Drop right-nested join rewriting

Dropped support for right-nested join rewriting to support old SQLite
versions prior to 3.7.16, released in 2013.   It is expected that
all modern Python versions among those now supported should all include
much newer versions of SQLite.

Fixes: #4895
Change-Id: I7f0cfc2b7d988ff147b9a4c6d5e2adec87e27029

2 files changed, 20 insertions, 37 deletions

diff --git a/lib/sqlalchemy/dialects/sqlite/base.py b/lib/sqlalchemy/dialects/sqlite/base.py
index defb64ec0..1bb7bd4fc 100644
--- a/lib/sqlalchemy/dialects/sqlite/base.py
+++ b/lib/sqlalchemy/dialects/sqlite/base.py
@@ -1467,9 +1467,15 @@ class SQLiteDialect(default.DefaultDialect):
         self.native_datetime = native_datetime
 
         if self.dbapi is not None:
-            self.supports_right_nested_joins = (
-                self.dbapi.sqlite_version_info >= (3, 7, 16)
-            )
+            if self.dbapi.sqlite_version_info < (3, 7, 16):
+                util.warn(
+                    "SQLite version %s is older than 3.7.16, and will not "
+                    "support right nested joins, as are sometimes used in "
+                    "more complex ORM scenarios.  SQLAlchemy 1.4 and above "
+                    "no longer tries to rewrite these joins."
+                    % (self.dbapi.sqlite_version_info,)
+                )
+
             self._broken_dotted_colnames = self.dbapi.sqlite_version_info < (
                 3,
                 10,
diff --git a/lib/sqlalchemy/dialects/sqlite/pysqlite.py b/lib/sqlalchemy/dialects/sqlite/pysqlite.py
index 4eca7ae31..89254eef1 100644
--- a/lib/sqlalchemy/dialects/sqlite/pysqlite.py
+++ b/lib/sqlalchemy/dialects/sqlite/pysqlite.py
@@ -18,19 +18,8 @@ r"""
 Driver
 ------
 
-When using Python 2.5 and above, the built in ``sqlite3`` driver is
-already installed and no additional installation is needed.  Otherwise,
-the ``pysqlite2`` driver needs to be present.  This is the same driver as
-``sqlite3``, just with a different name.
-
-The ``pysqlite2`` driver will be loaded first, and if not found, ``sqlite3``
-is loaded.  This allows an explicitly installed pysqlite driver to take
-precedence over the built in one.   As with all dialects, a specific
-DBAPI module may be provided to :func:`~sqlalchemy.create_engine()` to control
-this explicitly::
-
-    from sqlite3 import dbapi2 as sqlite
-    e = create_engine('sqlite+pysqlite:///file.db', module=sqlite)
+The ``sqlite3`` Python DBAPI is standard on all modern Python versions;
+for cPython and Pypy, no additional installation is necessary.
 
 
 Connect Strings
@@ -379,30 +368,18 @@ class SQLiteDialect_pysqlite(SQLiteDialect):
 
     driver = "pysqlite"
 
-    def __init__(self, uri=False, **kwargs):
-        SQLiteDialect.__init__(self, **kwargs)
-
-        if self.dbapi is not None:
-            sqlite_ver = self.dbapi.version_info
-            if sqlite_ver < (2, 1, 3):
-                util.warn(
-                    (
-                        "The installed version of pysqlite2 (%s) is out-dated "
-                        "and will cause errors in some cases.  Version 2.1.3 "
-                        "or greater is recommended."
-                    )
-                    % ".".join([str(subver) for subver in sqlite_ver])
-                )
-
     @classmethod
     def dbapi(cls):
-        try:
-            from pysqlite2 import dbapi2 as sqlite
-        except ImportError:
+        if util.py2k:
             try:
-                from sqlite3 import dbapi2 as sqlite  # try 2.5+ stdlib name.
-            except ImportError as e:
-                raise e
+                from pysqlite2 import dbapi2 as sqlite
+            except ImportError:
+                try:
+                    from sqlite3 import dbapi2 as sqlite
+                except ImportError as e:
+                    raise e
+        else:
+            from sqlite3 import dbapi2 as sqlite
         return sqlite
 
     @classmethod