scovich commented on code in PR #8324:
URL: https://github.com/apache/arrow-rs/pull/8324#discussion_r2342271492
##########
parquet-variant/src/builder.rs:
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@@ -709,6 +727,14 @@ pub enum ParentState<'a> {
saved_fields_size: usize,
finished: bool,
},
+ Custom {
+ value_builder: &'a mut ValueBuilder,
+ saved_value_builder_offset: usize,
+ metadata_builder: &'a mut dyn MetadataBuilder,
+ saved_metadata_builder_dict_size: usize,
+ state: Box<dyn CustomParentState + 'a>,
Review Comment:
Found the problems:
1. It wasn't safe for list and object parent state constructors to delegate
to the normal constructor, because they make eager changes (which happens
before invoking the delegated constructor and causes the wrong offsets to be
captured). Fixed by directly creating the parent state, instead of delegating
to the other constructor.
2. There was a subtle design flaw in the original
`CustomParentState::finish` -- it was overfitted to the `VariantArrayBuilder`
case, and called `metadata_builder.finish()` -- which no other builder wants to
do. FIxed by changing the signature to just pass the builders, instead of
finished offsets.
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