[GraphBolt] add available builtin datasets into docstring (#6346)

python/dgl/graphbolt/impl/ondisk_dataset.py

@@ -482,6 +482,29 @@ class BuiltinDataset(OnDiskDataset):
     This class is used to help download datasets from DGL S3 storage and load
     them as ``OnDiskDataset``.
 
+    Available builtin datasets include:
+    **ogbn-mag**
+        The ogbn-mag dataset is a heterogeneous network composed of a subset of
+        the Microsoft Academic Graph (MAG). See more details in
+        `ogbn-mag <https://ogb.stanford.edu/docs/nodeprop/#ogbn-mag>`_.
+        .. note::
+            Reverse edges are added to the original graph and duplicated
+            edges are removed.
+
+    **ogbl-citation2**
+        The ogbl-citation2 dataset is a directed graph, representing the
+        citation network between a subset of papers extracted from MAG. See
+        more details in `ogbl-citation2
+        <https://ogb.stanford.edu/docs/linkprop/#ogbl-citation2>`_.
+
+    **ogbn-products**
+        The ogbn-products dataset is an undirected and unweighted graph,
+        representing an Amazon product co-purchasing network. See more details
+        in `ogbn-products
+        https://ogb.stanford.edu/docs/nodeprop/#ogbn-products>`_.
+        .. note::
+            Reverse edges are added to the original graph.
+
     Parameters
     ----------
     name : str
@@ -491,10 +514,16 @@ class BuiltinDataset(OnDiskDataset):
     """
 
     _base_url = "https://data.dgl.ai/dataset/graphbolt/"
+    _datasets = ["ogbn-mag", "ogbl-citation2", "ogbn-products"]
 
     def __init__(self, name: str, root: str = "datasets") -> OnDiskDataset:
         dataset_dir = os.path.join(root, name)
         if not os.path.exists(dataset_dir):
+            if name not in self._datasets:
+                raise RuntimeError(
+                    f"Dataset {name} is not available. Available datasets are "
+                    f"{self._datasets}."
+                )
             url = self._base_url + name + ".zip"
             os.makedirs(root, exist_ok=True)
             zip_file_path = os.path.join(root, name + ".zip")

tests/python/pytorch/graphbolt/impl/test_ondisk_dataset.py

@@ -1701,6 +1701,8 @@ def test_BuiltinDataset():
     with tempfile.TemporaryDirectory() as test_dir:
         # Case 1: download from DGL S3 storage.
         dataset_name = "test-only"
+        # Add test-only dataset to the builtin dataset list for testing only.
+        gb.BuiltinDataset._datasets.append(dataset_name)
         dataset = gb.BuiltinDataset(name=dataset_name, root=test_dir).load()
         assert dataset.graph is not None
         assert dataset.feature is not None
@@ -1713,3 +1715,11 @@ def test_BuiltinDataset():
         assert dataset.feature is not None
         assert dataset.tasks is not None
         assert dataset.dataset_name == dataset_name
+
+        # Case 3: dataset is not available.
+        dataset_name = "fake_name"
+        with pytest.raises(
+            RuntimeError,
+            match=rf"Dataset {dataset_name} is not available.*",
+        ):
+            _ = gb.BuiltinDataset(name=dataset_name, root=test_dir).load()