martin-g commented on code in PR #398:
URL: https://github.com/apache/avro-rs/pull/398#discussion_r2681739064
##########
avro_derive/src/lib.rs:
##########
@@ -264,6 +283,69 @@ fn get_data_enum_schema_def(
}
}
+/// Generate a schema definition for a type marked transparent.
+fn get_transparent_data_schema_def(
+ data: &syn::Data,
+ input_span: Span,
+) -> Result<TokenStream, Vec<syn::Error>> {
+ match data {
+ syn::Data::Struct(data_struct) => match &data_struct.fields {
+ syn::Fields::Named(fields_named) => {
+ if fields_named.named.len() != 1 {
+ return Err(vec![syn::Error::new(
+ input_span,
+ "#[serde(transparent)] is only allowed on structs with
one field",
+ )]);
+ }
+ let field = fields_named
+ .named
+ .first()
+ .expect("There is exactly one field");
+ let field_attrs = FieldOptions::new(&field.attrs,
field.span())?;
+ if field_attrs != FieldOptions::default() {
+ return Err(vec![syn::Error::new(
+ input_span,
+ "#[serde(transparent)] is incompatible with all other
attributes",
+ )]);
+ }
+ let ty = &field.ty;
+ Ok(quote! {
+ #ty::get_schema_in_ctxt(named_schemas, enclosing_namespace)
+ })
+ }
+ syn::Fields::Unnamed(_) => Err(vec![syn::Error::new(
+ input_span,
+ "AvroSchema derive does not work for tuple structs",
+ )]),
+ syn::Fields::Unit => Err(vec![syn::Error::new(
+ input_span,
+ "AvroSchema derive does not work for unit structs",
+ )]),
+ },
+ syn::Data::Enum(data_enum) => {
+ if data_enum
+ .variants
+ .iter()
+ .all(|v| syn::Fields::Unit == v.fields)
+ {
+ Err(vec![syn::Error::new(
+ input_span,
+ "AvroSchema derive does not support #[serde(transparent)]
on simple enums",
+ )])
+ } else {
+ Err(vec![syn::Error::new(
+ input_span,
+ "AvroSchema derive does not work for enums with non unit
structs",
+ )])
+ }
+ }
+ syn::Data::Union(_) => Err(vec![syn::Error::new(
+ input_span,
+ "AvroSchema derive only works for structs and simple enums",
Review Comment:
This error is returned by get_transparent_data_schema_def(), so it is
special for the `transparent` attribute.
The generic error is at
https://github.com/apache/avro-rs/blob/6b9a15f7db96b165cb6839dc9a655fdf1b5b7ddb/avro_derive/src/lib.rs#L91
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