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//! Deserialization for externally tagged enums:
//!
//! ```ignore
//! enum Enum {}
//! ```
use crate::de::enum_;
use crate::de::struct_;
use crate::de::tuple;
use crate::de::{
expr_is_missing, field_i, unwrap_to_variant_closure, wrap_deserialize_field_with,
wrap_deserialize_with, Parameters, StructForm, TupleForm,
};
use crate::fragment::{Expr, Fragment, Match};
use crate::internals::ast::{Field, Style, Variant};
use crate::internals::attr;
use crate::private;
use proc_macro2::TokenStream;
use quote::{quote, quote_spanned};
use syn::spanned::Spanned;
/// Generates `Deserialize::deserialize` body for an `enum Enum {...}` without additional attributes
pub(super) fn deserialize(
params: &Parameters,
variants: &[Variant],
cattrs: &attr::Container,
) -> Fragment {
let this_type = ¶ms.this_type;
let (de_impl_generics, de_ty_generics, ty_generics, where_clause) =
params.generics_with_de_lifetime();
let delife = params.borrowed.de_lifetime();
let type_name = cattrs.name().deserialize_name();
let expecting = format!("enum {}", params.type_name());
let expecting = cattrs.expecting().unwrap_or(&expecting);
let (variants_stmt, variant_visitor) = enum_::prepare_enum_variant_enum(variants);
// Match arms to extract a variant from a string
let variant_arms = variants
.iter()
.enumerate()
.filter(|&(_, variant)| !variant.attrs.skip_deserializing())
.map(|(i, variant)| {
let variant_name = field_i(i);
let block = Match(deserialize_externally_tagged_variant(
params, variant, cattrs,
));
quote! {
(__Field::#variant_name, __variant) => #block
}
});
let all_skipped = variants
.iter()
.all(|variant| variant.attrs.skip_deserializing());
let match_variant = if all_skipped {
// This is an empty enum like `enum Impossible {}` or an enum in which
// all variants have `#[serde(skip_deserializing)]`.
quote! {
// FIXME: Once feature(exhaustive_patterns) is stable:
// let _serde::#private::Err(__err) = _serde::de::EnumAccess::variant::<__Field>(__data);
// _serde::#private::Err(__err)
_serde::#private::Result::map(
_serde::de::EnumAccess::variant::<__Field>(__data),
|(__impossible, _)| match __impossible {})
}
} else {
quote! {
match _serde::de::EnumAccess::variant(__data)? {
#(#variant_arms)*
}
}
};
quote_block! {
#variant_visitor
#[doc(hidden)]
struct __Visitor #de_impl_generics #where_clause {
marker: _serde::#private::PhantomData<#this_type #ty_generics>,
lifetime: _serde::#private::PhantomData<&#delife ()>,
}
#[automatically_derived]
impl #de_impl_generics _serde::de::Visitor<#delife> for __Visitor #de_ty_generics #where_clause {
type Value = #this_type #ty_generics;
fn expecting(&self, __formatter: &mut _serde::#private::Formatter) -> _serde::#private::fmt::Result {
_serde::#private::Formatter::write_str(__formatter, #expecting)
}
fn visit_enum<__A>(self, __data: __A) -> _serde::#private::Result<Self::Value, __A::Error>
where
__A: _serde::de::EnumAccess<#delife>,
{
#match_variant
}
}
#variants_stmt
_serde::Deserializer::deserialize_enum(
__deserializer,
#type_name,
VARIANTS,
__Visitor {
marker: _serde::#private::PhantomData::<#this_type #ty_generics>,
lifetime: _serde::#private::PhantomData,
},
)
}
}
fn deserialize_externally_tagged_variant(
params: &Parameters,
variant: &Variant,
cattrs: &attr::Container,
) -> Fragment {
if let Some(path) = variant.attrs.deserialize_with() {
let (wrapper, wrapper_ty, unwrap_fn) = wrap_deserialize_variant_with(params, variant, path);
return quote_block! {
#wrapper
_serde::#private::Result::map(
_serde::de::VariantAccess::newtype_variant::<#wrapper_ty>(__variant), #unwrap_fn)
};
}
let variant_ident = &variant.ident;
match variant.style {
Style::Unit => {
let this_value = ¶ms.this_value;
quote_block! {
_serde::de::VariantAccess::unit_variant(__variant)?;
_serde::#private::Ok(#this_value::#variant_ident)
}
}
Style::Newtype => deserialize_externally_tagged_newtype_variant(
variant_ident,
params,
&variant.fields[0],
cattrs,
),
Style::Tuple => tuple::deserialize(
params,
&variant.fields,
cattrs,
TupleForm::ExternallyTagged(variant_ident),
),
Style::Struct => struct_::deserialize(
params,
&variant.fields,
cattrs,
StructForm::ExternallyTagged(variant_ident),
),
}
}
fn wrap_deserialize_variant_with(
params: &Parameters,
variant: &Variant,
deserialize_with: &syn::ExprPath,
) -> (TokenStream, TokenStream, TokenStream) {
let field_tys = variant.fields.iter().map(|field| field.ty);
let (wrapper, wrapper_ty) =
wrap_deserialize_with(params, "e!((#(#field_tys),*)), deserialize_with);
let unwrap_fn = unwrap_to_variant_closure(params, variant, true);
(wrapper, wrapper_ty, unwrap_fn)
}
fn deserialize_externally_tagged_newtype_variant(
variant_ident: &syn::Ident,
params: &Parameters,
field: &Field,
cattrs: &attr::Container,
) -> Fragment {
let this_value = ¶ms.this_value;
if field.attrs.skip_deserializing() {
let default = Expr(expr_is_missing(field, cattrs));
return quote_block! {
_serde::de::VariantAccess::unit_variant(__variant)?;
_serde::#private::Ok(#this_value::#variant_ident(#default))
};
}
match field.attrs.deserialize_with() {
None => {
let field_ty = field.ty;
let span = field.original.span();
let func =
quote_spanned!(span=> _serde::de::VariantAccess::newtype_variant::<#field_ty>);
quote_expr! {
_serde::#private::Result::map(#func(__variant), #this_value::#variant_ident)
}
}
Some(path) => {
let (wrapper, wrapper_ty) = wrap_deserialize_field_with(params, field.ty, path);
quote_block! {
#wrapper
_serde::#private::Result::map(
_serde::de::VariantAccess::newtype_variant::<#wrapper_ty>(__variant),
|__wrapper| #this_value::#variant_ident(__wrapper.value))
}
}
}
}