[IMP] create_m2m: auto generate and return table name

In order to limit chances for typos, while keeping the util backwards
compatible, allow users to provide the `util.AUTOMATIC` sentinel value to
automatically generate the m2m table name, following the same rule as the
ORM[^1].

The function now return the m2m table name.

[^1]: Example from 18.0
https://github.com/odoo/odoo/blob/f42fe80576c8b419b5215ff17859e0dfebcd996a/odoo/fields.py#L4918-L4923

Part-of: #304
Signed-off-by: Christophe Simonis (chs) <[email protected]>

Author: Pirols

src/base/tests/test_util.py

@@ -1045,6 +1045,18 @@ def test_ColumnList(self):
         self.assertTrue(s(ulc.using(alias="x")), ', "x"."a", "x"."A"')
         self.assertIs(ulc, ulc.using(leading_comma=True))
 
+    def test_create_m2m(self):
+        cr = self.env.cr
+
+        m2m_name = "random_table_name"
+        created_m2m = util.create_m2m(cr, m2m_name, "res_users", "res_groups")
+        self.assertEqual(m2m_name, created_m2m)
+        self.assertTrue(util.table_exists(cr, created_m2m))
+
+        auto_generated_m2m_table_name = util.create_m2m(cr, util.AUTO, "res_users", "res_groups")
+        self.assertEqual("res_groups_res_users_rel", auto_generated_m2m_table_name)
+        self.assertTrue(util.table_exists(cr, auto_generated_m2m_table_name))
+
 
 class TestORM(UnitTestCase):
     def test_create_cron(self):

src/util/pg.py

@@ -44,7 +44,7 @@
 
 from .exceptions import MigrationError, SleepyDeveloperError
 from .helpers import _validate_table, model_of_table
-from .misc import Sentinel, log_progress, on_CI, version_gte
+from .misc import AUTO, Sentinel, log_progress, on_CI, version_gte
 
 _logger = logging.getLogger(__name__)
 
@@ -1339,14 +1339,34 @@ def drop_depending_views(cr, table, column):
 
 
 def create_m2m(cr, m2m, fk1, fk2, col1=None, col2=None):
+    """
+    Ensure a m2m table exists or is created.
+
+    This function creates the table associated to a m2m field.
+    If the table already exists, :func:`~odoo.upgrade.util.pg.fixup_m2m` is run on it.
+    The table name can be generated automatically, applying the same logic of the ORM.
+    In order to do so, use the value "auto" for the `m2m` parameter.
+
+    :param str m2m: table name to create,
+                    if :const:`~odoo.upgrade.util.misc.AUTO` it is auto-generated
+    :param str fk1: first foreign key table name
+    :param str fk2: second foreign key table name
+    :param str col1: column referencing `fk1`, defaults to `"{fk1}_id"`
+    :param str col2: column referencing `fk2`, defaults to `"{fk2}_id"`
+    :return: the name of the table just created/fixed-up
+    :rtype: str
+    """
     if col1 is None:
         col1 = "%s_id" % fk1
     if col2 is None:
         col2 = "%s_id" % fk2
 
+    if m2m is AUTO:
+        m2m = "{}_{}_rel".format(*sorted([fk1, fk2]))
+
     if table_exists(cr, m2m):
         fixup_m2m(cr, m2m, fk1, fk2, col1, col2)
-        return
+        return m2m
 
     query = format_query(
         cr,
@@ -1366,6 +1386,8 @@ def create_m2m(cr, m2m, fk1, fk2, col1=None, col2=None):
     )
     cr.execute(query)
 
+    return m2m
+
 
 def update_m2m_tables(cr, old_table, new_table, ignored_m2ms=()):
     """