Valid prefix search (with ^) goes into dead state #1169
Description
What version of regex are you using?
regex-automata = "0.4.5"
Describe the bug at a high level.
I'm trying to do a prefix search by adding a ^ at the beginning of my pattern. I'm searching right-to-left, but the dfa is failing to find a match and entering the "dead" state.
What are the steps to reproduce the behavior?
use regex_automata::{hybrid::dfa::DFA, nfa::thompson, Input}; use std::error::Error; fn main() -> Result<(), Box<dyn Error>> { let pattern = r"^Qu"; let dfa = DFA::builder() .thompson(thompson::Config::new().reverse(true)) .build_many(&[pattern])?; let mut cache = dfa.create_cache(); let hay = "Quartz"; let mut state = dfa.start_state_reverse(&mut cache, &Input::new(hay))?; for &b in hay.as_bytes().iter().rev() { state = dfa.next_state(&mut cache, state, b)?; if state.is_dead() { panic!("DEAD"); } if state.is_match() { println!("BREAK"); break; } } state = dfa.next_eoi_state(&mut cache, state)?; assert!(state.is_match()); Ok(()) }What is the actual behavior?
❯ cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.00s Running `target/debug/reg` thread 'main' panicked at src/main.rs:17:13: DEAD note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace What is the expected behavior?
I expect the program to run through to the end, finding a match and passing the assertion, as the pattern ^Qu should match the string "Quartz".
If I remove the ^ from the pattern, this program behaves as expected.