openapi_trait_shared/codegen/

compositions.rs

//! Generators for `oneOf` / `allOf` / `anyOf` schema compositions.
//!
//! - `oneOf` → Rust enum. Tagged via `#[serde(tag = "...")]` when the schema
//!   carries a `discriminator`; otherwise `#[serde(untagged)]`.
//! - `anyOf` → Rust enum, always `#[serde(untagged)]` (`oneOf` semantics without
//!   the exclusivity guarantee is rarely useful in typed Rust).
//! - `allOf` → Rust struct that merges its branches: `$ref` branches become
//!   `#[serde(flatten)]` fields; inline object branches inline their properties
//!   directly.
//!
//! `SchemaKind::Not` and `SchemaKind::Any` remain unsupported and continue to
//! fall back to `serde_json::Value` in [`super::types`].
//!
//! Inline (non-top-level) compositions are synthesized into top-level types
//! using a deterministic name derived from the enclosing context (object name +
//! property, operation id + role). The accumulated definitions are emitted
//! alongside the explicit `components/schemas` items so all generated types
//! live at module scope.

use heck::ToPascalCase;
use openapiv3::{Discriminator, ReferenceOr, Schema, SchemaKind, Type};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};

use super::schemas::{doc_attr, object_field_tokens};
use super::types::{ref_to_ident, schema_to_rust_type_ctx};

/// Generate a Rust enum type for a `oneOf` composition.
///
/// When a `discriminator` is present we emit an internally tagged enum
/// (`#[serde(tag = "...")]`); otherwise an untagged enum.
#[must_use]
pub fn generate_one_of(
    name: &str,
    variants: &[ReferenceOr<Schema>],
    discriminator: Option<&Discriminator>,
    description: Option<&String>,
    inline_types: &mut Vec<TokenStream>,
) -> TokenStream {
    generate_enum(name, variants, discriminator, description, inline_types)
}

/// Generate a Rust enum type for an `anyOf` composition.
///
/// Always untagged — we treat `anyOf` like a non-discriminated `oneOf` because
/// strict `anyOf` semantics (multiple branches may match) do not have a clean
/// representation in typed Rust.
#[must_use]
pub fn generate_any_of(
    name: &str,
    variants: &[ReferenceOr<Schema>],
    description: Option<&String>,
    inline_types: &mut Vec<TokenStream>,
) -> TokenStream {
    generate_enum(name, variants, None, description, inline_types)
}

/// Generate a Rust struct type for an `allOf` composition.
///
/// `$ref` branches become `#[serde(flatten)]` fields of the referenced type.
/// Inline object branches contribute their properties directly. Any other inline
/// branch falls back to `serde_json::Value` (we do not synthesize nested types
/// here — those are handled by the enum path via [`schema_to_rust_type_ctx`]).
#[must_use]
pub fn generate_all_of(
    name: &str,
    variants: &[ReferenceOr<Schema>],
    description: Option<&String>,
    inline_types: &mut Vec<TokenStream>,
) -> TokenStream {
    let ident = format_ident!("{}", name.to_pascal_case());
    let doc = doc_attr(&description.cloned());

    let mut fields: Vec<TokenStream> = Vec::new();
    let mut ref_field_counter = 0usize;

    for branch in variants {
        match branch {
            ReferenceOr::Reference { reference } => {
                ref_field_counter += 1;
                let field_ident = format_ident!("inner_{}", ref_field_counter);
                let ty = ref_to_ident(reference);
                fields.push(quote! {
                    #[serde(flatten)]
                    pub #field_ident: #ty,
                });
            }
            ReferenceOr::Item(schema) => {
                if let SchemaKind::Type(Type::Object(obj)) = &schema.schema_kind {
                    for (prop_name, prop_ref) in &obj.properties {
                        let is_required = obj.required.iter().any(|r| r == prop_name);
                        fields.push(object_field_tokens(
                            prop_name,
                            &prop_ref.clone().unbox(),
                            is_required,
                            name,
                            inline_types,
                        ));
                    }
                } else {
                    // Nested composition or non-object inline branch: flatten a
                    // synthesized type when possible, otherwise fall back.
                    ref_field_counter += 1;
                    let field_ident = format_ident!("inner_{}", ref_field_counter);
                    let parent = format!("{name}Inner{ref_field_counter}");
                    let ty = schema_to_rust_type_ctx(
                        &ReferenceOr::Item(schema.clone()),
                        true,
                        Some(&parent),
                        inline_types,
                    );
                    fields.push(quote! {
                        #[serde(flatten)]
                        pub #field_ident: #ty,
                    });
                }
            }
        }
    }

