Simple helper to register macro handler and process their input from build.rs Currently supports only function-like macro.
Useful when your macro should output a file, but you want to avoid race conditions during incremental compilation and other routines.
Uses [`syn`](https://crates.io/crates/syn) to parse files and visit their macros.
Imagine you have some macro `css` that implements scoping css technic.
It processes CSS syntax and returns css_class. But you also need to aggregate all `css`!` calls and save them into `style.css`
```rust
fn main() {
use rcss::css as my_css;
let css_class = my_css!{
.container {
background-color: black;
}
};
let html = format!(r#"<div class="{} my-class">Hello</div>"#, css_class);
let html = format!(r#"<link rel="stylesheet" href="style.css" />{}"#, html);
// output html.
}
```
In order to aggregate all CSS, you should open all src files,
find if `css!`` was used and handle their input.
You also should handle imports and renames.
The target of this crate is to deal with these problems.
In build.rs
```rust
fn main () {
let project_path = std::env!("CARGO_MANIFEST_DIR");
let crate_name = std::env::var("CARGO_CRATE_NAME").unwrap_or("rcss".to_owned());
let collect_style = RefCell::new(String::new());
let mut css_handler = |context, token_stream: TokenStream| {
collect_style.borrow_mut().push_str(/* Handle token_stream */ )
};
let mut visitor = Visitor::new();
let css_macro_path = vec![format!("{crate_name}::css")];
let css_macro = Rc::new(RefCell::new(MacroCall::new(&mut css_handler)));
visitor.add_macro(css_macro_path, css_macro);
visitor.visit_project(project_path);
let content = collect_style.into_inner();
// .. save content to a file
}
```
`macro-visit` will find all occurrences of `css!` macro, even if it was renamed.
Currently, it only looks for imports inside one file at a time and does not parallelize file processing.