Fixed a regression in the test suite where the test called
``CompareAndCopyTest::test_all_present`` would fail on some platforms due
to additional testing artifacts being detected. Pull request courtesy Nils
Philippsen.

In some circumstances, ephemeral class objects that are created within
the scope of a test method don't seem to be garbage collected directly
on exit. Filter out classes created in test modules.

Fixes: #7450
Closes: #7451
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7451
Pull-request-sha: 135a8aaba2c6941460c7f45aa1a55c8f6b9eb43d

Change-Id: I621967bd916089dc1e3f98625fd2a852cd9fd712

Corrected the error message for the ``AttributeError`` that's raised when
attempting to write to an attribute on the :class:`_result.Row` class,
which is immutable. The previous message claimed the column didn't exist
which is misleading.

Fixes: #7432
Change-Id: If0e2cbd3f763dca6c99a18aa42252c69f1207d59

This patch adds new warnings for all elements that
don't indicate their caching behavior, including user-defined
ClauseElement subclasses and third party dialects.
it additionally adds new documentation to discuss an apparent
performance degradation in 1.4 when caching is disabled as a
result in the significant expense incurred by ORM
lazy loaders, which in 1.3 used BakedQuery so were actually
cached.

As a result of adding the warnings, a fair degree of
lesser used SQL expression objects identified that they did not
define caching behavior so would have been producing
``[no key]``, including PostgreSQL constructs ``hstore``
and ``array``.  These have been amended to use inherit
cache where appropriate.  "on conflict" constructs in
PostgreSQL, MySQL, SQLite still explicitly don't generate
a cache key at this time.

The change also adds a test for all constructs via
assert_compile() to assert they will not generate cache
warnings.

Fixes: #7394
Change-Id: I85958affbb99bfad0f5efa21bc8f2a95e7e46981

Support multiple clause elements in the :meth:`_sql.Exists.where` method,
unifying the api with the on presented by a normal :func:`_sql.select`
construct.

Fixes: #7386
Change-Id: I5df20478008cd5167053d357cbfad8a641c62b44

Change-Id: I1ef2eb2018f4b68825fe40a2a8d99084cf217b35
References: #7257

this test was relying on gc to close out the connection.
this would lead to problems with aiosqlite as we invalidate
async connetions that aren't gracefully closed, and this test
suite was create tables per suite, so we'd get into a spot where
a new sqlite memory connection without the tables would get set up.

would only occur for full test run + -n2 + C extensions + python 3.7,
but we assume that is all related to just getting gc to trigger
or not trigger at exactly the right moment in this situation.

confirmed if we add a gc.collect() to the test without explcitly
closing out the conenction, the connection is gc'ed and detached,
and we get the error reproduced on the subsequent test.

Change-Id: Icc9d4bc703f0842c27600f532f34bc4c7d3baf21

Both sync and async versions are supported.

Fixes: #6842
Change-Id: I57751c5028acebfc6f9c43572562405453a2f2a4

Change-Id: I8172fdcc3103ff92aa049827728484c8779af6b7