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Locate field that has the #[source] attribute

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This commit is contained in:
David Tolnay 2019-10-09 07:05:02 -07:00
parent f1dcfe0f0a
commit 4cdeec15e5
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GPG key ID: F9BA143B95FF6D82
3 changed files with 33 additions and 13 deletions
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12
impl/src/attr.rs Normal file
View file

@ -0,0 +1,12 @@
use syn::parse::Nothing;
use syn::{Field, Result};
pub fn is_source(field: &Field) -> Result<bool> {
for attr in &field.attrs {
if attr.path.is_ident("source") {
syn::parse2::<Nothing>(attr.tokens.clone())?;
return Ok(true);
}
}
Ok(false)
}

31
impl/src/expand.rs
View file

@ -1,8 +1,9 @@
use crate::attr;
use proc_macro2::TokenStream;
use quote::quote;
use syn::{
Data, DataEnum, DataStruct, DeriveInput, Error, Fields, FieldsNamed, FieldsUnnamed, Member,
Result,
Data, DataEnum, DataStruct, DeriveInput, Error, Fields, FieldsNamed, FieldsUnnamed, Index,
Member, Result,
};
pub fn derive(input: &DeriveInput) -> Result<TokenStream> {
@ -21,8 +22,8 @@ fn struct_error(input: &DeriveInput, data: &DataStruct) -> Result<TokenStream> {
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let source = match &data.fields {
Fields::Named(fields) => braced_struct_source(input, fields)?,
Fields::Unnamed(fields) => tuple_struct_source(input, fields)?,
Fields::Named(fields) => braced_struct_source(fields)?,
Fields::Unnamed(fields) => tuple_struct_source(fields)?,
Fields::Unit => None,
};
@ -41,16 +42,22 @@ fn struct_error(input: &DeriveInput, data: &DataStruct) -> Result<TokenStream> {
})
}
fn braced_struct_source(input: &DeriveInput, fields: &FieldsNamed) -> Result<Option<Member>> {
let _ = input;
let _ = fields;
unimplemented!()
fn braced_struct_source(fields: &FieldsNamed) -> Result<Option<Member>> {
for field in &fields.named {
if attr::is_source(field)? {
return Ok(Some(Member::Named(field.ident.as_ref().unwrap().clone())));
}
}
Ok(None)
}
fn tuple_struct_source(input: &DeriveInput, fields: &FieldsUnnamed) -> Result<Option<Member>> {
let _ = input;
let _ = fields;
unimplemented!()
fn tuple_struct_source(fields: &FieldsUnnamed) -> Result<Option<Member>> {
for (i, field) in fields.unnamed.iter().enumerate() {
if attr::is_source(field)? {
return Ok(Some(Member::Unnamed(Index::from(i))));
}
}
Ok(None)
}
fn enum_error(input: &DeriveInput, data: &DataEnum) -> Result<TokenStream> {

3
impl/src/lib.rs
View file

@ -1,11 +1,12 @@
extern crate proc_macro;
mod attr;
mod expand;
use proc_macro::TokenStream;
use syn::{parse_macro_input, DeriveInput};
#[proc_macro_derive(Error)]
#[proc_macro_derive(Error, attributes(source))]
pub fn derive_error(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
expand::derive(&input)