Building Rust Procedural Macros from the Grounds Up

As someone who has spent a _lot_ of time writing declarative and procedural macros, the important thing to ask before digging into a macro is whether you need a procedural macro at all.

Complex proc macros absolutely do slow builds down. In many cases, a proc macro only need to be a stub that can delegate to a declarative macro.

You may not need to use syn/quote, but if you are doing any sort of processing/parsing of Rust code you pretty much need to.

FWIW, I really hope that the Rust project focused on finer-grained token matching in declarative macros so we can migrate most proc_macro code away. The macro system is powerful, but nowhere near where it needs to be.

During the development of Learnix operating system I needed to represent bitflags inside some structures.

While there were alternatives with 3rd party libraries, the goal of the project is to implement and learn as much as I can.

Most of the guides I found online explained the concept great, but created only a simple macro as an example. So I decided to write about it myself too, with a real usage to create a bitfields attribute proc-macro, that takes a struct and turns it into bitfields.

Hope you will have a great read!

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