[AMD] aiter: fail loudly on cross-layer KV sharing in target_verify (#38755)

test/srt/test_aiter_cross_layer_kv_guard.py

@@ -0,0 +1,45 @@
+"""PR2 guard: aiter target-verify rejects cross-layer KV sharing (k/v is None).
+
+Cross-layer KV sharing (Gemma4) passes ``k=v=None``. The legacy ragged
+``extend_attention_fwd`` target-verify path has no pool-reading fallback, so it
+must fail loudly with a ``ValueError`` naming the unified verify path rather
+than an opaque ``AttributeError`` on ``.contiguous``. The guard is inert when
+real K/V is passed.
+"""
+
+import unittest
+
+import torch
+
+from sglang.srt.layers.attention.aiter_backend import AiterAttnBackend
+from sglang.test.ci.ci_register import register_amd_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_amd_ci(est_time=10, suite="stage-b-test-1-gpu-small-amd-mi35x")
+
+
+class TestAiterCrossLayerKVGuard(CustomTestCase):
+    def test_raises_when_k_is_none(self):
+        with self.assertRaises(ValueError) as ctx:
+            AiterAttnBackend._reject_target_verify_cross_layer_kv(None, torch.empty(0))
+        self.assertIn("cross-layer KV", str(ctx.exception))
+        self.assertIn("unified verify path", str(ctx.exception))
+
+    def test_raises_when_v_is_none(self):
+        with self.assertRaises(ValueError):
+            AiterAttnBackend._reject_target_verify_cross_layer_kv(torch.empty(0), None)
+
+    def test_raises_when_both_none(self):
+        with self.assertRaises(ValueError):
+            AiterAttnBackend._reject_target_verify_cross_layer_kv(None, None)
+
+    def test_inert_when_kv_present(self):
+        # Real K/V present -> no raise (the guard must not fire for standard
+        # models that pass ragged K/V into the legacy target-verify path).
+        AiterAttnBackend._reject_target_verify_cross_layer_kv(
+            torch.empty(0), torch.empty(0)
+        )
+
+
+if __name__ == "__main__":
+    unittest.main()