ResultProxy won't autoclose connection until state flag is set

Changed the mechanics of :class:`.ResultProxy` to unconditionally
delay the "autoclose" step until the :class:`.Connection` is done
with the object; in the case where Postgresql ON CONFLICT with
RETURNING returns no rows, autoclose was occurring in this previously
non-existent use case, causing the usual autocommit behavior that
occurs unconditionally upon INSERT/UPDATE/DELETE to fail.

Change-Id: I235a25daf4381b31f523331f810ea04450349722
Fixes: #3955
(cherry picked from commit 8ee363e4917b0dcd64a83b6d26e465c9e61e0ea5)
(cherry picked from commit f52fb5282a046d26b6ee2778e03b995eb117c2ee)

3 files changed, 19 insertions, 12 deletions

diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index f680edada..91f4493c2 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -1203,14 +1203,22 @@ class Connection(Connectable):
         else:
             result = context.get_result_proxy()
             if result._metadata is None:
-                result._soft_close(_autoclose_connection=False)
+                result._soft_close()
 
         if context.should_autocommit and self._root.__transaction is None:
             self._root._commit_impl(autocommit=True)
 
-        if result._soft_closed and self.should_close_with_result:
-            self.close()
-
+        # for "connectionless" execution, we have to close this
+        # Connection after the statement is complete.
+        if self.should_close_with_result:
+            # ResultProxy already exhausted rows / has no rows.
+            # close us now
+            if result._soft_closed:
+                self.close()
+            else:
+                # ResultProxy will close this Connection when no more
+                # rows to fetch.
+                result._autoclose_connection = True
         return result
 
     def _cursor_execute(self, cursor, statement, parameters, context=None):
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 1c10f484f..628e23c9e 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -939,15 +939,15 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
                 row = result.fetchone()
                 self.returned_defaults = row
                 self._setup_ins_pk_from_implicit_returning(row)
-                result._soft_close(_autoclose_connection=False)
+                result._soft_close()
                 result._metadata = None
             elif not self._is_explicit_returning:
-                result._soft_close(_autoclose_connection=False)
+                result._soft_close()
                 result._metadata = None
         elif self.isupdate and self._is_implicit_returning:
             row = result.fetchone()
             self.returned_defaults = row
-            result._soft_close(_autoclose_connection=False)
+            result._soft_close()
             result._metadata = None
 
         elif result._metadata is None:
@@ -955,7 +955,7 @@ class DefaultExecutionContext(interfaces.ExecutionContext):
             # (which requires open cursor on some drivers
             # such as kintersbasdb, mxodbc)
             result.rowcount
-            result._soft_close(_autoclose_connection=False)
+            result._soft_close()
         return result
 
     def _setup_ins_pk_from_lastrowid(self):
diff --git a/lib/sqlalchemy/engine/result.py b/lib/sqlalchemy/engine/result.py
index 903b2c2f9..907dc7bd2 100644
--- a/lib/sqlalchemy/engine/result.py
+++ b/lib/sqlalchemy/engine/result.py
@@ -638,7 +638,7 @@ class ResultProxy(object):
 
     _process_row = RowProxy
     out_parameters = None
-    _can_close_connection = False
+    _autoclose_connection = False
     _metadata = None
     _soft_closed = False
     closed = False
@@ -792,7 +792,7 @@ class ResultProxy(object):
 
         return self._saved_cursor.description
 
-    def _soft_close(self, _autoclose_connection=True):
+    def _soft_close(self):
         """Soft close this :class:`.ResultProxy`.
 
         This releases all DBAPI cursor resources, but leaves the
@@ -820,8 +820,7 @@ class ResultProxy(object):
         self._soft_closed = True
         cursor = self.cursor
         self.connection._safe_close_cursor(cursor)
-        if _autoclose_connection and \
-                self.connection.should_close_with_result:
+        if self._autoclose_connection:
             self.connection.close()
         self.cursor = None