Change literal extraction for look-arounds

Author: shilangyu

regex-automata/src/meta/strategy.rs

@@ -258,6 +258,11 @@ impl Pre<()> {
         if !info.props()[0].look_set().is_empty() {
             return None;
         }
+        // For a similar reason, we require that it has zero look-around
+        // expressions.
+        if info.props()[0].contains_lookaround_expr() {
+            return None;
+        }
         // Finally, currently, our prefilters are all oriented around
         // leftmost-first match semantics, so don't try to use them if the
         // caller asked for anything else.

regex-syntax/src/hir/literal.rs

@@ -172,8 +172,9 @@ impl Extractor {
         use crate::hir::HirKind::*;
 
         match *hir.kind() {
-            Empty | Look(_) => Seq::singleton(self::Literal::exact(vec![])),
-            LookAround(_) => Seq::infinite(),
+            Empty | Look(_) | LookAround(_) => {
+                Seq::singleton(self::Literal::exact(vec![]))
+            }
             Literal(hir::Literal(ref bytes)) => {
                 let mut seq =
                     Seq::singleton(self::Literal::exact(bytes.to_vec()));