Require equal chain lengths with ArviZ >=1

Due to API and behavior changes of `az.from_dict`,
it is no longer possible to pass lists of arrays.

Author: michaelosthege

.pylintrc

@@ -9,4 +9,5 @@ disable =
     R0912, # too many branches
     R0913, # too many arguments
     R0914, # too many local variables
+    R0915, # too many statements
     R1711, # useless return is okay

mcbackend/core.py

@@ -241,6 +241,11 @@ def to_inferencedata(self, *, equalize_chain_lengths: bool = True, **kwargs) ->
                     " and you should expect many ArviZ functions to choke on it."
                     "\nSpecify `to_inferencedata(equalize_chain_lengths=True)` to get regular inference data."
                 )
+                if _ARVIZ_VERSION > 0:
+                    raise NotImplementedError(
+                        "ArviZ 1.0 no longer supports uneven chain lengths."
+                        " See discussion in https://github.com/pymc-devs/mcbackend/pull/128."
+                    )
             else:
                 msg += "\nTruncating to the length of the shortest chain."
             _log.warning(msg)
@@ -288,7 +293,7 @@ def to_inferencedata(self, *, equalize_chain_lengths: bool = True, **kwargs) ->
         w_ss = cast(Dict[str, Union[Sequence, numpy.ndarray]], warmup_sample_stats)
         pst = cast(Dict[str, Union[Sequence, numpy.ndarray]], posterior)
         ss = cast(Dict[str, Union[Sequence, numpy.ndarray]], sample_stats)
-        if not equalize_chain_lengths:
+        if not equalize_chain_lengths or _ARVIZ_VERSION > 0:
             # Convert ragged arrays to object-dtyped ndarray because NumPy >=1.24.0 no longer does that automatically
             w_pst = {k: as_array_from_ragged(v) for k, v in warmup_posterior.items()}
             w_ss = {k: as_array_from_ragged(v) for k, v in warmup_sample_stats.items()}

mcbackend/test_backend_clickhouse.py

@@ -17,7 +17,7 @@
     column_spec_for,
     create_chain_table,
 )
-from mcbackend.core import Run, chain_id
+from mcbackend.core import _ARVIZ_VERSION, Run, chain_id
 from mcbackend.meta import ChainMeta, RunMeta, Variable
 from mcbackend.test_utils import CheckBehavior, CheckPerformance, make_runmeta
 
@@ -378,6 +378,11 @@ def test_to_inferencedata_equalize_chain_lengths(self, caplog):
         assert "Truncating to" in caplog.records[0].message
         assert len(idata_even.posterior.draw) == 14
 
+        if _ARVIZ_VERSION > 0:
+            with pytest.raises(NotImplementedError, match="ArviZ 1.0 no longer supports"):
+                run.to_inferencedata(equalize_chain_lengths=False)
+            return
+
         # With equalize=False the "draw" dim has the length of the longest chain (here: 8-3 = 5)
         caplog.clear()
         with caplog.at_level(logging.WARNING):