syn-locator

syn-locator helps you to find source code locations of syn nodes.

When to use

If you read a rust file then parse the read string through the syn::parse_str, you will lose span information. This crate finds source code locations of syntax tree nodes by simple string comparison.

Example

    use syn_locator::*;

    // Assumes that we read this code from a file.
    let file_path = "/path/to/file.rs";
    let code = r"
        struct Foo {
            a: i32,
        }
    ";
    let syn = syn::parse_str::<syn::File>(code).unwrap();

    // Finds location of the syntax tree.
    let syn = std::pin::Pin::new(&syn);
    syn.locate_as_entry(file_path, code.to_owned());

    // Picks a syntax tree node.
    let item_struct = match &syn.items[0] {
        syn::Item::Struct(item_struct) => item_struct,
        _ => unreachable!()
    };
    let field_ty = &item_struct.fields.iter().next().unwrap().ty;

    // Then, we can get some info from the syntax tree node.
    assert_eq!(field_ty.location(), Location {
        file_path,
        start: 37, // Byte offset
        end: 40 // Byte offset
    });
    assert_eq!(field_ty.location_message(), "/path/to/file.rs:3: i32");