fix(sampling): reject non-finite temperature in SamplingParams.verify (#28153)

Signed-off-by: Ting Sun <suntcrick@gmail.com>

python/sglang/srt/sampling/sampling_params.py

@@ -14,6 +14,7 @@
 """Sampling parameters for text generation."""
 
 import logging
+import math
 from typing import Any, Dict, List, Optional, Union
 
 # sre_parse is deprecated in Python 3.11+, use re._parser instead
@@ -118,9 +119,9 @@ class SamplingParams:
             self.top_k = TOP_K_ALL  # whole vocabulary
 
     def verify(self, vocab_size):
-        if self.temperature < 0.0:
+        if not math.isfinite(self.temperature) or self.temperature < 0.0:
             raise ValueError(
-                f"temperature must be non-negative, got {self.temperature}."
+                f"temperature must be a non-negative finite number, got {self.temperature}."
             )
         if not 0.0 < self.top_p <= 1.0:
             raise ValueError(f"top_p must be in (0, 1], got {self.top_p}.")

test/registered/unit/sampling/test_sampling_params.py

@@ -92,6 +92,18 @@ class TestSamplingParamsVerify(CustomTestCase):
         with self.assertRaises(ValueError):
             sp.verify(self.VOCAB_SIZE)
 
+    def test_nan_temperature_raises(self):
+        """verify() must reject NaN temperature; the bare < 0.0 check alone lets it through."""
+        sp = self._make(temperature=float("nan"))
+        with self.assertRaises(ValueError):
+            sp.verify(self.VOCAB_SIZE)
+
+    def test_inf_temperature_raises(self):
+        """verify() must reject non-finite (inf) temperature."""
+        sp = self._make(temperature=float("inf"))
+        with self.assertRaises(ValueError):
+            sp.verify(self.VOCAB_SIZE)
+
     # --- top_p ---
     def test_top_p_negative_raises(self):
         """Test that verify() rejects negative top_p (valid range is (0, 1])."""