Make test_using_working_sst() easier to read by:
(1) replacing test_env::do_with() with seastar::async(),
seastar::defer(), and future::get();
(2) replacing seastar::async() and seastar::defer() with
test_env::do_with_async().
Technically speaking, this change does not perfectly preserve exceptional
behavior. Namely, test_env::do_with() uses future::finally() to link
test_env::stop() to the chain of futures, and future::finally() permits
test_env::stop() itself to throw an exception -- potentially leading to a
seastar::nested_exception being thrown, which would carry both the
original exception and the one thrown by test_env::stop().
Contrarily, the test_env::stop() deferred with seastar::defer() runs in a
destructor, and therefore test_env::stop() had better not throw there.
However, we will assume that test_env::stop() does not throw, albeit not
marked "noexcept". Prior commits 8d704f2532 ("sstable_test_env:
Coroutinize and move to .cc test_env::stop()", 2023-10-31) and
2c78b46c78 ("sstables::test_env: Carry compaction manager on board",
2023-10-31) show that we've considered individual actions in
test_env::stop() not to throw before.
The 128KB stack of seastar::thread (which underlies seastar::async())
should be a tolerable cost in a test case, in exchange for the improved
readability.
Signed-off-by: Laszlo Ersek <laszlo.ersek@scylladb.com>
79a8a6c638