Function rustc_parse_format::find_width_map_from_snippet

pub(crate) fn find_width_map_from_snippet(
    input: &str,
    snippet: Option<String>,
    str_style: Option<usize>,
) -> InputStringKind

Finds the indices of all characters that have been processed and differ between the actual written code (code snippet) and the InternedString that gets processed in the Parser in order to properly synthesise the intra-string Spans for error diagnostics.