[C++] Can't concatenate extension arrays

[asfimport]

It looks like Arrays with an extension type can't be concatenated. From the R bindings:

library(arrow, warn.conflicts = FALSE)

arr <- vctrs_extension_array(1:10)
concat_arrays(arr, arr)
#> Error: NotImplemented: concatenation of integer(0)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:195  VisitTypeInline(*out_->type, this)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:590  ConcatenateImpl(data, pool).Concatenate(&out_data)

This shows up more practically when using the query engine:

library(arrow, warn.conflicts = FALSE)

table <- arrow_table(
  group = rep(c("a", "b"), 5),
  col1 = 1:10,
  col2 = vctrs_extension_array(1:10)
)

tf <- tempfile()
table |> dplyr::group_by(group) |> write_dataset(tf)
open_dataset(tf) |>
  dplyr::arrange(col1) |> 
  dplyr::collect()
#> Error in `dplyr::collect()`:
#> ! NotImplemented: concatenation of extension<arrow.r.vctrs>
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:195  VisitTypeInline(*out_->type, this)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/array/concatenate.cc:590  ConcatenateImpl(data, pool).Concatenate(&out_data)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/kernels/vector_selection.cc:2025  Concatenate(values.chunks(), ctx->memory_pool())
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/kernels/vector_selection.cc:2084  TakeCA(*table.column(j), indices, options, ctx)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/exec/sink_node.cc:527  impl_->DoFinish()
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/compute/exec/exec_plan.cc:467  iterator_.Next()
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/record_batch.cc:337  ReadNext(&batch)
#> /Users/deweydunnington/Desktop/rscratch/arrow/cpp/src/arrow/record_batch.cc:351  ToRecordBatches()

Reporter: Dewey Dunnington / @paleolimbot
Assignee: Joris Van den Bossche / @jorisvandenbossche

Related issues:

• [C++][Python] Cannot concatenate extension arrays (duplicates)

PRs and other links:

• GitHub Pull Request #14463

_{Note: This issue was originally created as ARROW-16503. Please see the migration documentation for further details.}