utilise nfa size limits to prevent oom

Author: addisoncrump

fuzz/fuzz_targets/ast_diff_default.rs

@@ -3,7 +3,7 @@
 use {
     libfuzzer_sys::{fuzz_target, Corpus},
     regex::RegexBuilder,
-    regex_automata::nfa::thompson::pikevm::PikeVM as NfaRegex,
+    regex_automata::nfa::thompson::{pikevm::PikeVM as NfaRegex, NFA},
     regex_syntax::ast::Ast,
 };
 
@@ -26,11 +26,15 @@ fuzz_target!(|data: FuzzData| -> Corpus {
     let _ = env_logger::try_init();
 
     let pattern = format!("{}", data.ast);
-    let Ok(re) = RegexBuilder::new(&pattern).size_limit(1<<20).build() else {
+    let Ok(re) = RegexBuilder::new(&pattern).size_limit(1 << 20).build() else {
         return Corpus::Reject;
     };
-    let Ok(baseline) = NfaRegex::new(&pattern) else {
-        return Corpus::Reject; // should we error here?
+    let config = NFA::config().nfa_size_limit(Some(1 << 20));
+    let Ok(nfa) = NFA::compiler().configure(config).build(&pattern) else {
+        return Corpus::Reject;
+    };
+    let Ok(baseline) = NfaRegex::new_from_nfa(nfa) else {
+        return Corpus::Reject;
     };
     let mut cache = baseline.create_cache();