[C++] Allow automatic String -> LargeString promotions when concatenating tables

[asfimport]

inspired by GitHub issue #5874

Reporter: Wes McKinney / @wesm

Related issues:

• [C++] C++ array kernels framework and execution buildout (umbrella issue) (is a child of)
• [C++][Python] Large strings cause ArrowInvalid: offset overflow while concatenating arrays (is related to)
• [Python] combine_chunks fails on column of table, but does not error on table itself (is related to)

_{Note: This issue was originally created as ARROW-7245. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
Perhaps Concatenate can be reimplemented as a vector kernel, so that type promotions can be handled by the kernel execution machinery

[asfimport]

Clark Zinzow:
+1 to having Concatenate go through the type promotion logic in the compute layer. I'm currently running into a similar issue with concatenating tables with different numeric types that can certainly be promoted to a common numeric type. I'm currently working around this in application code by doing manual type promotion of each column to the common dtype for that column across all tables (mimicking Arrow's internal type promotion logic here)) before concatenating the tables.

Here is a pyarrow MWE:

In [1]: t1 = pa.table({"a": pa.array([1, 2], type=pa.int16())})

In [2]: t2 = pa.table({"a": pa.array([3, 4], type=pa.int64())})

In [3]: pa.concat_tables([t1, t2])
---------------------------------------------------------------------------
ArrowInvalid                              Traceback (most recent call last)
<ipython-input-91-40afec1155a5> in <module>
----> 1 pa.concat_tables([t1, t2])

~/.local/lib/python3.7/site-packages/pyarrow/table.pxi in pyarrow.lib.concat_tables()

~/.local/lib/python3.7/site-packages/pyarrow/error.pxi in pyarrow.lib.pyarrow_internal_check_status()

~/.local/lib/python3.7/site-packages/pyarrow/error.pxi in pyarrow.lib.check_status()

ArrowInvalid: Schema at index 1 was different:
a: int16
vs
a: int64