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use syn::{spanned::Spanned, Data, DeriveInput};
use super::{is_ignore, is_unknown, is_with, EnumType};
pub fn expand(DeriveInput { ident, data, .. }: DeriveInput) -> syn::ItemImpl {
match data {
Data::Struct(data) => {
let is_named = data.fields.iter().any(|field| field.ident.is_some());
let names = data
.fields
.iter()
.enumerate()
.map(|(idx, field)| match field.ident.as_ref() {
Some(name) => name.clone(),
None => {
let name = format!("unit{idx}");
syn::Ident::new(&name, field.span())
}
})
.collect::<Vec<_>>();
let fields = data.fields.iter()
.zip(names.iter())
.map(|(field, field_name)| -> syn::Stmt {
let ty = &field.ty;
let value: syn::Expr = match (is_with(&field.attrs), is_ignore(&field.attrs)) {
(Some(with_type), false) => syn::parse_quote!(<#with_type<#ty> as cbor4ii::core::dec::Decode<'_>>::decode(reader)?.0),
(None, false) => syn::parse_quote!(<#ty as cbor4ii::core::dec::Decode<'_>>::decode(reader)?),
(None, true) => syn::parse_quote!(<#ty as Default>::default()),
(Some(_), true) => panic!("Cannot use both #[encoding(with)] and #[encoding(ignore)] attributes on the same field")
};
syn::parse_quote!{
let #field_name = #value;
}
});
let build_struct: syn::Expr = if is_named {
syn::parse_quote! { #ident { #(#names),* } }
} else {
syn::parse_quote! { #ident ( #(#names),* ) }
};
let count = data.fields.len();
let head: Option<syn::Stmt> = (count != 1).then(|| {
syn::parse_quote! {
let len = <cbor4ii::core::types::Array<()>>::len(reader)?.unwrap();
}
});
let tail: Option<syn::Stmt> = head.is_some().then(|| {
syn::parse_quote! {
// ignore unknown field
for _ in 0..(len - #count) {
cbor4ii::core::dec::IgnoredAny::decode(reader)?;
}
}
});
syn::parse_quote! {
impl<'de> cbor4ii::core::dec::Decode<'de> for #ident {
#[inline]
fn decode<R: cbor4ii::core::dec::Read<'de>>(reader: &mut R)
-> Result<Self, cbor4ii::core::error::DecodeError<R::Error>>
{
#head;
let value = {
#(#fields)*
#build_struct
};
#tail
Ok(value)
}
}
}
}
Data::Enum(data) => {
let enum_type = data.variants.iter().filter(|v| !is_unknown(&v.attrs)).fold(
None,
|mut sum, next| {
let ty = match &next.fields {
syn::Fields::Named(_) => EnumType::Struct,
syn::Fields::Unnamed(fields) if fields.unnamed.len() == 1 => EnumType::One,
syn::Fields::Unit => EnumType::Unit,
syn::Fields::Unnamed(_) => {
panic!("more than 1 unnamed member field are not allowed")
}
};
match (*sum.get_or_insert(ty), ty) {
(EnumType::Struct, EnumType::Struct)
| (EnumType::Struct, EnumType::Unit)
| (EnumType::Unit, EnumType::Unit)
| (EnumType::One, EnumType::One) => (),
(EnumType::Unit, EnumType::One)
| (EnumType::One, EnumType::Unit)
| (_, EnumType::Struct) => sum = Some(EnumType::Struct),
_ => panic!("enum member types must be consistent: {:?}", (sum, ty)),
}
sum
},
);
let enum_type = enum_type.expect("enum cannot be empty");
let mut iter = data.variants.iter().peekable();
let unknown_arm: Option<syn::Arm> = iter.next_if(|variant| is_unknown(&variant.attrs))
.map(|unknown| {
let name = &unknown.ident;
assert!(
unknown.discriminant.is_none(),
"unknown member is not allowed custom discriminant"
);
assert!(
is_with(&unknown.attrs).is_none(),
"unknown member is not allowed with type"
);
match &unknown.fields {
syn::Fields::Unnamed(fields) => match fields.unnamed.len() {
1 => {
assert_eq!(enum_type, EnumType::Unit);
syn::parse_quote! {
tag => #ident::#name(tag),
}
}
2 => {
assert_eq!(enum_type, EnumType::One);
let val_ty = &fields.unnamed[1].ty;
