From d1ef17d4fd18f02505063e71c8e57090a0798901 Mon Sep 17 00:00:00 2001
From: Mohammad Hijjawi <mohammad.hijjawi1997@gmail.com>
Date: Tue, 27 Oct 2026 21:41:14 +0000
Subject: [PATCH] fix(kws): ignore empty keyword entries in KwsCtcPrefixDecoder
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The keywords string is split on commas, so a trailing comma
("小云小云,"), a doubled comma, or an entry made only of punctuation
produced a keyword with no token ids. An empty token sequence matched
every hypothesis: decoding silence returned "detected" with score 1.0
for the empty keyword, and a non-empty hypothesis without the real
keyword could raise IndexError in is_sublist.

Skip keywords that map to no tokens and log a warning instead.
---
 funasr/utils/kws_utils.py |  5 +++++
 tests/test_kws_utils.py   | 35 ++++++++++++++++++++++++++++++++++-
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/funasr/utils/kws_utils.py b/funasr/utils/kws_utils.py
index 11de3238b8..59447361f0 100644
--- a/funasr/utils/kws_utils.py
+++ b/funasr/utils/kws_utils.py
@@ -117,6 +117,11 @@ def __init__(
         keywords_list = self.keywords_str.strip().replace(' ', '').split(',')
         for keyword in keywords_list:
             strs, indexs = query_token_set(keyword, token_table, seg_dict)
+            if len(indexs) == 0:
+                # An empty entry (e.g. from a trailing comma) would match every
+                # hypothesis, so skip it instead of reporting a false detection.
+                logging.warning(f"Skipping keyword {keyword!r}: it has no tokens to match.")
+                continue
             self.keywords_token[keyword] = {}
             self.keywords_token[keyword]['token_id'] = indexs
             self.keywords_token[keyword]['token_str'] = ''.join('%s ' % str(i) for i in indexs)
diff --git a/tests/test_kws_utils.py b/tests/test_kws_utils.py
index 79fe4cdc82..12e8fd1a88 100644
--- a/tests/test_kws_utils.py
+++ b/tests/test_kws_utils.py
@@ -1,7 +1,27 @@
 import re
 import unittest
 
-from funasr.utils.kws_utils import query_token_set, split_mixed_label, symbol_str
+import torch
+
+from funasr.utils.kws_utils import (
+    KwsCtcPrefixDecoder,
+    query_token_set,
+    split_mixed_label,
+    symbol_str,
+)
+
+
+class _IdentityCtc:
+    def softmax(self, x):
+        return x
+
+
+def _posteriors(token_ids, vocab_size=4):
+    # One frame per entry: token_id gets all the probability mass (0 is blank).
+    probs = torch.zeros(len(token_ids), vocab_size)
+    for frame, token_id in enumerate(token_ids):
+        probs[frame, token_id] = 1.0
+    return probs
 
 
 class KwsUtilsTest(unittest.TestCase):
@@ -18,6 +38,19 @@ def test_query_token_set_strips_symbols_before_character_lookup(self):
         self.assertEqual(tokens, ("a", "中"))
         self.assertEqual(token_ids, (1, 2))
 
+    def test_empty_keyword_entries_do_not_produce_detections(self):
+        token_list = ["<blank>", "<unk>", "小", "云"]
+        for keywords in ("小云小云,", "小云小云, ,", ",小云小云", "小云小云,!!"):
+            with self.subTest(keywords=keywords):
+                decoder = KwsCtcPrefixDecoder(_IdentityCtc(), keywords, token_list, {})
+
+                self.assertEqual(decoder.decode(_posteriors([0, 0, 0, 0])), (False, None, None))
+                self.assertEqual(decoder.decode(_posteriors([2, 0, 0, 0])), (False, None, None))
+                self.assertEqual(
+                    decoder.decode(_posteriors([2, 3, 0, 2, 3])), (True, "小云小云", 1.0)
+                )
+                self.assertEqual(list(decoder.keywords_token), ["小云小云"])
+
 
 if __name__ == "__main__":
     unittest.main()