Use importlib_metadata; add namespace for mariadb

The ``importlib_metadata`` library is used to scan for setuptools
entrypoints rather than pkg_resources.   as importlib_metadata is a small
library that is included as of Python 3.8, the compatibility library is
installed as a dependency for Python versions older than 3.8.

Unfortunately setuptools "attr:" is broken because it tries to import
the module; seems like this is fixed as part of
https://github.com/pypa/setuptools/pull/1753 however this is too recent
to rely upon for now.

Added a new dialect token "mariadb" that may be used in place of "mysql" in
the :func:`_sa.create_engine` URL.  This will deliver a MariaDB dialect
subclass of the MySQLDialect in use that forces the "is_mariadb" flag to
True.  The dialect will raise an error if a server version string that does
not indicate MariaDB in use is received.   This is useful for
MariaDB-specific testing scenarios as well as to support applications that
are hardcoding to MariaDB-only concepts.  As MariaDB and MySQL featuresets
and usage patterns continue to diverge, this pattern may become more
prominent.

Fixes: #5400
Fixes: #5496
Change-Id: I330815ebe572b6a9818377da56621397335fa702

1 files changed, 3 insertions, 7 deletions

diff --git a/test/dialect/mysql/test_compiler.py b/test/dialect/mysql/test_compiler.py
index 09bdd80be..2053318b6 100644
--- a/test/dialect/mysql/test_compiler.py
+++ b/test/dialect/mysql/test_compiler.py
@@ -150,13 +150,11 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
         constraint_name = "constraint"
         constraint = CheckConstraint("data IS NOT NULL", name=constraint_name)
         Table(table_name, m, Column("data", String(255)), constraint)
-        dialect = mysql.dialect()
-        dialect.server_version_info = (10, 1, 1, "MariaDB")
         self.assert_compile(
             schema.DropConstraint(constraint),
             "ALTER TABLE %s DROP CONSTRAINT `%s`"
             % (table_name, constraint_name),
-            dialect=dialect,
+            dialect="mariadb",
         )
 
     def test_create_index_with_length_quoted(self):
@@ -354,8 +352,6 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
         self.assert_compile(expr, "concat('x', 'y')", literal_binds=True)
 
     def test_mariadb_for_update(self):
-        dialect = mysql.dialect()
-        dialect.server_version_info = (10, 1, 1, "MariaDB")
 
         table1 = table(
             "mytable", column("myid"), column("name"), column("description")
@@ -366,7 +362,7 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
             "FOR UPDATE",
-            dialect=dialect,
+            dialect="mariadb",
         )
 
         self.assert_compile(
@@ -376,7 +372,7 @@ class CompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
             "FOR UPDATE",
-            dialect=dialect,
+            dialect="mariadb",
         )
 
     def test_delete_extra_froms(self):