How to inject the AST location

[machaval]

I'm writing a parser and I have as a requirement that the AST has the location of the node in the text.
I'm not able to find an example that does this

[kevinmehall]

position!() matches the empty string and returns the current offset into the input. See https://github.com/signalspec/signalspec/blob/master/src/syntax/grammar.rs for a complete example of using it to attach spans to AST nodes.