Function extend_span_to_previous_binding

fn extend_span_to_previous_binding(
    sess: &Session,
    binding_span: Span,
) -> Option<Span>

Given a binding_span, return the span through to the comma or opening brace of the previous binding.

use foo::a::{a, b, c};
//            ^^--- binding span
//            |
//            returned span

use foo::{a, b, c};
//        --- binding span