialEq, Deserialize)]
+                #[derive(Debug, PartialEq, Serialize, Deserialize)]
                 #[serde(tag = "typeX")]
                 enum X {
                     A,
                 }
 
-                #[derive(Debug, PartialEq, Deserialize)]
+                #[derive(Debug, PartialEq, Serialize, Deserialize)]
                 #[serde(tag = "typeY")]
                 enum Y {
                     B { c: u32 },
                 }
 
-                assert_de_tokens(
+                let value = Flatten {
-                    &Flatten {
+                    x: X::A,
-                        x: X::A,
+                    y: Y::B { c: 0 },
-                        y: Y::B { c: 0 },
+                };
-                    },
+                assert_tokens(
+                    &value,
                     &[
                         Token::Map { len: None },
+                        // x
                         Token::Str("typeX"),
                         Token::Str("A"),
+                        // y
                         Token::Str("typeY"),
                         Token::Str("B"),
                         Token::Str("c"),
-                        Token::I32(0),
+                        Token::U32(0),
+                        Token::MapEnd,
+                    ],
+                );
+                assert_de_tokens(
+                    &value,
+                    &[
+                        Token::Map { len: None },
+                        // y
+                        Token::Str("typeY"),
+                        Token::Str("B"),
+                        Token::Str("c"),
+                        Token::U32(0),
+                        // x
+                        Token::Str("typeX"),
+                        Token::Str("A"),
                         Token::MapEnd,
                     ],
                 );