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use crate::utils::{DeriveType, HashMap};
use crate::utils::{SingleFieldData, State};
use proc_macro2::TokenStream;
use quote::quote;
use syn::{parse::Result, DeriveInput};
/// Provides the hook to expand `#[derive(FromStr)]` into an implementation of `FromStr`
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
let state = State::new(input, trait_name, trait_name.to_lowercase())?;
if state.derive_type == DeriveType::Enum {
Ok(enum_from(input, state, trait_name))
} else {
Ok(struct_from(&state, trait_name))
}
}
pub fn struct_from(state: &State, trait_name: &'static str) -> TokenStream {
// We cannot set defaults for fields, once we do we can remove this check
if state.fields.len() != 1 || state.enabled_fields().len() != 1 {
panic_one_field(trait_name);
}
let single_field_data = state.assert_single_enabled_field();
let SingleFieldData {
input_type,
field_type,
trait_path,
casted_trait,
impl_generics,
ty_generics,
where_clause,
..
} = single_field_data.clone();
let initializers = [quote! { #casted_trait::from_str(src)? }];
let body = single_field_data.initializer(&initializers);
quote! {
#[automatically_derived]
impl #impl_generics #trait_path for #input_type #ty_generics #where_clause {
type Err = <#field_type as #trait_path>::Err;
#[inline]
fn from_str(src: &str) -> ::core::result::Result<Self, Self::Err> {
Ok(#body)
}
}
}
}
fn enum_from(
input: &DeriveInput,
state: State,
trait_name: &'static str,
) -> TokenStream {
let mut variants_caseinsensitive = HashMap::default();
for variant_state in state.enabled_variant_data().variant_states {
let variant = variant_state.variant.unwrap();
if !variant.fields.is_empty() {
panic!("Only enums with no fields can derive({trait_name})")
}
variants_caseinsensitive
.entry(variant.ident.to_string().to_lowercase())
.or_insert_with(Vec::new)
.push(variant.ident.clone());
}
let input_type = &input.ident;
let input_type_name = input_type.to_string();
let mut cases = vec![];
// if a case insensitive match is unique match do that
// otherwise do a case sensitive match
for (ref canonical, ref variants) in variants_caseinsensitive {
if variants.len() == 1 {
let variant = &variants[0];
cases.push(quote! {
#canonical => #input_type::#variant,
})
} else {
for variant in variants {
let variant_str = variant.to_string();
cases.push(quote! {
#canonical if(src == #variant_str) => #input_type::#variant,
})
}
}
}
let trait_path = state.trait_path;
quote! {
impl #trait_path for #input_type {
type Err = ::derive_more::FromStrError;
#[inline]
fn from_str(src: &str) -> ::core::result::Result<Self, Self::Err> {
Ok(match src.to_lowercase().as_str() {
#(#cases)*
_ => return Err(::derive_more::FromStrError::new(#input_type_name)),
})
}
}
}
}
fn panic_one_field(trait_name: &str) -> ! {
panic!("Only structs with one field can derive({trait_name})")
}