c-thiel commented on code in PR #2880:
URL: https://github.com/apache/iceberg-rust/pull/2880#discussion_r4446261961
##########
crates/iceberg/src/arrow/reader/projection.rs:
##########
@@ -237,6 +269,184 @@ impl ArrowReader {
}
}
+ /// Walks an Arrow `Fields` tree, recording `leaf_idx → variant_field_id`
for every
+ /// leaf that sits inside a variant column (top-level or nested in a
struct/list/map).
+ ///
+ /// The leaf numbering must match [`arrow_schema::Fields::filter_leaves`],
since the
+ /// resulting map is consulted by index in the `filter_leaves` passes
above. In
+ /// particular it mirrors `filter_leaves`' handling of
`Dictionary`/`RunEndEncoded`
+ /// (unwrapped to their value type) and `Union` (each member counted) —
otherwise a
+ /// mismatch would silently shift every variant leaf after it onto the
wrong column.
+ fn collect_variant_leaves(
+ fields: &Fields,
+ leaf_idx: &mut usize,
+ variant_parent: Option<i32>,
+ iceberg_schema: &Schema,
+ leaf_field_id_set: &HashSet<i32>,
+ out: &mut HashMap<usize, i32>,
+ ) -> Result<()> {
+ for field in fields {
+ Self::collect_variant_leaves_in_field(
+ field,
+ leaf_idx,
+ variant_parent,
+ iceberg_schema,
+ leaf_field_id_set,
+ out,
+ )?;
+ }
+ Ok(())
+ }
+
+ fn collect_variant_leaves_in_field(
+ field: &FieldRef,
+ leaf_idx: &mut usize,
+ variant_parent: Option<i32>,
+ iceberg_schema: &Schema,
+ leaf_field_id_set: &HashSet<i32>,
+ out: &mut HashMap<usize, i32>,
+ ) -> Result<()> {
+ // Once inside a variant, stay inside; otherwise check whether this
field is itself
+ // a variant column (its embedded field id resolves to
`Type::Variant`).
+ let entering_variant = variant_parent.is_none();
+ let effective_variant = variant_parent.or_else(|| {
+ Self::field_variant_id(field, iceberg_schema)
+ .filter(|fid| leaf_field_id_set.contains(fid))
+ });
+
+ // Reject shredded variants: a `typed_value` sub-field means the
payload is shredded,
+ // which we can't reconstruct yet. Projecting only metadata/value
would silently drop
+ // it, so fail loudly instead.
+ if entering_variant
+ && effective_variant.is_some()
+ && let DataType::Struct(sub) = field.data_type()
+ && sub.iter().any(|f| f.name() == "typed_value")
+ {
+ return Err(Error::new(
+ ErrorKind::FeatureUnsupported,
+ "Reading shredded variant columns is not supported yet: found
a `typed_value` \
+ sub-field. Only unshredded variants (metadata + value) can be
read.",
+ ));
+ }
+
+ // Mirror `Fields::filter_leaves`: unwrap `Dictionary`/`RunEndEncoded`
to their value
+ // type before deciding whether this is a leaf or a nested type to
descend into.
+ let data_type = match field.data_type() {
+ DataType::Dictionary(_, value) => value.as_ref(),
+ DataType::RunEndEncoded(_, value) => value.data_type(),
+ other => other,
+ };
+
+ match data_type {
+ DataType::Struct(sub) => {
+ Self::collect_variant_leaves(
+ sub,
+ leaf_idx,
+ effective_variant,
+ iceberg_schema,
+ leaf_field_id_set,
+ out,
+ )?;
+ }
+ DataType::List(inner)
+ | DataType::LargeList(inner)
+ | DataType::FixedSizeList(inner, _)
+ | DataType::Map(inner, _) => {
+ Self::collect_variant_leaves_in_field(
+ inner,
+ leaf_idx,
+ effective_variant,
+ iceberg_schema,
+ leaf_field_id_set,
+ out,
+ )?;
+ }
Review Comment:
Good call, done! The names are now `subfields` and `inner_field`, as you
suggested.
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