Check for maximum value for layout in views (#308)

* Check for maximum value for layout in views

* Work with nested layout like [[0], [1, 2, 3], [4]]

* Only check for integers

* Added unit test

* Update lumen/target.py

Co-authored-by: Philipp Rudiger <prudiger@anaconda.com>

Co-authored-by: Philipp Rudiger <prudiger@anaconda.com>

lumen/target.py

@@ -51,11 +51,18 @@ def __panel__(self):
     def _construct_layout(self):
         layout = self.layout
         if isinstance(layout, list):
+            view_size = len(self.views)
             item = pn.Column(sizing_mode='stretch_both')
             for row_spec in layout:
                 row = pn.Row(sizing_mode='stretch_width')
                 for index in row_spec:
                     if isinstance(index, int):
+                        if index >= view_size:
+                            raise ValueError(
+                                f"Layout specification for '{self.title}' target references "
+                                f"out-of-bounds index ({index}) even though the maximum "
+                                f"available index is {view_size - 1}."
+                            )
                         view = self.views[index]
                     else:
                         matches = [view for view in self.views if view.name == index]

lumen/tests/test_target.py

@@ -2,6 +2,7 @@
 
 import holoviews as hv
 import numpy as np
+import pytest
 
 from bokeh.document import Document
 from panel.io.server import set_curdoc
@@ -182,3 +183,40 @@ def test_transform_controls_facetted(set_root):
 
         assert np.array_equal(hv_pane1.object['A'], np.array([4, 2, 0]))
         assert np.array_equal(hv_pane2.object['A'], np.array([3, 1]))
+
+
+@pytest.mark.parametrize(
+    "layout,error",
+    [
+        ([[0]], None),
+        ([[0], [1]], ValueError),
+        ([[0], [1, 2]], ValueError),
+        ([{"test": 0}], None),
+        ([{"test1": 0}], KeyError),
+    ]
+)
+def test_layout_view(set_root, layout, error):
+    set_root(str(Path(__file__).parent))
+    source = FileSource(tables={'test': 'sources/test.csv'})
+    derived = DerivedSource(source=source, transforms=[Astype(dtypes={'B': 'int'})])
+    views = {
+        'test': {
+            'type': 'table',
+            'table': 'test',
+        },
+    }
+    spec = {
+        'source': 'test',
+        'views': views,
+        'layout': layout
+    }
+
+    doc = Document()
+    with set_curdoc(doc):
+        state.sources['test'] = derived
+
+        if error is not None:
+            with pytest.raises(error):
+                Target.from_spec(spec, sources={'test': derived})
+        else:
+            Target.from_spec(spec, sources={'test': derived})