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Remove code duplication when deriving Deserialize for adjacently tagged enums #2935

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Merged
merged 5 commits into from
Sep 20, 2025
+34 −27
Merged

Remove code duplication when deriving Deserialize for adjacently tagged enums #2935

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553a9ff
Document functions that are entry points for generating bodies of dif…
Mingun May 28, 2025
c451415
Do not duplicate variant deserialization code
Mingun May 28, 2025
2659b94
Create deserializer only when needed
Mingun May 28, 2025
6805bba
Inline variables that used only once
Mingun May 28, 2025
bfb020d
Use `variant` name for field instead of `field`
Mingun May 29, 2025
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61 changes: 34 additions & 27 deletions serde_derive/src/de.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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,
Expand Down Expand Up @@ -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(
Expand All @@ -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(
Expand All @@ -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;
Expand Down Expand Up @@ -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],
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -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],
Expand Down Expand Up @@ -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,
Expand Down Expand Up @@ -1209,6 +1217,7 @@ fn deserialize_struct_in_place(
})
}

/// Generates `Deserialize::deserialize` body for an `enum Enum {...}`
fn deserialize_enum(
params: &Parameters,
variants: &[Variant],
Expand Down Expand Up @@ -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],
Expand Down Expand Up @@ -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],
Expand Down Expand Up @@ -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],
Expand Down Expand Up @@ -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))
};
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -1589,10 +1593,13 @@ fn deserialize_adjacently_tagged_enum(
}
} else {
quote! {
let __ret = match #variant_from_map {
// Deserialize the buffered content now that we know the variant.
#(#variant_arms)*
}?;
let __seed = __Seed {
variant: #variant_from_map,
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
}
Expand All @@ -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 ()>,
}
Expand All @@ -1618,7 +1625,7 @@ fn deserialize_adjacently_tagged_enum(
where
__D: _serde::Deserializer<#delife>,
{
match self.field {
match self.variant {
#(#variant_arms)*
}
}
Expand Down Expand Up @@ -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,
})?;
Expand All @@ -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.
Expand All @@ -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,
},
Expand Down Expand Up @@ -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],
Expand Down
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