I’m working through the dtolnay proc-macro-workshop to learn about Rust procedural macros. As part of an exercise, I’m trying to create a derive macro that generates a builder struct for each struct annotated with the #[derive(Builder)] macro.

I’m working on a Rust procedural macro and encountering an issue while parsing an attribute. The goal is to ensure the attribute follows a specific structure and to extract an expression from it. However, I’m getting an Err object when parsing the attribute even though it appears to be correctly set.