lyra-engine/lyra-reflect/lyra-reflect-derive/src/lib.rs

use proc_macro::TokenStream;
use proc_macro2::Ident;
use quote::{quote, ToTokens};
use syn::{Generics, Path, Attribute, GenericParam, parse_macro_input, DeriveInput, TypeParamBound};

mod enum_derive;
#[allow(unused_imports)]
use enum_derive::*;

mod struct_derive;
#[allow(unused_imports)]
use struct_derive::*;

mod struct_macro;

/* #[proc_macro_attribute(attributes(reflect))]
pub fn reflect(_attr: proc_macro::TokenStream, item: proc_macro::TokenStream) -> proc_macro::TokenStream {
    item
} */

pub(crate) struct FieldAttributes(Vec<ReflectAttribute>);

impl FieldAttributes {
    /// Searches for a usage of the 'reflect' attribute and returns a list of the
    /// things used in the usage.
    pub fn from_vec(v: &Vec<syn::Attribute>) -> Result<Self, syn::Error> {
        let s: Result<Vec<ReflectAttribute>, _> = v.iter().filter_map(|att| match &att.meta {
            syn::Meta::Path(_) => None,
            syn::Meta::List(l) => {
                Some(syn::parse::<ReflectAttribute>(l.tokens.clone().into()))
            }
            syn::Meta::NameValue(_) => None
        }).collect();

        Ok(Self(s?))
    }

    pub fn has_skip(&self) -> bool {
        self.0.iter().any(|a| *a == ReflectAttribute::Skip)
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub(crate) enum ReflectAttribute {
    Skip
}

impl syn::parse::Parse for ReflectAttribute {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let ident: Ident = input.parse()?;
        let ident_str = ident.to_string().to_lowercase();

        match ident_str.as_str() {
            "skip" => Ok(Self::Skip),
            _ => Err(syn::Error::new(ident.span(), "Unknown reflect attribute flag"))
        }
    }
}

#[allow(dead_code)]
pub(crate) struct ReflectDef {
    //pub ident: Ident,
    pub type_path: Path,
    pub generics: Generics,
    pub attributes: Vec<Attribute>
}

impl syn::parse::Parse for ReflectDef {
    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
        let attributes = input.call(Attribute::parse_outer)?;
        let type_path = Path::parse_mod_style(input)?;
        //let ident = type_path. //type_path.require_ident()?;
        let mut generics = input.parse::<Generics>()?;
        generics.where_clause = input.parse()?;

        Ok(Self {
            //ident: ident.clone(),
            type_path,
            generics,
            attributes,
        })
    }
}

#[proc_macro_derive(Reflect, attributes(reflect))]
pub fn derive_reflect(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    let stream = match &input.data {
        syn::Data::Enum(e) => {
            enum_derive::derive_reflect_enum(&input, e)
        },
        syn::Data::Struct(s) => {
            struct_derive::derive_reflect_struct(&input, s)
        },
        //syn::Data::Union(_) => todo!(),
        _ => todo!()
    };

    proc_macro::TokenStream::from(stream)
}

/// Implements `Reflect` for Values. `ReflectRef` and `ReflectMut` will be the `Value`
/// variants, its used for simple types and primitives.
#[proc_macro]
pub fn impl_reflect_trait_value(input: TokenStream) -> TokenStream {
    let reflect = syn::parse_macro_input!(input as ReflectDef);

    let type_path = reflect.type_path;
    // convert the type path to a string. This would not create a leading separator
    let type_path_str = {
        let idents: Vec<String> = type_path.segments.iter()
            .map(|segment| segment.ident.to_string())
            .collect();
        idents.join("::")
    };

    let (impl_generics, ty_generics, where_clause) = reflect.generics.split_for_impl();

    TokenStream::from(quote! {
        impl #impl_generics lyra_engine::reflect::Reflect for #type_path #ty_generics #where_clause {
            fn name(&self) -> ::std::string::String {
                #type_path_str.to_string()
            }
        
            fn type_id(&self) -> std::any::TypeId {
                std::any::TypeId::of::<#type_path #ty_generics>()
            }
        
            fn as_any(&self) -> &dyn std::any::Any {
                self
            }
        
            fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
                self
            }
        
            fn apply(&mut self, val: &dyn lyra_engine::reflect::Reflect) {
                let val = val.as_any().downcast_ref::<Self>()
                    .expect("The type of `val` is not the same as `self`");
                *self = val.clone();
            }

            fn clone_inner(&self) -> Box<dyn lyra_engine::reflect::Reflect> {
                Box::new(self.clone())
            }

            fn reflect_ref(&self) -> lyra_engine::reflect::ReflectRef {
                lyra_engine::reflect::ReflectRef::Value(self)
            }

            fn reflect_mut(&mut self) -> lyra_engine::reflect::ReflectMut {
                lyra_engine::reflect::ReflectMut::Value(self)
            }

            fn reflect_val(&self) -> &dyn lyra_engine::reflect::Reflect {
                self
            }

            fn reflect_val_mut(&mut self) -> &mut dyn lyra_engine::reflect::Reflect {
                self
            }
        }
    })
}

pub(crate) fn add_trait_bounds(mut generics: Generics, add_bounds: Vec<TypeParamBound>) -> Generics {
    for param in &mut generics.params {
        if let GenericParam::Type(ref mut type_param) = *param {
            for bound in add_bounds.iter() {
                type_param.bounds.push(bound.clone());
            }
        }
    }
    generics
}

#[proc_macro]
pub fn impl_reflect_simple_struct(input: TokenStream) -> TokenStream {
    struct_macro::impl_reflect_simple_struct(input)
}