fix(alias_table): walk parent groups iteratively and stop at the file root

src/legenddataflowscripts/utils/alias_table.py

@@ -7,46 +7,56 @@
 
 
 def convert_parents_to_structs(h5group):
-    """Recursively annotate HDF5 parent groups with LGDO ``struct`` datatype attributes.
+    """Annotate HDF5 parent groups with LGDO ``struct`` datatype attributes.
 
     When a new alias (hard link) is created inside an HDF5 file the parent
     groups may not carry the ``datatype`` attribute expected by the LGDO reader.
     This function walks up the HDF5 group hierarchy from *h5group* and ensures
     every ancestor group carries a ``datatype`` attribute of the form
     ``struct{child1,child2,…}``.
 
+    The root group is only updated if it already carries a ``datatype``; the
+    walk always stops there.
+
     Parameters
     ----------
     h5group : h5py.Group
         Leaf group whose parent hierarchy should be annotated.
     """
-    child = h5group.name.split("/")[-1]
-    if h5group.parent.name != "/" and len(h5group.parent.attrs) == 0:
-        h5group.parent.attrs.update({"datatype": "struct{" + child + "}"})
-    elif len(h5group.parent.attrs) > 0:
-        datatype = h5group.parent.attrs["datatype"]
-        if not (datatype.startswith("struct{") and datatype.endswith("}")):
-            msg = (
-                f"cannot register alias {child!r}: parent group "
-                f"{h5group.parent.name!r} has non-struct datatype {datatype!r}"
+    # the walk must be iterative: in h5py the root group is its own parent, so
+    # recursing on ``h5group.parent`` never terminates once ``/`` is reached
+    while h5group.name != "/":
+        parent = h5group.parent
+        child = h5group.name.rsplit("/", 1)[-1]
+
+        if "datatype" not in parent.attrs:
+            # never invent a datatype on the file root
+            if parent.name == "/":
+                return
+            parent.attrs.update({"datatype": "struct{" + child + "}"})
+        else:
+            datatype = parent.attrs["datatype"]
+            if not (datatype.startswith("struct{") and datatype.endswith("}")):
+                msg = (
+                    f"cannot register alias {child!r}: parent group "
+                    f"{parent.name!r} has non-struct datatype {datatype!r}"
+                )
+                raise ValueError(msg)
+            # membership must be tested against the parsed field list, not by
+            # substring (e.g. 'raw' is a substring of 'raw_blind')
+            fields = [
+                field.strip()
+                for field in datatype[len("struct{") : -1].split(",")
+                if field.strip()
+            ]
+            if child in fields:
+                # ancestors were annotated when this member was first added
+                return
+            parent.attrs.update(
+                {"datatype": "struct{" + ",".join([*fields, child]) + "}"}
             )
-            raise ValueError(msg)
-        # membership must be tested against the parsed field list, not by
-        # substring (e.g. 'raw' is a substring of 'raw_blind')
-        fields = [
-            field.strip()
-            for field in datatype[len("struct{") : -1].split(",")
-            if field.strip()
-        ]
-        if child in fields:
-            return
-        h5group.parent.attrs.update(
-            {"datatype": "struct{" + ",".join([*fields, child]) + "}"}
-        )
-    else:
-        return
-    convert_parents_to_structs(h5group.parent)
-    return
+
+        h5group = parent
 
 
 def alias_table(file: str | Path, mapping: str):

tests/test_utils_helpers.py

@@ -181,6 +181,34 @@ def test_alias_table_membership(tmp_path):
         assert f["det"].attrs["datatype"] == "struct{raw_blind,raw,raw2}"
 
 
+def test_alias_table_annotated_root(tmp_path):
+    """Aliasing into a new top-level group of a file whose root is a struct."""
+    lh5_file = tmp_path / "test.lh5"
+    with h5py.File(lh5_file, "w") as f:
+        for rawid, det in (("ch1027200", "V02160A"), ("ch1027201", "V02162B")):
+            grp = f.create_group(f"{rawid}/dsp")
+            grp.attrs["datatype"] = "table{a}"
+            grp.create_dataset("a", data=[1, 2, 3])
+            f[rawid].attrs["datatype"] = "struct{dsp}"
+        # real LH5 files always carry a datatype on the root group; the parent
+        # walk must stop there instead of recursing on it forever
+        f["/"].attrs["datatype"] = "struct{ch1027200,ch1027201}"
+
+    alias_table(lh5_file, {"ch1027200/dsp": "dsp/V02160A"})
+
+    with h5py.File(lh5_file) as f:
+        assert f["/"].attrs["datatype"] == "struct{ch1027200,ch1027201,dsp}"
+        assert f["dsp"].attrs["datatype"] == "struct{V02160A}"
+        assert list(f["dsp/V02160A/a"]) == [1, 2, 3]
+
+    # a second alias extends the new group but leaves the root untouched
+    alias_table(lh5_file, {"ch1027201/dsp": "dsp/V02162B"})
+
+    with h5py.File(lh5_file) as f:
+        assert f["/"].attrs["datatype"] == "struct{ch1027200,ch1027201,dsp}"
+        assert f["dsp"].attrs["datatype"] == "struct{V02160A,V02162B}"
+
+
 def test_build_log_excepthook(tmp_path, monkeypatch):
     monkeypatch.setattr(sys, "stderr", sys.stderr)
     monkeypatch.setattr(sys, "excepthook", sys.excepthook)