Deprecate connection branching

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

2 files changed, 36 insertions, 6 deletions

diff --git a/test/sql/test_defaults.py b/test/sql/test_defaults.py
index b31b070d8..2fded335b 100644
--- a/test/sql/test_defaults.py
+++ b/test/sql/test_defaults.py
@@ -163,12 +163,7 @@ class DefaultTest(fixtures.TestBase):
 
         def mydefault_using_connection(ctx):
             conn = ctx.connection
-            try:
-                return conn.execute(sa.select([sa.text("12")])).scalar()
-            finally:
-                # ensure a "close()" on this connection does nothing,
-                # since its a "branched" connection
-                conn.close()
+            return conn.execute(sa.select([sa.text("12")])).scalar()
 
         use_function_defaults = testing.against("postgresql", "mssql")
         is_oracle = testing.against("oracle")
diff --git a/test/sql/test_deprecations.py b/test/sql/test_deprecations.py
index b2b1f470b..b058cbe1b 100644
--- a/test/sql/test_deprecations.py
+++ b/test/sql/test_deprecations.py
@@ -1494,3 +1494,38 @@ class PositionalTextTest(fixtures.TablesTest):
             "Could not locate column in row for column 'text1.b'",
             lambda: row[text1.c.b],
         )
+
+
+class DefaultTest(fixtures.TestBase):
+    __backend__ = True
+
+    @testing.provide_metadata
+    def test_close_on_branched(self):
+        metadata = self.metadata
+
+        def mydefault_using_connection(ctx):
+            conn = ctx.connection
+            try:
+                return conn.execute(select([text("12")])).scalar()
+            finally:
+                # ensure a "close()" on this connection does nothing,
+                # since its a "branched" connection
+                conn.close()
+
+        table = Table(
+            "foo",
+            metadata,
+            Column("x", Integer),
+            Column("y", Integer, default=mydefault_using_connection),
+        )
+
+        metadata.create_all(testing.db)
+        with testing.db.connect() as conn:
+            with testing.expect_deprecated(
+                r"The .close\(\) method on a so-called 'branched' "
+                r"connection is deprecated as of 1.4, as are "
+                r"'branched' connections overall"
+            ):
+                conn.execute(table.insert().values(x=5))
+
+            eq_(conn.execute(select([table])).first(), (5, 12))