derive_more/
from_str.rs

1use crate::utils::{SingleFieldData, State};
2use proc_macro2::TokenStream;
3use quote::quote;
4use syn::{parse::Result, DeriveInput};
5
6/// Provides the hook to expand `#[derive(FromStr)]` into an implementation of `FromStr`
7pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
8    let state = State::new(
9        input,
10        trait_name,
11        quote!(::core::str),
12        trait_name.to_lowercase(),
13    )?;
14
15    // We cannot set defaults for fields, once we do we can remove this check
16    if state.fields.len() != 1 || state.enabled_fields().len() != 1 {
17        panic_one_field(trait_name);
18    }
19
20    let single_field_data = state.assert_single_enabled_field();
21    let SingleFieldData {
22        input_type,
23        field_type,
24        trait_path,
25        casted_trait,
26        impl_generics,
27        ty_generics,
28        where_clause,
29        ..
30    } = single_field_data.clone();
31
32    let initializers = [quote!(#casted_trait::from_str(src)?)];
33    let body = single_field_data.initializer(&initializers);
34
35    Ok(quote! {
36        impl#impl_generics #trait_path for #input_type#ty_generics #where_clause
37        {
38            type Err = <#field_type as #trait_path>::Err;
39            #[inline]
40            fn from_str(src: &str) -> ::core::result::Result<Self, Self::Err> {
41                Ok(#body)
42            }
43        }
44    })
45}
46
47fn panic_one_field(trait_name: &str) -> ! {
48    panic!("Only structs with one field can derive({})", trait_name)
49}
derive_more/from_str.rs

derive_more/
from_str.rs
