Set DICTIONARY_ORDERED flag for FFI_ArrowSchema (#2050)

* Set DICTIONARY_ORDERED flag for FFI_ArrowSchema

* Fix clippy

arrow/src/datatypes/ffi.rs

@@ -288,12 +288,16 @@ impl TryFrom<&Field> for FFI_ArrowSchema {
     type Error = ArrowError;
 
     fn try_from(field: &Field) -> Result<Self> {
-        let flags = if field.is_nullable() {
+        let mut flags = if field.is_nullable() {
             Flags::NULLABLE
         } else {
             Flags::empty()
         };
 
+        if let Some(true) = field.dict_is_ordered() {
+            flags |= Flags::DICTIONARY_ORDERED;
+        }
+
         FFI_ArrowSchema::try_from(field.data_type())?
             .with_name(field.name())?
             .with_flags(flags)
@@ -435,4 +439,20 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn test_dictionary_ordered() -> Result<()> {
+        let schema = Schema::new(vec![Field::new_dict(
+            "dict",
+            DataType::Dictionary(Box::new(DataType::Int32), Box::new(DataType::Utf8)),
+            false,
+            0,
+            true,
+        )]);
+
+        let arrow_schema = FFI_ArrowSchema::try_from(schema)?;
+        assert!(arrow_schema.child(0).dictionary_ordered());
+
+        Ok(())
+    }
 }

arrow/src/ffi.rs

@@ -288,6 +288,10 @@ impl FFI_ArrowSchema {
     pub fn map_keys_sorted(&self) -> bool {
         self.flags & 0b00000100 != 0
     }
+
+    pub fn dictionary_ordered(&self) -> bool {
+        self.flags & 0b00000001 != 0
+    }
 }
 
 impl Drop for FFI_ArrowSchema {