Applied an explicit "cause" to most if not all internally raised exceptions
that are raised from within an internal exception catch, to avoid
misleading stacktraces that suggest an error within the handling of an
exception.  While it would be preferable to suppress the internally caught
exception in the way that the ``__suppress_context__`` attribute would,
there does not as yet seem to be a way to do this without suppressing an
enclosing user constructed context, so for now it exposes the internally
caught exception as the cause so that full information about the context
of the error is maintained.

Fixes: #4849
Change-Id: I55a86b29023675d9e5e49bc7edc5a2dc0bcd4751

In 9fca5d827d we attempted to deprecate the "inline=True" flag
and add a generative inline() method, however failed to include
any tests and the method was implemented incorrectly such that
it would get overwritten with the boolean flag immediately.

Rename the internal "inline" flag to "_inline" and add test
support both for the method as well as deprecated support
for the flag, including a fixture addition to assert the expected
value of the flag as it generally does not affect the
actual compiled SQL string.

Change-Id: I0450049f17f1f0d91e22d27f1a973a2b6c0e59f7

The :meth:`.Connection.connect` method is deprecated as is the concept of
"connection branching", which copies a :class:`.Connection` into a new one
that has a no-op ".close()" method.  This pattern is oriented around the
"connectionless execution" concept which is also being removed in 2.0.

As part of this change we begin to move the internals away from
"connectionless execution" overall.   Remove the "connectionless
execution" concept from the reflection internals and replace with
explicit patterns at the Inspector level.

Fixes: #5131
Change-Id: Id23d28a9889212ac5ae7329b85136157815d3e6f

This collection was added only for the benefit of unit tests
and is unnecessary for the pool to function.  As SQLAlchemy 2.0
will be removing the automatic handling of connections that are
garbage collection, remove this collection so that we ultimately
don't need a weakref handler to do anything within the pool.
The handler will do nothing other than emit a warning that
a connection was dereferenced without being explicitly returned
to the pool, invalidated, or detached.

Change-Id: I4ca196270d5714efbac44dbf6f034e8c7f0af58a

Change-Id: I08440dc25e40ea1ccea1778f6ee9e28a00808235

The "expanding IN" feature, which generates IN expressions at query
execution time which are based on the particular parameters associated with
the statement execution, is now used for all IN expressions made against
lists of literal values.   This allows IN expressions to be fully cacheable
independently of the list of values being passed, and also includes support
for empty lists. For any scenario where the IN expression contains
non-literal SQL expressions, the old behavior of pre-rendering for each
position in the IN is maintained. The change also completes support for
expanding IN with tuples, where previously type-specific bind processors
weren't taking effect.

As part of this change, a more explicit separation between
"literal execute" and "post compile" bound parameters is being made;
as the "ansi bind rules" feature is rendering bound parameters
inline, as we now support "postcompile" generically, these should
be used here, however we have to render literal values at
execution time even for "expanding" parameters.  new test fixtures
etc. are added to assert everything goes to the right place.

Fixes: #4645
Change-Id: Iaa2b7bfbfaaf5b80799ee17c9b8507293cba6ed1

Fixed bug where parameter repr as used in logging and error reporting needs
additional context in order to distinguish between a list of parameters for
a single statement and a list of parameter lists, as the "list of lists"
structure could also indicate a single parameter list where the first
parameter itself is a list, such as for an array parameter.   The
engine/connection now passes in an additional boolean indicating how the
parameters should be considered.  The only SQLAlchemy backend that expects
arrays as parameters is that of  psycopg2 which uses pyformat parameters,
so this issue has not been too apparent, however as other drivers that use
positional gain more features it is important that this be supported. It
also eliminates the need for the parameter repr function to guess based on
the parameter structure passed.

Fixes: #4902
Change-Id: I086246ee0eb51484adbefd83e07295fa56576c5f

A major refactoring of all the functions handle all detection of
Core argument types as well as perform coercions into a new class hierarchy
based on "roles", each of which identify a syntactical location within a
SQL statement.  In contrast to the ClauseElement hierarchy that identifies
"what" each object is syntactically, the SQLRole hierarchy identifies
the "where does it go" of each object syntactically.   From this we define
a consistent type checking and coercion system that establishes well
defined behviors.

This is a breakout of the patch that is reorganizing select()
constructs to no longer be in the FromClause hierarchy.

Also includes a rename of as_scalar() into scalar_subquery(); deprecates
automatic coercion to scalar_subquery().

Partially-fixes: #4617
Change-Id: I26f1e78898693c6b99ef7ea2f4e7dfd0e8e1a1bd

Change-Id: I6a71f4924d046cf306961c58dffccf21e9c03911

Applied on top of a pure run of black -l 79 in
I7eda77fed3d8e73df84b3651fd6cfcfe858d4dc9,  this set of changes
resolves all remaining flake8 conditions for those codes
we have enabled in setup.cfg.

Included are resolutions for all remaining flake8 issues
including shadowed builtins, long lines, import order, unused
imports, duplicate imports, and docstring issues.

Change-Id: I4f72d3ba1380dd601610ff80b8fb06a2aff8b0fe