expander

Expands a proc-macro into a file, and uses a include! directive in place.

Usage

In your proc-macro, use it like:

```rust

[procmacroattribute]

fn foo(attr: procmacro::TokenStream, input: procmacro::TokenStream) -> procmacro::TokenStream { // wrap as per usual for proc-macro2::TokenStream, here dropping attr for simplicity foo2(input.into()).into() }

// or any other macro type fn foo2(input: procmacro2::TokenStream) -> procmacro2::TokenStream { let modified = quote::quote!{ #[derive(Debug, Clone, Copy)] struct X { y: [u8:32], } };

let expanded = Expander::new("bar.rs")
    .add_comment("This is generated code!".to_owned())
    .fmt(Edition::_2021)
    // common way of gating this, by making it part of the default feature set
    .dry(cfg!(feature="no-file-expansion"))
    .write_to_out_dir(ts.clone())?;
expanded

} ```

will expand into

rust include!("/absolute/path/to/your/project/target/debug/build/expander-49db7ae3a501e9f4/out/bar.rs");

where the file content will be

```rust

[derive(Debug, Clone, Copy)]

struct X { y: [u8:32], } ```

Advantages

• Only expands a particular proc-macro, not all of them. I.e. tracing is notorious for expanding into a significant amount of boilerplate with i.e. cargo expand
• Get good errors when your generated code is not perfect yet