add sparse dfa

Author: addisoncrump

fuzz/Cargo.toml

@@ -75,6 +75,10 @@ path = "fuzz_targets/ast_diff_default.rs"
 name = "ast_diff_dense_dfa"
 path = "fuzz_targets/ast_diff_dense_dfa.rs"
 
+[[bin]]
+name = "ast_diff_sparse_dfa"
+path = "fuzz_targets/ast_diff_sparse_dfa.rs"
+
 [[bin]]
 name = "ast_diff_nfas"
 path = "fuzz_targets/ast_diff_nfas.rs"

fuzz/fuzz_targets/ast_diff_sparse_dfa.rs

@@ -0,0 +1,66 @@
+#![no_main]
+
+use {
+    libfuzzer_sys::{fuzz_target, Corpus},
+    regex_automata::{
+        dfa::{dense::DFA, regex::Builder as RegexBuilder},
+        nfa::thompson::{pikevm::PikeVM as NfaRegex, NFA},
+    },
+    regex_syntax::ast::Ast,
+};
+
+#[derive(Eq, PartialEq, arbitrary::Arbitrary)]
+struct FuzzData {
+    ast: Ast,
+    haystack: String,
+}
+
+impl std::fmt::Debug for FuzzData {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut builder = f.debug_struct("FuzzData");
+        builder.field("ast", &format!("{}", self.ast));
+        builder.field("haystack", &self.haystack);
+        builder.finish()
+    }
+}
+
+fn do_fuzz(data: FuzzData) -> Corpus {
+    let _ = env_logger::try_init();
+
+    let pattern = format!("{}", data.ast);
+    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();
+
+    let config = DFA::config().dfa_size_limit(Some(1 << 20));
+    let Ok(dense_re) = RegexBuilder::new().dense(config).build(&pattern) else {
+        return Corpus::Reject;
+    };
+    let (Ok(fwd), Ok(rev)) = (dense_re.forward().to_sparse(), dense_re.reverse().to_sparse()) else {
+        return Corpus::Reject;
+    };
+    let re = RegexBuilder::new().build_from_dfas(fwd, rev);
+
+    assert_eq!(
+        re.is_match(&data.haystack),
+        baseline.is_match(&mut cache, &data.haystack)
+    );
+    let found1 = re.find(&data.haystack);
+    let found2 = baseline.find(&mut cache, &data.haystack);
+    if let Some(found1) = found1 {
+        let found2 = found2.expect("Found in target, but not in baseline!");
+        assert_eq!(found1.start(), found2.start());
+        assert_eq!(found1.end(), found2.end());
+    }
+
+    // no captures
+
+    Corpus::Keep
+}
+
+fuzz_target!(|data: FuzzData| -> Corpus { do_fuzz(data) });