Function estimate_nfa_states 

fn estimate_nfa_states(pattern: &MatchRecognizePattern) -> u64

Upper bound on the number of NFA states Nfa::compile will allocate for pattern.

Mirrors the construction in nfa.rs (Nfa::build): a variable is 2 states; an alternation adds a start and an accept state; *, ? and each optional copy of a range add 2; + builds the inner pattern twice; PERMUTE of n variables becomes an alternation of n! concatenations. Saturating throughout, so an over-large pattern reports a saturated estimate rather than wrapping.

This is a model of code in another crate, so it cannot be checked by a test: risingwave_stream depends on risingwave_frontend’s protos, not the reverse, and nothing can observe both. If the state count of any construct in nfa.rs changes, this must change with it, or the guard above silently becomes an under-estimate. The construction sites in nfa.rs carry a comment pointing back here.