golem-rust-macro 3.0.0-rc2

// Copyright 2024-2026 Golem Cloud
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use proc_macro::TokenStream;
use quote::quote;
use syn::{Data, DeriveInput, Fields, parse_macro_input};

pub fn derive_multimodal(input: TokenStream) -> TokenStream {
    let input = parse_macro_input!(input as DeriveInput);
    let enum_name = &input.ident;

    let data_enum = match input.data {
        Data::Enum(data_enum) => data_enum,
        _ => {
            return syn::Error::new_spanned(input.ident, "Multimodal derive only supports enums")
                .to_compile_error()
                .into();
        }
    };

    let mut get_type_pairs = Vec::new();
    let mut serialize_match_arms = Vec::new();
    let mut get_name_match_arms = Vec::new();
    let mut from_schema_value_match_arms = Vec::new();
    let mut wire_cases = Vec::new();
    let mut stream_types = Vec::new();

    for variant in data_enum.variants.iter() {
        let variant_ident = &variant.ident;
        let variant_name = variant_ident.to_string();

        // Only support single-field tuple variants
        match &variant.fields {
            Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
                let field_type = &fields.unnamed[0].ty;
                stream_types.push(field_type);

                wire_cases.push(quote! {
                    golem_rust::schema::wit::wire::VariantCaseType {
                        name: #variant_name.to_string(),
                        payload: Some(<#field_type as golem_rust::WireSchema>::append_schema(builder)),
                        metadata: golem_rust::schema::wit::direct::empty_metadata(),
                    }
                });

                get_type_pairs.push(quote! {
                    (#variant_name.to_string(),  <#field_type as golem_rust::agentic::Schema>::get_type().get_schema_graph().expect("multimodal types cannot be nested"))
                });

                serialize_match_arms.push(quote! {
                    #enum_name::#variant_ident(inner) => {
                        (#variant_name.to_string(), <#field_type as golem_rust::agentic::Schema>::to_schema_value(inner)?)
                    }
                });

                (get_name_match_arms).push(quote! {
                    #enum_name::#variant_ident(_) => #variant_name.to_string()
                });

                from_schema_value_match_arms.push(quote! {
                    #variant_name => {
                        let val = <#field_type as golem_rust::agentic::Schema>::from_schema_value(
                            value,
                            <#field_type as golem_rust::agentic::Schema>::get_type(),
                        )?;
                        Ok(#enum_name::#variant_ident(val))
                    }
                });
            }
            _ => {
                return syn::Error::new_spanned(
                    variant,
                    "Multimodal derive only supports single-field tuple variants",
                )
                .to_compile_error()
                .into();
            }
        }
    }

    let expanded = quote! {
        impl golem_rust::agentic::MultimodalWire for #enum_name {
            fn contains_stream(seen: &mut ::std::collections::HashSet<&'static str>) -> bool {
                if !seen.insert(::core::any::type_name::<Self>()) {
                    return false;
                }
                false #(|| <#stream_types as golem_rust::WireSchema>::contains_stream(seen))*
            }

            fn append_modality_cases(
                builder: &mut golem_rust::schema::wit::direct::WireSchemaBuilder,
            ) -> Vec<golem_rust::schema::wit::wire::VariantCaseType> {
                vec![#(#wire_cases),*]
            }
        }

        impl golem_rust::agentic::MultimodalSchema for #enum_name {
            fn get_multimodal_schema() -> Vec<(String, golem_rust::schema::SchemaGraph)> {
                vec![
                    #(#get_type_pairs),*
                ]
            }

            fn to_schema_value(self) -> Result<(String, golem_rust::SchemaValue), String> {
                let result = match self {
                    #(#serialize_match_arms),*
                };
                Ok(result)
            }

            fn get_name(&self) -> String {
                match self {
                    #(#get_name_match_arms),*
                }
            }

            fn from_schema_value(name: String, value: golem_rust::SchemaValue) -> Result<Self, String> {
                 match name.as_str() {
                    #(#from_schema_value_match_arms),*,
                    _ => return Err(format!("Unknown modality: {}", name))
                 }
            }
        }
    };

    TokenStream::from(expanded)
}