prost_derive/field/
oneof.rs

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        match unknown_attrs.len() {
48            0 => (),
49            1 => bail!(
50                "unknown attribute for message field: {:?}",
51                unknown_attrs[0]
52            ),
53            _ => bail!("unknown attributes for message field: {:?}", unknown_attrs),
54        }
55
56        let tags = match tags {
57            Some(tags) => tags,
58            None => bail!("oneof field is missing a tags attribute"),
59        };
60
61        Ok(Some(Field { ty, tags }))
62    }
63
64    /// Returns a statement which encodes the oneof field.
65    pub fn encode(&self, ident: TokenStream) -> TokenStream {
66        quote! {
67            if let Some(ref oneof) = #ident {
68                oneof.encode(buf)
69            }
70        }
71    }
72
73    /// Returns an expression which evaluates to the result of decoding the oneof field.
74    pub fn merge(&self, ident: TokenStream) -> TokenStream {
75        let ty = &self.ty;
76        quote! {
77            #ty::merge(#ident, tag, wire_type, buf, ctx)
78        }
79    }
80
81    /// Returns an expression which evaluates to the encoded length of the oneof field.
82    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
83        let ty = &self.ty;
84        quote! {
85            #ident.as_ref().map_or(0, #ty::encoded_len)
86        }
87    }
88
89    pub fn clear(&self, ident: TokenStream) -> TokenStream {
90        quote!(#ident = ::core::option::Option::None)
91    }
92}
prost_derive/field/oneof.rs

prost_derive/field/
oneof.rs
