Generalize RETURNING and suppor for MariaDB / SQLite

As almost every dialect supports RETURNING now, RETURNING
is also made more of a default assumption.

* the default compiler generates a RETURNING clause now
  when specified; CompileError is no longer raised.
* The dialect-level implicit_returning parameter now has
  no effect.   It's not fully clear if there are real world
  cases relying on the dialect-level parameter, so we will see
  once 2.0 is released.   ORM-level RETURNING can be disabled
  at the table level, and perhaps "implicit returning" should
  become an ORM-level option at some point as that's where
  it applies.
* Altered ORM update() / delete() to respect table-level
  implicit returning for fetch.
* Since MariaDB doesnt support UPDATE returning, "full_returning"
  is now split into insert_returning, update_returning, delete_returning
* Crazy new thing.  Dialects that have *both* cursor.lastrowid
  *and* returning.   so now we can pick between them for SQLite
  and mariadb.  so, we are trying to keep it on .lastrowid for
  simple inserts with an autoincrement column, this helps with
  some edge case test scenarios and i bet .lastrowid is faster
  anyway.  any return_defaults() / multiparams etc then we
  use returning
* SQLite decided they dont want to return rows that match in
  ON CONFLICT.  this is flat out wrong, but for now we need to
  work with it.

Fixes: #6195
Fixes: #7011
Closes: #7047
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/7047
Pull-request-sha: d25d5ea3abe094f282c53c7dd87f5f53a9e85248

Co-authored-by: Mike Bayer <mike_mp@zzzcomputing.com>
Change-Id: I9908ce0ff7bdc50bd5b27722081767c31c19a950

1 files changed, 7 insertions, 13 deletions

diff --git a/lib/sqlalchemy/engine/create.py b/lib/sqlalchemy/engine/create.py
index 68a6b81e2..36119ab24 100644
--- a/lib/sqlalchemy/engine/create.py
+++ b/lib/sqlalchemy/engine/create.py
@@ -57,7 +57,7 @@ def create_engine(
     execution_options: _ExecuteOptions = ...,
     future: Literal[True],
     hide_parameters: bool = ...,
-    implicit_returning: bool = ...,
+    implicit_returning: Literal[True] = ...,
     isolation_level: _IsolationLevel = ...,
     json_deserializer: Callable[..., Any] = ...,
     json_serializer: Callable[..., Any] = ...,
@@ -266,18 +266,12 @@ def create_engine(url: Union[str, "_url.URL"], **kwargs: Any) -> Engine:
             :ref:`dbengine_logging` - further detail on how to configure
             logging.
 
-    :param implicit_returning=True:  Legacy flag that when set to ``False``
-        will disable the use of ``RETURNING`` on supporting backends where it
-        would normally be used to fetch newly generated primary key values for
-        single-row INSERT statements that do not otherwise specify a RETURNING
-        clause.  This behavior applies primarily to the PostgreSQL, Oracle,
-        SQL Server backends.
-
-        .. warning:: this flag originally allowed the "implicit returning"
-           feature to be *enabled* back when it was very new and there was not
-           well-established database support.  In modern SQLAlchemy, this flag
-           should **always be set to True**.  Some SQLAlchemy features will
-           fail to function properly if this flag is set to ``False``.
+    :param implicit_returning=True:  Legacy parameter that may only be set
+        to True. In SQLAlchemy 2.0, this parameter does nothing. In order to
+        disable "implicit returning" for statements invoked by the ORM,
+        configure this on a per-table basis using the
+        :paramref:`.Table.implicit_returning` parameter.
+
 
     :param isolation_level: optional string name of an isolation level
         which will be set on all new connections unconditionally.