synsert

A primitive for programatically editing files using [syn].

syn is the de-facto standard for parsing Rust. Its syntax tree is easy to use, but it is lossy - if you parse a file, edit it with syn, and unparse it, you'll lose all your comments and spacing (for example).

Rust Analyzer's syntax crate has a lossless syntax tree, which powers IDE assists, but it's far more difficult to use.

[Editor] allows you to use syn's syntax tree to write your Structured Search and Replace tools, or IDE assists.

let source_code = "const NUM: usize = 1;"; // get the source text

// create an AST and a helper struct from the same source code
let (mut editor, ast) = synsert::Editor::new_with_ast::<syn::ItemConst>(source_code).unwrap();

let edited = editor
    .append(ast.ident, "_YAKS")
    .replace(ast.expr, "9001")
    .finish();

assert_eq!(edited, "const NUM_YAKS: usize = 9001;");

See the examples for a more in-depth case using a syn::visit::Visitor