santiagomed commented on code in PR #3414:
URL: https://github.com/apache/thrift/pull/3414#discussion_r3127429489
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compiler/cpp/src/thrift/generate/t_rs_generator.cc:
##########
@@ -1699,10 +1699,37 @@ void t_rs_generator::render_struct_sync_read(const
string& struct_name,
for (members_iter = members.begin(); members_iter != members.end();
++members_iter) {
t_field* tfield = (*members_iter);
+ t_type* resolved = get_true_type(tfield->get_type());
+ bool is_union_field = resolved->is_struct() &&
((t_struct*)resolved)->is_union();
f_gen_ << indent() << rust_safe_field_id(tfield->get_key()) << " => {"
<< '\n';
indent_up();
- render_type_sync_read("val", tfield->get_type());
- f_gen_ << indent() << struct_field_read_temp_variable(tfield) << " =
Some(val);" << '\n';
+ if (is_union_field) {
+ // Union fields: catch "received empty union" errors from unknown
+ // variants and treat them as None for forward compatibility.
+ // This matches how Java, Go, and Python Thrift handle unknown
+ // union fields -- they skip silently instead of failing.
+ //
+ // Use the resolved (non-Box) type for the method call since
+ // Box<T>::method() is not valid Rust syntax for turbofish.
+ string resolved_type = to_rust_type(resolved);
+ bool is_boxed_union = to_rust_type(tfield->get_type()) !=
resolved_type;
+ string read_call(resolved_type + "::read_from_in_protocol(i_prot)");
+ string val_expr = is_boxed_union ? "Box::new(val)" : "val";
+ f_gen_ << indent() << "match " << read_call << " {" << '\n';
+ indent_up();
+ f_gen_ << indent() << "Ok(val) => { " <<
struct_field_read_temp_variable(tfield) << " = Some(" << val_expr << "); }," <<
'\n';
+ f_gen_ << indent() << "Err(thrift::Error::Protocol(ref e)) if
e.message.contains(\"received empty union\") => {" << '\n';
Review Comment:
I added `ProtocolErrorKind::EmptyUnion = 7` to the runtime library and
updated both sides of the codegen to use it. The union deserializer now emits
`EmptyUnion` instead of `InvalidData`, and the struct-level catch arm matches
on `e.kind == ProtocolErrorKind::EmptyUnion` instead of the string check. Also
added an integration test covering the unknown variant path.
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