Function normalize_pattern_for_base_for 

pub fn normalize_pattern_for_base_for(
    pattern: &str,
    base: Option<&Path>,
    windows: bool,
) -> String

normalize_pattern_for_base for an explicit platform (see prepare_pattern_for).

. and .. components are resolved first (see normalize_dot_segments). A leading ! is an ignore override negation, not part of the path: it is set aside while the operand is prepared and put back. The pattern is left with its dots where resolving them would turn a positive include into a comment (#) or a negation (!) line.