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| 1 | +use proc_macro::TokenStream; |
| 2 | +use quote::quote; |
| 3 | +use syn::spanned::Spanned; |
| 4 | +use syn::{Attribute, Data, DeriveInput, Fields, Ident, Meta, Result, Variant, parse_macro_input}; |
| 5 | + |
| 6 | +#[proc_macro_derive(MessageBusinessRef, attributes(business_ref))] |
| 7 | +pub fn derive_message_business_ref(input: TokenStream) -> TokenStream { |
| 8 | + let input = parse_macro_input!(input as DeriveInput); |
| 9 | + match expand_message_business_ref(input) { |
| 10 | + Ok(tokens) => tokens.into(), |
| 11 | + Err(error) => error.into_compile_error().into(), |
| 12 | + } |
| 13 | +} |
| 14 | + |
| 15 | +fn expand_message_business_ref(input: DeriveInput) -> Result<proc_macro2::TokenStream> { |
| 16 | + let enum_name = input.ident; |
| 17 | + let Data::Enum(data) = input.data else { |
| 18 | + return Err(syn::Error::new( |
| 19 | + enum_name.span(), |
| 20 | + "MessageBusinessRef can only be derived for enums", |
| 21 | + )); |
| 22 | + }; |
| 23 | + |
| 24 | + let match_arms = data.variants.iter().map(expand_variant).collect::<Result<Vec<_>>>()?; |
| 25 | + |
| 26 | + Ok(quote! { |
| 27 | + impl HasBusinessRef for #enum_name { |
| 28 | + fn business_ref(&self) -> BusinessRef { |
| 29 | + match self { |
| 30 | + #(#match_arms),* |
| 31 | + } |
| 32 | + } |
| 33 | + } |
| 34 | + }) |
| 35 | +} |
| 36 | + |
| 37 | +fn expand_variant(variant: &Variant) -> Result<proc_macro2::TokenStream> { |
| 38 | + let scope = business_ref_scope(variant)?; |
| 39 | + let variant_name = &variant.ident; |
| 40 | + |
| 41 | + match scope.as_str() { |
| 42 | + "graph" => { |
| 43 | + let binding = tuple_payload_binding(variant)?; |
| 44 | + Ok(quote! { |
| 45 | + Self::#variant_name(#binding) => BusinessRef::Graph { |
| 46 | + instance_id: #binding.instance_id, |
| 47 | + graph_id: #binding.graph_id, |
| 48 | + } |
| 49 | + }) |
| 50 | + } |
| 51 | + "instance" => { |
| 52 | + let binding = tuple_payload_binding(variant)?; |
| 53 | + Ok(quote! { |
| 54 | + Self::#variant_name(#binding) => BusinessRef::Instance { |
| 55 | + instance_id: #binding.instance_id, |
| 56 | + } |
| 57 | + }) |
| 58 | + } |
| 59 | + "unscoped" => match &variant.fields { |
| 60 | + Fields::Unit => Ok(quote! { |
| 61 | + Self::#variant_name => BusinessRef::Unscoped |
| 62 | + }), |
| 63 | + Fields::Unnamed(_) => Ok(quote! { |
| 64 | + Self::#variant_name(..) => BusinessRef::Unscoped |
| 65 | + }), |
| 66 | + Fields::Named(_) => Ok(quote! { |
| 67 | + Self::#variant_name { .. } => BusinessRef::Unscoped |
| 68 | + }), |
| 69 | + }, |
| 70 | + _ => unreachable!("business_ref_scope validates accepted values"), |
| 71 | + } |
| 72 | +} |
| 73 | + |
| 74 | +fn tuple_payload_binding(variant: &Variant) -> Result<Ident> { |
| 75 | + match &variant.fields { |
| 76 | + Fields::Unnamed(fields) if fields.unnamed.len() == 1 => { |
| 77 | + Ok(Ident::new("message", variant.span())) |
| 78 | + } |
| 79 | + _ => Err(syn::Error::new( |
| 80 | + variant.span(), |
| 81 | + "graph and instance business references require exactly one payload field", |
| 82 | + )), |
| 83 | + } |
| 84 | +} |
| 85 | + |
| 86 | +fn business_ref_scope(variant: &Variant) -> Result<String> { |
| 87 | + let mut matching = variant |
| 88 | + .attrs |
| 89 | + .iter() |
| 90 | + .filter(|attribute: &&Attribute| attribute.path().is_ident("business_ref")); |
| 91 | + let Some(attribute) = matching.next() else { |
| 92 | + // Point at the offending variant rather than the derive site, so the |
| 93 | + // compiler error names the variant that lacks an attribute. |
| 94 | + return Err(syn::Error::new( |
| 95 | + variant.ident.span(), |
| 96 | + "each message variant must declare #[business_ref(graph)], #[business_ref(instance)], or #[business_ref(unscoped)]", |
