fix: projected AwkwardInputLayers have __dask_tokenize__

src/dask_awkward/layers/layers.py

@@ -117,6 +117,19 @@ def io_func_implements_report(func: ImplementsIOFunction) -> bool:
     return hasattr(func, "return_report")
 
 
+class AwkwardTokenizable:
+
+    def __init__(self, ret_val, parent_name):
+        self.parent_name = parent_name
+        self.ret_val = ret_val
+
+    def __dask_tokenize__(self):
+        return ("AwkwardTokenizable", self.parent_name)
+
+    def __call__(self, *_, **__):
+        return self.ret_val
+
+
 class AwkwardInputLayer(AwkwardBlockwiseLayer):
     """A layer known to perform IO and produce Awkward arrays
 
@@ -230,7 +243,7 @@ def prepare_for_projection(self) -> tuple[AwkwardInputLayer, TypeTracerReport, T
         new_input_layer = AwkwardInputLayer(
             name=self.name,
             inputs=[None][: int(list(self.numblocks.values())[0][0])],
-            io_func=lambda *_, **__: new_return,
+            io_func=AwkwardTokenizable(new_return, self.name),
             label=self.label,
             produces_tasks=self.produces_tasks,
             creation_info=self.creation_info,

tests/test_inspect.py

@@ -97,6 +97,8 @@ def test_basic_root_works():
         .fill(events.MET_pt)
     )
 
+    columns = list(dak.necessary_columns(q1_hist).values())[0]
+    assert columns == frozenset({"MET_pt"})
     dask.compute(q1_hist)