apacheGH-38553 : [C++] Replace null_count with MayHaveNulls in ListAr…

…rayFromArray and MapArray (apache#41957)

### Rationale for this change

Offsets could have `null_count() == -1` (`kUnknownNullCount`) meaning that offsets might contain nulls that are not accounted for which can produce failures (apache#38553) when working with `ListArray` or `MapArray`. `null_count()` should be replaced with `MayHaveNulls()`.

### What changes are included in this PR?

`null_count` is replaced with `MayHaveNulls` in `ListArrayFromArray`,  `MapArray::FromArraysInternal` and `MapArray::ValidateChildData`. Some tests had to be updated.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: apache#38553

Authored-by: AlenkaF <[email protected]>
Signed-off-by: Felipe Oliveira Carvalho <[email protected]>

cpp/src/arrow/array/array_list_test.cc

@@ -1383,7 +1383,7 @@ TEST_F(TestMapArray, FromArrays) {
 
   // Null bitmap and offset with offset
   ASSERT_RAISES(NotImplemented,
-                MapArray::FromArrays(offsets3->Slice(2), keys, items, pool_,
+                MapArray::FromArrays(offsets1->Slice(2), keys, items, pool_,
                                      offsets3->data()->buffers[0]));
 }
 

cpp/src/arrow/array/array_nested.cc

@@ -115,7 +115,7 @@ Result<std::shared_ptr<typename TypeTraits<TYPE>::ArrayType>> ListArrayFromArray
     return Status::TypeError("List offsets must be ", OffsetArrowType::type_name());
   }
 
-  if (null_bitmap != nullptr && offsets.null_count() > 0) {
+  if (null_bitmap != nullptr && offsets.data()->MayHaveNulls()) {
     return Status::Invalid(
         "Ambiguous to specify both validity map and offsets with nulls");
   }
@@ -827,7 +827,7 @@ Result<std::shared_ptr<Array>> MapArray::FromArraysInternal(
     return Status::Invalid("Map key and item arrays must be equal length");
   }
 
-  if (null_bitmap != nullptr && offsets->null_count() > 0) {
+  if (null_bitmap != nullptr && offsets->data()->MayHaveNulls()) {
     return Status::Invalid(
         "Ambiguous to specify both validity map and offsets with nulls");
   }
@@ -893,13 +893,13 @@ Status MapArray::ValidateChildData(
   if (pair_data->type->id() != Type::STRUCT) {
     return Status::Invalid("Map array child array should have struct type");
   }
-  if (pair_data->null_count != 0) {
+  if (pair_data->MayHaveNulls()) {
     return Status::Invalid("Map array child array should have no nulls");
   }
   if (pair_data->child_data.size() != 2) {
     return Status::Invalid("Map array child array should have two fields");
   }
-  if (pair_data->child_data[0]->null_count != 0) {
+  if (pair_data->child_data[0]->MayHaveNulls()) {
     return Status::Invalid("Map array keys array should have no nulls");
   }
   return Status::OK();

python/pyarrow/tests/test_array.py

@@ -1013,6 +1013,18 @@ def test_list_array_types_from_arrays_fail(list_array_type, list_type_factory):
             arr_slice.offsets, arr_slice.values, mask=arr_slice.is_null())
 
 
+def test_map_cast():
+    # GH-38553
+    t = pa.map_(pa.int64(), pa.int64())
+    arr = pa.array([{1: 2}], type=t)
+    result = arr.cast(pa.map_(pa.int32(), pa.int64()))
+
+    t_expected = pa.map_(pa.int32(), pa.int64())
+    expected = pa.array([{1: 2}], type=t_expected)
+
+    assert result.equals(expected)
+
+
 def test_map_labelled():
     #  ARROW-13735
     t = pa.map_(pa.field("name", "string", nullable=False), "int64")
@@ -1105,7 +1117,7 @@ def test_map_from_arrays():
 
     # error if null bitmap passed to sliced offset
     msg2 = 'Null bitmap with offsets slice not supported.'
-    offsets = pa.array(offsets, pa.int32())
+    offsets = pa.array([0, 2, 2, 6], pa.int32())
     with pytest.raises(pa.ArrowNotImplementedError, match=msg2):
         pa.MapArray.from_arrays(offsets.slice(2), keys, items, pa.map_(
             keys.type,