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use anyhow::{bail, Error};
use proc_macro2::TokenStream;
use quote::quote;
use syn::{parse_str, Expr, ExprLit, Ident, Lit, Meta, MetaNameValue, Path};
use crate::field::{set_option, tags_attr};
#[derive(Clone)]
pub struct Field {
pub ty: Path,
pub tags: Vec<u32>,
}
impl Field {
pub fn new(attrs: &[Meta]) -> Result<Option<Field>, Error> {
let mut ty = None;
let mut tags = None;
let mut unknown_attrs = Vec::new();
for attr in attrs {
if attr.path().is_ident("oneof") {
let t = match *attr {
Meta::NameValue(MetaNameValue {
value:
Expr::Lit(ExprLit {
lit: Lit::Str(ref lit),
..
}),
..
}) => parse_str::<Path>(&lit.value())?,
Meta::List(ref list) => list.parse_args::<Ident>()?.into(),
_ => bail!("invalid oneof attribute: {:?}", attr),
};
set_option(&mut ty, t, "duplicate oneof attribute")?;
} else if let Some(t) = tags_attr(attr)? {
set_option(&mut tags, t, "duplicate tags attributes")?;
} else {
unknown_attrs.push(attr);
}
}
let ty = match ty {
Some(ty) => ty,
None => return Ok(None),
};
match unknown_attrs.len() {
0 => (),
1 => bail!(
"unknown attribute for message field: {:?}",
unknown_attrs[0]
),
_ => bail!("unknown attributes for message field: {:?}", unknown_attrs),
}
let tags = match tags {
Some(tags) => tags,
None => bail!("oneof field is missing a tags attribute"),
};
Ok(Some(Field { ty, tags }))
}
/// Returns a statement which encodes the oneof field.
pub fn encode(&self, ident: TokenStream) -> TokenStream {
quote! {
if let Some(ref oneof) = #ident {
oneof.encode(buf)
}
}
}
/// Returns an expression which evaluates to the result of decoding the oneof field.
pub fn merge(&self, ident: TokenStream) -> TokenStream {
let ty = &self.ty;
quote! {
#ty::merge(#ident, tag, wire_type, buf, ctx)
}
}
/// Returns an expression which evaluates to the encoded length of the oneof field.
pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
let ty = &self.ty;
quote! {
#ident.as_ref().map_or(0, #ty::encoded_len)
}
}
pub fn clear(&self, ident: TokenStream) -> TokenStream {
quote!(#ident = ::core::option::Option::None)
}
}