GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/unexpand/bounded-memory is now passing!

Increasing lines. Very bad...

Increasing lines. Very bad...

I wouldn't worry too much about that as the increase is small ;-)

I think I duplicate many code about error handling when I try to support splice().
But I have no idea how to avoid it since

let mut aborted = None;
let mut errors = 0;

is not part of NamedWriter.

I'll reconsider this after #11466