pub fn required_trigrams(pattern: &str) -> Option<Vec<Trigram>>Expand description
Extract the mandatory trigram conjunction for pattern, or None if the
pattern is too complex to prove a mandatory literal (caller must full-scan).
Safety contract: a returned trigram set is required — every document
matching pattern contains all of them — so intersecting their postings can
never drop a true match. When that cannot be proven, this returns None.