prost_derive/field/
oneof.rs

1use anyhow::{bail, Error};
2use proc_macro2::TokenStream;
3use quote::quote;
4use syn::{parse_str, Lit, Meta, MetaNameValue, NestedMeta, 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                        lit: Lit::Str(ref lit),
25                        ..
26                    }) => parse_str::<Path>(&lit.value())?,
27                    Meta::List(ref list) if list.nested.len() == 1 => {
28                        // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
29                        if let NestedMeta::Meta(Meta::Path(ref path)) = list.nested[0] {
30                            if let Some(ident) = path.get_ident() {
31                                Path::from(ident.clone())
32                            } else {
33                                bail!("invalid oneof attribute: item must be an identifier");
34                            }
35                        } else {
36                            bail!("invalid oneof attribute: item must be an identifier");
37                        }
38                    }
39                    _ => bail!("invalid oneof attribute: {:?}", attr),
40                };
41                set_option(&mut ty, t, "duplicate oneof attribute")?;
42            } else if let Some(t) = tags_attr(attr)? {
43                set_option(&mut tags, t, "duplicate tags attributes")?;
44            } else {
45                unknown_attrs.push(attr);
46            }
47        }
48
49        let ty = match ty {
50            Some(ty) => ty,
51            None => return Ok(None),
52        };
53
54        match unknown_attrs.len() {
55            0 => (),
56            1 => bail!(
57                "unknown attribute for message field: {:?}",
58                unknown_attrs[0]
59            ),
60            _ => bail!("unknown attributes for message field: {:?}", unknown_attrs),
61        }
62
63        let tags = match tags {
64            Some(tags) => tags,
65            None => bail!("oneof field is missing a tags attribute"),
66        };
67
68        Ok(Some(Field { ty, tags }))
69    }
70
71    /// Returns a statement which encodes the oneof field.
72    pub fn encode(&self, ident: TokenStream) -> TokenStream {
73        quote! {
74            if let Some(ref oneof) = #ident {
75                oneof.encode(buf)
76            }
77        }
78    }
79
80    /// Returns an expression which evaluates to the result of decoding the oneof field.
81    pub fn merge(&self, ident: TokenStream) -> TokenStream {
82        let ty = &self.ty;
83        quote! {
84            #ty::merge(#ident, tag, wire_type, buf, ctx)
85        }
86    }
87
88    /// Returns an expression which evaluates to the encoded length of the oneof field.
89    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
90        let ty = &self.ty;
91        quote! {
92            #ident.as_ref().map_or(0, #ty::encoded_len)
93        }
94    }
95
96    pub fn clear(&self, ident: TokenStream) -> TokenStream {
97        quote!(#ident = ::core::option::Option::None)
98    }
99}
prost_derive/field/oneof.rs

prost_derive/field/
oneof.rs
