interoptopus_proc_impl 0.16.0

Macros to produce Interoptopus item info.
Documentation 
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use crate::runtime::args::FieldAttrs;
use syn::{DeriveInput, Field, Fields, Generics, Ident, Type};

pub struct RuntimeModel {
    pub name: Ident,
    pub generics: Generics,
    pub forward_field: ForwardField,
}

pub struct ForwardField {
    pub name: Ident,
    pub ty: Type,
}

impl RuntimeModel {
    pub fn from_derive_input(input: DeriveInput) -> syn::Result<Self> {
        let name = input.ident;
        let generics = input.generics;

        let fields = match input.data {
            syn::Data::Struct(data_struct) => match data_struct.fields {
                Fields::Named(fields) => fields.named.into_iter().collect::<Vec<_>>(),
                Fields::Unnamed(_) => return Err(syn::Error::new_spanned(name, "AsyncRuntime can only be derived for structs with named fields")),
                Fields::Unit => return Err(syn::Error::new_spanned(name, "AsyncRuntime can only be derived for structs with named fields")),
            },
            syn::Data::Enum(_) => return Err(syn::Error::new_spanned(name, "AsyncRuntime can only be derived for structs")),
            syn::Data::Union(_) => return Err(syn::Error::new_spanned(name, "AsyncRuntime can only be derived for structs")),
        };

        let forward_field = Self::find_forward_field(&fields)?;

        Ok(Self { name, generics, forward_field })
    }

    fn find_forward_field(fields: &[Field]) -> syn::Result<ForwardField> {
        // First, look for a field named "runtime"
        for field in fields {
            if let Some(field_name) = &field.ident
                && field_name == "runtime"
            {
                return Ok(ForwardField { name: field_name.clone(), ty: field.ty.clone() });
            }
        }

        // If no field named "runtime", look for field with #[runtime] attribute
        let mut runtime_attr_fields = Vec::new();
        for field in fields {
            let attrs = FieldAttrs::from_field(field);
            if attrs.has_runtime_attr {
                let name = field
                    .ident
                    .clone()
                    .ok_or_else(|| syn::Error::new_spanned(field, "Expected named field with #[runtime]"))?;
                runtime_attr_fields.push(ForwardField { name, ty: field.ty.clone() });
            }
        }

        match runtime_attr_fields.len() {
            0 => Err(syn::Error::new(proc_macro2::Span::call_site(), "AsyncRuntime requires either a field named 'runtime' or a field marked with #[runtime]")),
            1 => Ok(runtime_attr_fields.into_iter().next().unwrap()),
            _ => Err(syn::Error::new(proc_macro2::Span::call_site(), "AsyncRuntime found multiple fields marked with #[runtime], only one is allowed")),
        }
    }
}