Function parse_recipe_at 

pub fn parse_recipe_at(
    text: &str,
    name: &str,
    scale: f64,
    file: Option<&Utf8Path>,
) -> Result<Outcome<Recipe>, CoreError>

As parse_recipe, but attributing diagnostics to a specific file path.

Pass file when the text came from disk, so that diagnostics point at something the caller can open. An editor parsing an unsaved buffer passes None and still gets spans.