beam: fix Aho-Corasick empty-pattern handling (emit at every position)

wizard-work/beam/aho_corasick.py

@@ -58,14 +58,14 @@ class AhoCorasick:
             for pi in self.out[node]:
                 plen = len(self.patterns[pi])
                 if plen == 0:
-                    start = i
-                else:
-                    start = i + 1 - plen
+                    continue  # handled below for every position
+                start = i + 1 - plen
                 res.append((start, pi))
-        # empty patterns also match at the end position
+        # empty patterns match at every position 0..n
         for pi, p in enumerate(self.patterns):
             if p == "":
-                res.append((n, pi))
+                for pos in range(n + 1):
+                    res.append((pos, pi))
         res.sort(key=lambda x: (x[0], x[1]))
         return res