This repo demonstrates a way to organize packages that whose purpose is to generate Rust code. Typically this will entail an external input that is then processed and transformed. Packages that do this often choose to expose this code generation via a proc_macro or via a builder for use in a build.rs file. The former doesn't require the creation on a specific build step and so may be simpler, while the latter produces code that's easier to examine (without resorting to cargo expands for example).

The constructs here are designed to let a single codegen implementation be used either from a macro or from build.rs (or some other tool to produce file artifacts with the generated code).

There are three crates:

• codegen-impl is where the real work happens. This is where code generation actually happens.
• codegen-macro exports a proc_macro. It depends on codegen-impl and invokes the functions exposed by it to do the code generation. Note that packages may either define macros or other items to export so this package is necessary for the subsequent package to export both macros and other items.
• codegen is the front-end package intended for direct use by consumrs. It exposes both the macros from codegen-macro as well as the functionality from codegen-impl (either directly or wrapped in APIs better suited for its intended use).

To demonstrage the use of these, check out

• example-build which uses a build.rs file to generate code, or...
• example-macro which generates code via the macros.