Fix ON TARGET DELETE ALLOW behavior when link optionality is changed (

#8419)

Currently, if you change whether a link is required, the behavior of
`ON TARGET DELETE ALLOW` isn't updated, so it might either incorrectly
allow or disallow deleting the last link, depending.

Fixes #8417.

edb/pgsql/delta.py

@@ -5278,6 +5278,17 @@ def apply(
                 self._alter_pointer_optionality(
                     schema, orig_schema, context, fill_expr=self.fill_expr)
 
+                # If the link has an Allow on target delete action, we
+                # need to refresh the triggers, since required and
+                # optional behave differently. (Required does a
+                # check.)
+                if (
+                    self.scls.get_on_target_delete(schema) ==
+                    s_links.LinkTargetDeleteAction.Allow
+                ):
+                    self.schedule_endpoint_delete_action_update(
+                        self.scls, orig_schema, schema, context)
+
         return schema
 
 

tests/test_edgeql_ddl.py

@@ -16259,6 +16259,46 @@ async def test_edgeql_ddl_link_policy_16(self):
             [],
         )
 
+    async def test_edgeql_ddl_link_policy_17(self):
+        # Make sure that ALLOW works when changing optionality
+        await self.con.execute(r"""
+            CREATE TYPE Tgt;
+            CREATE TYPE Src {
+                CREATE MULTI LINK tgt -> Tgt {
+                    ON TARGET DELETE ALLOW;
+                }
+            };
+        """)
+
+        await self.con.execute(r"""
+            INSERT Src { tgt := (INSERT Tgt) };
+        """)
+
+        await self.con.execute(r"""
+            ALTER TYPE Src {
+                ALTER LINK tgt {
+                    SET REQUIRED
+                }
+            };
+        """)
+
+        async with self.assertRaisesRegexTx(edgedb.MissingRequiredError, ''):
+            await self.con.execute("""
+                DELETE Tgt;
+            """)
+
+        await self.con.execute(r"""
+            ALTER TYPE Src {
+                ALTER LINK tgt {
+                    SET OPTIONAL
+                }
+            };
+        """)
+
+        await self.con.execute("""
+            DELETE Tgt;
+        """)
+
     async def test_edgeql_ddl_link_policy_implicit_01(self):
         await self.con.execute("""
             create type T;