prost_derive/field/
oneof.rs

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1use anyhow::{bail, Error};
2use proc_macro2::TokenStream;
3use quote::quote;
4use syn::{parse_str, Expr, ExprLit, Ident, Lit, Meta, MetaNameValue, Path};
5
6use crate::field::{set_option, tags_attr};
7
8#[derive(Clone)]
9pub struct Field {
10    pub ty: Path,
11    pub tags: Vec<u32>,
12}
13
14impl Field {
15    pub fn new(attrs: &[Meta]) -> Result<Option<Field>, Error> {
16        let mut ty = None;
17        let mut tags = None;
18        let mut unknown_attrs = Vec::new();
19
20        for attr in attrs {
21            if attr.path().is_ident("oneof") {
22                let t = match *attr {
23                    Meta::NameValue(MetaNameValue {
24                        value:
25                            Expr::Lit(ExprLit {
26                                lit: Lit::Str(ref lit),
27                                ..
28                            }),
29                        ..
30                    }) => parse_str::<Path>(&lit.value())?,
31                    Meta::List(ref list) => list.parse_args::<Ident>()?.into(),
32                    _ => bail!("invalid oneof attribute: {:?}", attr),
33                };
34                set_option(&mut ty, t, "duplicate oneof attribute")?;
35            } else if let Some(t) = tags_attr(attr)? {
36                set_option(&mut tags, t, "duplicate tags attributes")?;
37            } else {
38                unknown_attrs.push(attr);
39            }
40        }
41
42        let ty = match ty {
43            Some(ty) => ty,
44            None => return Ok(None),
45        };
46
47        if !unknown_attrs.is_empty() {
48            bail!(
49                "unknown attribute(s) for message field: #[prost({})]",
50                quote!(#(#unknown_attrs),*)
51            );
52        }
53
54        let tags = match tags {
55            Some(tags) => tags,
56            None => bail!("oneof field is missing a tags attribute"),
57        };
58
59        Ok(Some(Field { ty, tags }))
60    }
61
62    /// Returns a statement which encodes the oneof field.
63    pub fn encode(&self, ident: TokenStream) -> TokenStream {
64        quote! {
65            if let Some(ref oneof) = #ident {
66                oneof.encode(buf)
67            }
68        }
69    }
70
71    /// Returns an expression which evaluates to the result of decoding the oneof field.
72    pub fn merge(&self, ident: TokenStream) -> TokenStream {
73        let ty = &self.ty;
74        quote! {
75            #ty::merge(#ident, tag, wire_type, buf, ctx)
76        }
77    }
78
79    /// Returns an expression which evaluates to the encoded length of the oneof field.
80    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
81        let ty = &self.ty;
82        quote! {
83            #ident.as_ref().map_or(0, #ty::encoded_len)
84        }
85    }
86
87    pub fn clear(&self, ident: TokenStream) -> TokenStream {
88        quote!(#ident = ::core::option::Option::None)
89    }
90}
prost_derive/field/oneof.rs

prost_derive/field/
oneof.rs
