wgtmac commented on PR #43995:
URL: https://github.com/apache/arrow/pull/43995#issuecomment-2336585735
```
optional group a (LIST) {
repeated group array (LIST) {
repeated int32 array;
}
}
```
IMO, the root cause is that the current code recognizes the schema above as
a three-level encoding. However, the inner-most field can only be `required` or
`optional` in three-level encoding, but here the int32 field is `repeated`. We
can decouple the nesting field into two lists as below:
```
outer_list:
optional group a (LIST) {
repeated group array (LIST) {}
}
inner_list:
repeated group array (LIST) {
repeated int32 array;
}
```
It is obvious that `inner_list` can simply apply backward-compatibility rule
(1). For the `outer_list`, the current code applies rule (3). I think we need
to apply rule (4) here by modifying the rule (3) to below:
> If the repeated field is a group with one **required or optional** field
and is named either array or uses the LIST-annotated group's name with _tuple
appended then the repeated type is the element type and elements are required.
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