Fixed error in union ffi. (#625)

.github/workflows/integration-ffi.yml

@@ -25,7 +25,7 @@ jobs:
           key: ${{ runner.os }}-amd64-target-maturin-cache
       - uses: actions/setup-python@v2
         with:
-          python-version: '3.7'
+          python-version: "3.7"
       - name: Install Python dependencies
         run: python -m pip install --upgrade pip setuptools wheel
       - name: Run tests
@@ -38,6 +38,6 @@ jobs:
           python -m venv venv
           source venv/bin/activate
 
-          pip install maturin==0.10.2 toml==0.10.1 pyarrow==5.0.0
+          pip install maturin==0.10.2 toml==0.10.1 pyarrow==6.0.0
           maturin develop
           python -m unittest discover tests

arrow-pyarrow-integration-testing/tests/test_sql.py

@@ -39,8 +39,7 @@ def tearDown(self):
         # No leak of C++ memory
         self.assertEqual(self.old_allocated_cpp, pyarrow.total_allocated_bytes())
 
-    # see https://issues.apache.org/jira/browse/ARROW-14680
-    def _test_null(self):
+    def test_null(self):
         """
         Python -> Rust -> Python
         """

src/array/union/ffi.rs

@@ -9,12 +9,11 @@ unsafe impl ToFfi for UnionArray {
     fn buffers(&self) -> Vec<Option<std::ptr::NonNull<u8>>> {
         if let Some(offsets) = &self.offsets {
             vec![
-                None,
                 Some(self.types.as_ptr().cast::<u8>()),
                 Some(offsets.as_ptr().cast::<u8>()),
             ]
         } else {
-            vec![None, Some(self.types.as_ptr().cast::<u8>())]
+            vec![Some(self.types.as_ptr().cast::<u8>())]
         }
     }
 
@@ -37,11 +36,11 @@ impl<A: ffi::ArrowArrayRef> FromFfi<A> for UnionArray {
         let data_type = field.data_type().clone();
         let fields = Self::get_fields(field.data_type());
 
-        let mut types = unsafe { array.buffer::<i8>(1) }?;
+        let mut types = unsafe { array.buffer::<i8>(0) }?;
         let offsets = if Self::is_sparse(&data_type) {
             None
         } else {
-            Some(unsafe { array.buffer::<i32>(2) }?)
+            Some(unsafe { array.buffer::<i32>(1) }?)
         };
 
         let length = array.array().len();