    quote! {
        #doc
        #[derive(
            ::core::fmt::Debug,
            ::core::clone::Clone,
            ::serde::Serialize,
            ::serde::Deserialize,
        )]
        pub struct #ident {
            #(#fields)*
        }
    }
}

/// Shared helper backing [`generate_one_of`] and [`generate_any_of`].
fn generate_enum(
    name: &str,
    variants: &[ReferenceOr<Schema>],
    discriminator: Option<&Discriminator>,
    description: Option<&String>,
    inline_types: &mut Vec<TokenStream>,
) -> TokenStream {
    let ident = format_ident!("{}", name.to_pascal_case());
    let doc = doc_attr(&description.cloned());

    let serde_attr = discriminator.map_or_else(
        || quote! { #[serde(untagged)] },
        |d| {
            let tag = &d.property_name;
            quote! { #[serde(tag = #tag)] }
        },
    );

    let variant_tokens: Vec<TokenStream> = variants
        .iter()
        .enumerate()
        .map(|(idx, branch)| build_enum_variant(name, idx, branch, discriminator, inline_types))
        .collect();

    quote! {
        #doc
        #[derive(
            ::core::fmt::Debug,
            ::core::clone::Clone,
            ::serde::Serialize,
            ::serde::Deserialize,
        )]
        #serde_attr
        pub enum #ident {
            #(#variant_tokens,)*
        }
    }
}

/// Build a single enum variant for a `oneOf` / `anyOf` branch.
fn build_enum_variant(
    parent: &str,
    idx: usize,
    branch: &ReferenceOr<Schema>,
    discriminator: Option<&Discriminator>,
    inline_types: &mut Vec<TokenStream>,
) -> TokenStream {
    match branch {
        ReferenceOr::Reference { reference } => {
            let target_name = reference.rsplit('/').next().unwrap_or(reference);
            let variant_ident = format_ident!("{}", target_name.to_pascal_case());
            let ty = ref_to_ident(reference);
            // For tagged enums the rename governs the discriminator value on
            // the wire; for untagged enums the variant name is structural and
            // the rename is a no-op (but harmless).
            let rename_attr = discriminator
                .and_then(|d| discriminator_key_for_ref(d, reference))
                .map_or_else(|| quote! {}, |k| quote! { #[serde(rename = #k)] });
            quote! {
                #rename_attr
                #variant_ident(#ty)
            }
        }
        ReferenceOr::Item(schema) => {
            let variant_ident = format_ident!("Variant{}", idx + 1);
            let parent_for_synth = format!("{parent}Variant{}", idx + 1);
            let ty = schema_to_rust_type_ctx(
                &ReferenceOr::Item(schema.clone()),
                true,
                Some(&parent_for_synth),
                inline_types,
            );
            quote! {
                #variant_ident(#ty)
            }
        }
    }
}

/// Look up the discriminator mapping key (the serde tag value) for a given
/// `$ref`. Matches both fully qualified refs and bare component names, mirroring
/// the `OpenAPI` spec which permits either form in `discriminator.mapping`.
fn discriminator_key_for_ref(d: &Discriminator, reference: &str) -> Option<String> {
    let bare = reference.rsplit('/').next().unwrap_or(reference);
    d.mapping
        .iter()
        .find(|(_, v)| *v == reference || *v == bare)
        .map(|(k, _)| k.clone())
}