Add validity to the inner elements of fixed-sized-lists

crates/re_types_builder/src/codegen/rust/serializer.rs

@@ -550,6 +550,34 @@ fn quote_arrow_field_serializer(
                 }
             };
 
+            // TODO(jleibs): The inner types of lists shouldn't be nullable, but both the python and
+            // C++ code-gen end up setting these to null when an outer fixed-sized field does happen
+            // to be null. In order to keep everything aligned at a validation level we match this
+            // behavior and create a validity-mask for the corresponding inner type. We can undo this if
+            // we make the C++ and Python codegen match the rust behavior or make our comparison tests
+            // more lenient.
+            let quoted_inner_bitmap =
+                if let DataType::FixedSizeList(_, count) = datatype.to_logical_type() {
+                    quote! {
+                        let #quoted_inner_bitmap: Option<::arrow2::bitmap::Bitmap>
+                            = #bitmap_src
+                                .as_ref()
+                                .map(|bitmap| {
+                                bitmap
+                                    .iter()
+                                    .map(|i| std::iter::repeat(i).take(#count))
+                                    .flatten()
+                                    .collect::<Vec<_>>()
+                                    .into()
+                                });
+                    }
+                } else {
+                    // TODO(cmc): We don't support intra-list nullability in our IDL at the moment.
+                    quote! {
+                        let #quoted_inner_bitmap: Option<::arrow2::bitmap::Bitmap> = None;
+                    }
+                };
+
             // TODO(cmc): We should be checking this, but right now we don't because we don't
             // support intra-list nullability.
             _ = is_nullable;
@@ -564,8 +592,7 @@ fn quote_arrow_field_serializer(
                     .map(Some)
                     .collect();
 
-                // TODO(cmc): We don't support intra-list nullability in our IDL at the moment.
-                let #quoted_inner_bitmap: Option<::arrow2::bitmap::Bitmap> = None;
+                #quoted_inner_bitmap
 
                 #quoted_create
             }}