[Bugfix][Diffusion] Honor HF_HUB_OFFLINE in OmniDiffusionConfig (align with AR stage) (#5403)

Signed-off-by: Weiming Liao <liaowm5@gmail.com>
Signed-off-by: Weiming Liao <fayespica@outlook.com>
Co-authored-by: 汪志鹏 <wangzhipeng628@gmail.com>

tests/diffusion/test_omni_diffusion_config_offline_model_path.py

@@ -0,0 +1,60 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Unit tests for OmniDiffusionConfig HF-offline model-path resolution."""
+
+import os
+
+import huggingface_hub
+import pytest
+
+import vllm_omni.diffusion.data as diffusion_data
+from vllm_omni.diffusion.data import OmniDiffusionConfig
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+_LOCAL_SNAPSHOT = "/root/.cache/huggingface/hub/models--foo--bar/snapshots/deadbeef"
+
+
+@pytest.fixture
+def record_get_model_path(monkeypatch: pytest.MonkeyPatch):
+    calls: list[tuple[str, str | None]] = []
+
+    def fake_get_model_path(model, revision=None):
+        calls.append((model, revision))
+        if os.path.exists(model):
+            return model
+        return _LOCAL_SNAPSHOT
+
+    monkeypatch.setattr(diffusion_data, "get_model_path", fake_get_model_path)
+    return calls
+
+
+class TestOmniDiffusionConfigOfflineModelPath:
+    def test_offline_repo_id_replaced_with_local_path(
+        self, monkeypatch: pytest.MonkeyPatch, record_get_model_path
+    ) -> None:
+        monkeypatch.setattr(huggingface_hub.constants, "HF_HUB_OFFLINE", True)
+        config = OmniDiffusionConfig(model="foo/bar")
+        assert config.model == _LOCAL_SNAPSHOT
+        assert record_get_model_path == [("foo/bar", None)]
+
+    def test_online_leaves_model_untouched(self, monkeypatch: pytest.MonkeyPatch, record_get_model_path) -> None:
+        monkeypatch.setattr(huggingface_hub.constants, "HF_HUB_OFFLINE", False)
+        config = OmniDiffusionConfig(model="foo/bar")
+        assert config.model == "foo/bar"
+        assert record_get_model_path == []
+
+    def test_offline_local_path_unchanged(self, monkeypatch: pytest.MonkeyPatch, tmp_path) -> None:
+        monkeypatch.setattr(huggingface_hub.constants, "HF_HUB_OFFLINE", True)
+        local = str(tmp_path)
+        config = OmniDiffusionConfig(model=local)
+        assert config.model == local
+
+    @pytest.mark.parametrize("model", [None, ""])
+    def test_offline_empty_model_unchanged(
+        self, monkeypatch: pytest.MonkeyPatch, record_get_model_path, model: str | None
+    ) -> None:
+        monkeypatch.setattr(huggingface_hub.constants, "HF_HUB_OFFLINE", True)
+        config = OmniDiffusionConfig(model=model)
+        assert config.model == model
+        assert record_get_model_path == []