GenerationConfig validate both constraints and force_words_ids (#29163)

GenerationConfig validate both options for constrained decoding: constraints and force_words_ids

src/transformers/generation/configuration_utils.py

@@ -482,11 +482,11 @@ class GenerationConfig(PushToHubMixin):
         # 3. detect incorrect paramaterization specific to advanced beam modes
         else:
             # constrained beam search
-            if self.constraints is not None:
+            if self.constraints is not None or self.force_words_ids is not None:
                 constrained_wrong_parameter_msg = (
-                    "`constraints` is not `None`, triggering constrained beam search. However, `{flag_name}` is set "
-                    "to `{flag_value}`, which is incompatible with this generation mode. Set `constraints=None` or "
-                    "unset `{flag_name}` to continue." + fix_location
+                    "one of `constraints`, `force_words_ids` is not `None`, triggering constrained beam search. However, "
+                    "`{flag_name}` is set to `{flag_value}`, which is incompatible with this generation mode. Set "
+                    "`constraints` and `force_words_ids` to `None` or unset `{flag_name}` to continue." + fix_location
                 )
                 if self.do_sample is True:
                     raise ValueError(

tests/generation/test_configuration_utils.py

@@ -156,6 +156,11 @@ class GenerationConfigTest(unittest.TestCase):
         # Impossible sets of contraints/parameters will raise an exception
         with self.assertRaises(ValueError):
             GenerationConfig(do_sample=False, num_beams=1, num_return_sequences=2)
+        with self.assertRaises(ValueError):
+            # dummy constraint
+            GenerationConfig(do_sample=True, num_beams=2, constraints=["dummy"])
+        with self.assertRaises(ValueError):
+            GenerationConfig(do_sample=True, num_beams=2, force_words_ids=[[[1, 2, 3]]])
 
         # Passing `generate()`-only flags to `validate` will raise an exception
         with self.assertRaises(ValueError):