| 97 | + )); |
| 98 | + }; |
| 99 | + if matching.next().is_some() { |
| 100 | + return Err(syn::Error::new(attribute.span(), "duplicate business_ref attribute")); |
| 101 | + } |
| 102 | + |
| 103 | + let Meta::List(list) = &attribute.meta else { |
| 104 | + return Err(syn::Error::new( |
| 105 | + attribute.span(), |
| 106 | + "business_ref must be written as #[business_ref(graph)], #[business_ref(instance)], or #[business_ref(unscoped)]", |
| 107 | + )); |
| 108 | + }; |
| 109 | + let scope: Ident = list.parse_args()?; |
| 110 | + let scope = scope.to_string(); |
| 111 | + if matches!(scope.as_str(), "graph" | "instance" | "unscoped") { |
| 112 | + Ok(scope) |
| 113 | + } else { |
| 114 | + Err(syn::Error::new(attribute.span(), "business_ref must be graph, instance, or unscoped")) |
| 115 | + } |
| 116 | +} |
| 117 | + |
| 118 | +#[cfg(test)] |
| 119 | +mod tests { |
| 120 | + use super::*; |
| 121 | + use syn::parse_quote; |
| 122 | + |
| 123 | + fn expand_error(input: DeriveInput) -> String { |
| 124 | + expand_message_business_ref(input).unwrap_err().to_string() |
| 125 | + } |
| 126 | + |
| 127 | + #[test] |
| 128 | + fn rejects_non_enum_input() { |
| 129 | + let input = parse_quote! { |
| 130 | + struct Message; |
| 131 | + }; |
| 132 | + |
| 133 | + assert_eq!(expand_error(input), "MessageBusinessRef can only be derived for enums"); |
| 134 | + } |
| 135 | + |
| 136 | + #[test] |
| 137 | + fn requires_a_business_ref_scope_for_every_variant() { |
| 138 | + let input = parse_quote! { |
| 139 | + enum Message { |
| 140 | + Missing(Payload), |
| 141 | + } |
| 142 | + }; |
| 143 | + |
| 144 | + assert_eq!( |
| 145 | + expand_error(input), |
| 146 | + "each message variant must declare #[business_ref(graph)], #[business_ref(instance)], or #[business_ref(unscoped)]" |
| 147 | + ); |
| 148 | + } |
| 149 | + |
| 150 | + #[test] |
| 151 | + fn rejects_invalid_or_duplicate_scopes() { |
| 152 | + let invalid = parse_quote! { |
| 153 | + enum Message { |
| 154 | + #[business_ref(other)] |
| 155 | + Invalid(Payload), |
| 156 | + } |
| 157 | + }; |
| 158 | + assert_eq!(expand_error(invalid), "business_ref must be graph, instance, or unscoped"); |
| 159 | + |
| 160 | + let duplicate = parse_quote! { |
| 161 | + enum Message { |
| 162 | + #[business_ref(graph)] |
| 163 | + #[business_ref(instance)] |
| 164 | + Duplicate(Payload), |
| 165 | + } |
| 166 | + }; |
| 167 | + assert_eq!(expand_error(duplicate), "duplicate business_ref attribute"); |
| 168 | + } |
| 169 | + |
| 170 | + #[test] |
| 171 | + fn graph_and_instance_scopes_require_one_tuple_payload() { |
| 172 | + let named = parse_quote! { |
| 173 | + enum Message { |
| 174 | + #[business_ref(graph)] |
| 175 | + Graph { payload: Payload }, |
| 176 | + } |
| 177 | + }; |
| 178 | + assert_eq!( |
| 179 | + expand_error(named), |
| 180 | + "graph and instance business references require exactly one payload field" |
| 181 | + ); |
| 182 | + |
| 183 | + let multiple = parse_quote! { |
| 184 | + enum Message { |
| 185 | + #[business_ref(instance)] |
| 186 | + Instance(Payload, Payload), |
| 187 | + } |
| 188 | + }; |
| 189 | + assert_eq!( |
| 190 | + expand_error(multiple), |
| 191 | + "graph and instance business references require exactly one payload field" |
| 192 | + ); |
| 193 | + } |
| 194 | + |
| 195 | + #[test] |
| 196 | + fn accepts_all_unscoped_variant_shapes() { |
| 197 | + let input = parse_quote! { |
| 198 | + enum Message { |
| 199 | + #[business_ref(unscoped)] |
| 200 | + Unit, |
| 201 | + #[business_ref(unscoped)] |
| 202 | + Tuple(u8, u16), |
| 203 | + #[business_ref(unscoped)] |
| 204 | + Named { value: u8 }, |
| 205 | + } |
| 206 | + }; |
| 207 | + |
| 208 | + assert!(expand_message_business_ref(input).is_ok()); |
| 209 | + } |
| 210 | +} |
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