syn::parse_quote! {
tag => {
let tag: u32 = tag.try_into().map_err(|_| cbor4ii::core::error::DecodeError::CastOverflow {
name: &"unknown-tag",
})?;
let val = <#val_ty as cbor4ii::core::dec::Decode<'_>>::decode(reader)?;
#ident::#name(tag, val)
},
}
}
_ => panic!("unknown member must be a tag and a value"),
},
_ => panic!("named enum unsupported"),
}
});
if matches!(enum_type, EnumType::Struct) {
assert!(
unknown_arm.is_none(),
"struct enum does not allow unknown variants"
);
}
let mut discriminant: u32 = 0;
let fields = iter
.map(|field| -> syn::Arm {
match field.discriminant.as_ref() {
Some((_, syn::Expr::Lit(syn::ExprLit { lit: syn::Lit::Int(lit), .. }))) => {
discriminant = lit.base10_parse::<u32>().unwrap();
},
Some(_) => panic!("unsupported discriminant type"),
None => (),
};
discriminant += 1;
let idx = discriminant as u64;
let name = &field.ident;
assert!(!is_unknown(&field.attrs), "unknown member must be first");
match enum_type {
EnumType::Unit => {
assert!(is_with(&field.attrs).is_none(), "unit member is not allowed with type");
syn::parse_quote!{
#idx => #ident::#name,
}
},
EnumType::One => {
let val_ty = &field.fields.iter().next().unwrap().ty;
let value: syn::Expr = match is_with(&field.attrs) {
Some(with_type)
=> syn::parse_quote!(<#with_type<#val_ty> as cbor4ii::core::dec::Decode<'_>>::decode(reader)?.0),
None => syn::parse_quote!(<#val_ty as cbor4ii::core::dec::Decode<'_>>::decode(reader)?)
};
syn::parse_quote!{
#idx => #ident::#name(#value),
}
},
EnumType::Struct => {
let is_named = field.fields.iter().all(|field| field.ident.is_some());
let names = field.fields.iter()
.enumerate()
.map(|(idx, field)| match field.ident.as_ref() {
Some(name) => name.clone(),
None => {
let name = format!("unit{idx}");
syn::Ident::new(&name, field.span())
}
})
.collect::<Vec<_>>();
let count = field.fields.len();
let stmt = field.fields.iter()
.zip(names.iter())
.map(|(field, field_name)| -> syn::Stmt {
let val_ty = &field.ty;
match is_with(&field.attrs) {
Some(with_type) => syn::parse_quote!{
let #field_name = <#with_type<#val_ty> as cbor4ii::core::dec::Decode<'_>>::decode(reader)?.0;
},
None => syn::parse_quote!{
let #field_name = <#val_ty as cbor4ii::core::dec::Decode<'_>>::decode(reader)?;
}
}
});
let build_struct: syn::Expr = if is_named {
syn::parse_quote! { #ident::#name { #(#names),* } }
} else {
syn::parse_quote! { #ident::#name ( #(#names),* ) }
};
syn::parse_quote!{
#idx => {
let len = cbor4ii::core::types::Array::len(reader)?.unwrap();
let value = {
#(#stmt)*
#build_struct
};
// ignore unknown field
for _ in 0..(len - #count) {
cbor4ii::core::dec::IgnoredAny::decode(reader)?;
}
value
},
}
}
}
});
let unknown_arm = match unknown_arm {
Some(arm) => arm,
None => {
syn::parse_quote! {
tag => {
let err = cbor4ii::core::error::DecodeError::Custom {
name: &stringify!(#ident),
num: tag as u32
};
return Err(err);
}
}
}
};
let tag: syn::Stmt = if matches!(enum_type, EnumType::Unit) {
syn::parse_quote! {
let tag = <u64 as cbor4ii::core::dec::Decode<'_>>::decode(reader)?;
}
} else {
syn::parse_quote! {
let tag = <cbor4ii::core::types::Tag<()>>::tag(reader)?;
}
};
syn::parse_quote! {
impl<'de> cbor4ii::core::dec::Decode<'de> for #ident {
#[inline]
fn decode<R: cbor4ii::core::dec::Read<'de>>(reader: &mut R)
-> Result<Self, cbor4ii::core::error::DecodeError<R::Error>>
{
#tag
let value = match tag {
#(#fields)*
#unknown_arm
};
Ok(value)
}
}
}
}
Data::Union(_) => panic!("union unsupported"),
}
}