Implement new ClauseElement role and coercion system

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

4 files changed, 9 insertions, 4 deletions

diff --git a/lib/sqlalchemy/testing/__init__.py b/lib/sqlalchemy/testing/__init__.py
index c52e9a76f..090c8488a 100644
--- a/lib/sqlalchemy/testing/__init__.py
+++ b/lib/sqlalchemy/testing/__init__.py
@@ -23,6 +23,7 @@ from .assertions import expect_warnings  # noqa
 from .assertions import in_  # noqa
 from .assertions import is_  # noqa
 from .assertions import is_false  # noqa
+from .assertions import is_instance_of  # noqa
 from .assertions import is_not_  # noqa
 from .assertions import is_true  # noqa
 from .assertions import le_  # noqa
diff --git a/lib/sqlalchemy/testing/assertions.py b/lib/sqlalchemy/testing/assertions.py
index d8038e225..819fedcc7 100644
--- a/lib/sqlalchemy/testing/assertions.py
+++ b/lib/sqlalchemy/testing/assertions.py
@@ -247,6 +247,10 @@ def le_(a, b, msg=None):
     assert a <= b, msg or "%r != %r" % (a, b)
 
 
+def is_instance_of(a, b, msg=None):
+    assert isinstance(a, b), msg or "%r is not an instance of %r" % (a, b)
+
+
 def is_true(a, msg=None):
     is_(a, True, msg=msg)
 
diff --git a/lib/sqlalchemy/testing/suite/test_cte.py b/lib/sqlalchemy/testing/suite/test_cte.py
index 012de7911..c7e6a266c 100644
--- a/lib/sqlalchemy/testing/suite/test_cte.py
+++ b/lib/sqlalchemy/testing/suite/test_cte.py
@@ -198,9 +198,9 @@ class CTETest(fixtures.TablesTest):
             conn.execute(
                 some_other_table.delete().where(
                     some_other_table.c.data
-                    == select([cte.c.data]).where(
-                        cte.c.id == some_other_table.c.id
-                    )
+                    == select([cte.c.data])
+                    .where(cte.c.id == some_other_table.c.id)
+                    .scalar_subquery()
                 )
             )
             eq_(
diff --git a/lib/sqlalchemy/testing/suite/test_results.py b/lib/sqlalchemy/testing/suite/test_results.py
index a07e45df2..8bf66d2eb 100644
--- a/lib/sqlalchemy/testing/suite/test_results.py
+++ b/lib/sqlalchemy/testing/suite/test_results.py
@@ -98,7 +98,7 @@ class RowFetchTest(fixtures.TablesTest):
 
         """
         datetable = self.tables.has_dates
-        s = select([datetable.alias("x").c.today]).as_scalar()
+        s = select([datetable.alias("x").c.today]).scalar_subquery()
         s2 = select([datetable.c.id, s.label("somelabel")])
         row = config.db.execute(s2).first()