Fix exception when loading NXdata with NXlog signal

docs/about/release-notes.rst

@@ -28,6 +28,17 @@ Release Notes
    Neil Vaytet :sup:`a`\ ,
    and Jan-Lukas Wynen :sup:`a`
 
+v23.04.0
+--------
+
+Features
+~~~~~~~~
+
+* Added the future API of ``scippnexus`` as ``scippnexus.v2``.
+  For many users the API changes will be minor.
+  The old API will be deprecated soon and users should try to migrate to the new API.
+  Note that ``v2`` is not fully stable yet and in particular the behavior in edge cases is subject to change.
+
 v23.03.0
 --------
 

docs/index.rst

@@ -27,6 +27,11 @@ This is especially powerful since a number of concepts of Scipp map well to conc
 News
 ----
 
+- [April 2023] scippnexus-23.04.0 has been released.
+  This adds ``scippnexus.v2``, which provides the future API of ``scippnexus``.
+  The new API avoids performance bottlenecks when working with small files that contain many groups and datasets.
+  The new behavior is also more faithful to the file content.
+  ``v2`` will become the default in the near future.
 - [March 2023] scippnexus-23.03.0 has been released.
   This brings a number of improvements, including handling of legacy files and loading of geometry information.
 - [January 2023] scippnexus-23.01.0 has been released.

src/scippnexus/v2/nxdata.py

@@ -89,6 +89,14 @@ def __init__(self,
                     self._valid = False
 
     def _init_signal(self, name: Optional[str], children):
+        # There are multiple ways NeXus can define the "signal" dataset. The latest
+        # version uses `signal` attribute on the group (passed as `name`). However,
+        # we must give precedence to the `signal` attribute on the dataset, since
+        # older files may use that (and the `signal` group attribute is unrelated).
+        # Finally, NXlog and NXevent_data can take the role of the signal. In practice
+        # those may not be indicate by a `signal` attribute, but we support that
+        # anyway since otherwise we would not be able to find NXevent_data signals
+        # in many common files.
         if name is not None and name in children:
             self._signal_name = name
             self._signal = children[name]
@@ -102,6 +110,9 @@ def _init_signal(self, name: Optional[str], children):
                 break
         # NXlog or NXevent_data can take the role of the signal.
         for name, field in children.items():
+            if name == self._signal_name:
+                # Avoid duplicate handling
+                continue
             if isinstance(field,
                           EventField) or (isinstance(field, Group)
                                           and field.nx_class in [NXlog, NXevent_data]):

tests/nxdata_test.py

@@ -211,6 +211,23 @@ def test_auxiliary_signal_causes_load_as_dataset(h5root):
     assert_identical(data[...], sc.Dataset({'signal': da.data, 'xx': da.coords['xx']}))
 
 
+def test_NXlog_data_is_loaded_as_time_dependent_data_array(nxroot):
+    da = sc.DataArray(data=sc.array(dims=['time'], unit='K', values=[1, 2, 3]),
+                      coords={
+                          'time':
+                          sc.epoch(unit='s') +
+                          sc.array(dims=['time'], unit='s', values=[1, 2, 3])
+                      })
+    data = nxroot.create_class('data1', NXdata)
+    log = data.create_class('data', NXlog)
+    log['time'] = da.coords['time']
+    log['value'] = da.data
+    data._group.attrs['signal'] = 'data'
+
+    loaded = data[()]
+    assert_identical(loaded, da)
+
+
 def test_field_dims_match_NXdata_dims(h5root):
     da = sc.DataArray(
         sc.array(dims=['xx', 'yy'], unit='m', values=[[1, 2, 3], [4, 5, 6]]))