Fix anchors in lookarounds

Author: shilangyu

regex-automata/src/nfa/thompson/compiler.rs

@@ -2158,6 +2158,29 @@ mod tests {
         );
     }
 
+    #[test]
+    fn compile_yes_unanchored_prefix_with_start_anchor_in_lookaround() {
+        let nfa = NFA::compiler()
+            .configure(NFA::config().which_captures(WhichCaptures::None))
+            .build(r"(?<=^)a")
+            .unwrap();
+        assert_eq!(
+            nfa.states(),
+            &[
+                s_bin_union(2, 1),
+                s_range(0, 255, 0),
+                s_bin_union(3, 6),
+                s_bin_union(5, 4),
+                s_range(0, 255, 3),
+                s_look(Look::Start, 7),
+                s_check_lookaround(0, true, 8),
+                s_write_lookaround(0),
+                s_byte(b'a', 9),
+                s_match(0)
+            ]
+        );
+    }
+
     #[test]
     fn compile_empty() {
         assert_eq!(build("").states(), &[s_match(0),]);

regex-syntax/src/hir/mod.rs

@@ -2589,6 +2589,8 @@ impl Properties {
             literal: false,
             alternation_literal: false,
             contains_lookaround_expr: true,
+            look_set_prefix: LookSet::empty(),
+            look_set_suffix: LookSet::empty(),
             ..*sub_p.0.clone()
         };
         Properties(Box::new(inner))

testdata/lookaround.toml

@@ -58,6 +58,12 @@ regex = "(?<=c+)a|(?<=d+)a"
 haystack = "aabacadaccaddaea"
 matches = [[5, 6], [7, 8], [10, 11], [13, 14]]
 
+[[test]]
+name = "lookbehind with anchor"
+regex = "(?<=^c)a"
+haystack = "cacacaasdacabasdqwe"
+matches = [[1, 2]]
+
 [[test]]
 name = "lookbehind next to capture group"
 regex = "(?<=c)(a|b)(b|a)"