fuleinist opened a new pull request, #10515:
URL: https://github.com/apache/arrow-rs/pull/10515
## Summary
When converting an `FFI_ArrowSchema` (C Data Interface) into a `Field`, the
dictionary ordered flag is silently dropped.
`FFI_ArrowSchema::dictionary_ordered()`
reads the `ARROW_FLAG_DICTIONARY_ORDERED` bit (`0b1`) from
`ArrowSchema.flags`
correctly — but `impl TryFrom<&FFI_ArrowSchema> for Field` never applies it
to the
resulting `Field`.
As a result, a dictionary field exported with `dict_is_ordered = true`
always comes
back as `dict_is_ordered = false` after an FFI round trip.
## Fix
One-line change: call `.with_dict_is_ordered(c_schema.dictionary_ordered())`
when
constructing the `Field` in the `TryFrom<&FFI_ArrowSchema>` impl.
```rust
// Before
let mut field = Field::new(c_schema.name().unwrap_or(""), dtype,
c_schema.nullable());
// After
let mut field = Field::new(c_schema.name().unwrap_or(""), dtype,
c_schema.nullable())
.with_dict_is_ordered(c_schema.dictionary_ordered());
```
`with_dict_is_ordered` is a no-op on non-dictionary types, so this is safe
for all
schema types.
## Test
Adds `test_dictionary_ordered_roundtrip` that verifies both the ordered and
unordered paths survive an export/import round trip through the C Data
Interface.
Fixes #10513
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