Crate procss

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A simple CSS parsing and transformation framework. Procss can be used to quickly bundle a collection of CSS+ files, or write your own custom transforms.


Procss’s parser understands a nested superset of CSS (which we refer to as CSS+), similar to the CSS nesting proposal, or languages like Sass. Start with source CSS+ as a str, use crate::parse or crate::parse_unchecked to generate an ast::Tree.

use procss::{ast, parse};

let ast = procss::parse("div{.open{color:red;}}").unwrap();

The resulting ast::Tree can be converted to a de-nested ast::Css with the ast::Tree::flatten_tree method, which itself can then be rendered as a plain browser-readable CSS string via the RenderCss::as_css_string trait method.

use procss::RenderCss;

let flat: ast::Css = ast.flatten_tree();
let css: String = flat.as_css_string();
assert_eq!(css, "div .open{color:red;}");

Intermediate structs ast::Css::transform amd ast::Tree::transform can be used to recursively mutate a tree for a variety of node structs in the ast module. Some useful Example of such transforms can be found in the transformers module.

use procss::transformers;

let test = "
@mixin test {color: red;}
div {@include test;}

let mut ast = procss::parse(test).unwrap();
transformers::apply_mixin(&mut ast);
let flat = ast.flatten_tree().as_css_string();
assert_eq!(flat, "div{color:red;}");

For coordinating large builds on a tree of CSS files, the BuildCss struct can parse and minify, applying all transforms (including transformers::apply_import) as the compilation is left-folded over the inputs.

let mut build = procss::BuildCss::new("./src");
build.add_file("logout.scss"); // imports "controls/menu.scss"
build.add_file("my_app.scss"); // imports "controls/menu.scss" and "logout.scss"



  • A CSS+ project build, comprising a collection of CSS+ files which may reference eachother (via @import).



  • Parse CSS text to a Tree (where it can be further manipulated), capturing detailed error reporting for a moderate performance impact (using nom::error::VerboseError).
  • Parse CSS text to a Tree, without capturing error details, for maximum performance without any error details when parsing fails.