Function normalize_pattern_for_base 

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

Normalize a config path pattern for matching against paths discovered under base: expand a leading ~, then rewrite an absolute pattern as one relative to base when base contains it.

The rewrite is what makes an absolute pattern usable as a walker override: the ignore crate reads a leading / as “anchored to the walk base”, so /home/dev/docs/** would otherwise be understood as <base>/home/dev/docs/** and match nothing. A pattern pointing outside base is left absolute - nothing under this walk can match it, which is the correct outcome.

A pattern can also name base’s location through a symlink (/var/folders/… for a base at /private/var/folders/…), which no strip of base in either form removes. Its leading literal components are then resolved, giving the same location in the base’s own spelling. Only that prefix is rewritten and the strip consumes it, so what survives is the pattern as written. A pattern whose first component holds a wildcard or a brace alternation has no such prefix and stays absolute.