[C++] REEBuilder Produces Incorrect Values When Using AppendArraySlice

[andishgar]

Describe the bug, including details regarding any error messages, version, and platform.

The following code:

auto run_end_builder = std::make_shared<Int32Builder>();
auto value_builder = std::make_shared<FloatBuilder>();
auto run_end_encoded_type = run_end_encoded(int32(), float32());
RunEndEncodedBuilder builder(default_memory_pool(), run_end_builder,
                             value_builder, run_end_encoded_type);

ASSERT_OK(builder.AppendScalar(**MakeScalar(float32(), 2), 3));
ASSERT_OK_AND_ASSIGN(auto array_1, builder.Finish());

ASSERT_OK(builder.AppendScalar(**MakeScalar(float32(), 2), 3));
ArraySpan span(*array_1->data());
ASSERT_OK(builder.AppendArraySlice(span, 0, 3));

ASSERT_OK_AND_ASSIGN(auto array_2, builder.Finish());
ARROW_LOGGER_INFO("", array_2->ToString());

produces the following output. This indicates that the run from the appended array is not merged with the existing open run in the builder, even though both runs contain the same value.

-- run_ends:
  [
    3,
    6
  ]
-- values:
  [
    2,
    2
  ]

Component(s)

C++

[andishgar]

@pitrou, would you consider this expected behavior, or is it a bug?