Rust macros come in a few flavors. One of them is procedural macros. The one most interesting to me for the Open Feature project is procedural attribute macros, which work similar to java annotations (but allow the rewriting of source code, which I haven’t done w/ java).
The https://crates.io/crates/darling library appears to ease the parsing of attributes passed to macros into a struct, similar to how serde works.