From 6f9883b8b2ab1d3cb68e623e662be99fc5de68ad Mon Sep 17 00:00:00 2001
From: "Michael J. Sullivan" <sully@msully.net>
Date: Fri, 28 Feb 2025 11:45:54 -0800
Subject: [PATCH] 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       | 11 +++++++++++
 tests/test_edgeql_ddl.py | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/edb/pgsql/delta.py b/edb/pgsql/delta.py
index b447e6a4c07..82447d29499 100644
--- a/edb/pgsql/delta.py
+++ b/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
 
 
diff --git a/tests/test_edgeql_ddl.py b/tests/test_edgeql_ddl.py
index ceb26985f85..aedd5d56194 100644
--- a/tests/test_edgeql_ddl.py
+++ b/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;