refactor(postgres): address Greptile review on warranty_claim on_cancel

- Filter the parent Maintenance Visit's docstatus (mv.docstatus != 2) via a qb join, as
  the original SQL did, instead of the child Maintenance Visit Purpose row's docstatus.
  Synced in normal flows, but exactly faithful to the original intent.
- Add a limit(500) to bound the read on a cancellation path.

Adds two both-engine tests calling on_cancel directly: an active (non-cancelled) visit
blocks the claim cancel; with no referencing visit the claim is marked Cancelled.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

erpnext/support/doctype/warranty_claim/test_warranty_claim.py

@@ -84,3 +84,20 @@ class TestWarrantyClaim(ERPNextTestSuite):
 		self.assertIsNotNone(target)
 		self.assertTrue(target.is_new())
 		self.assertEqual(target.doctype, "Maintenance Visit")
+
+	def test_on_cancel_blocked_by_active_maintenance_visit(self):
+		# on_cancel's converted query joins Maintenance Visit Purpose -> Maintenance Visit and
+		# filters the PARENT visit's docstatus != 2; a submitted (non-cancelled) visit referencing
+		# the claim must block cancellation.
+		claim = self.make_warranty_claim()
+		self.make_maintenance_visit_for_claim(claim, "Partially Completed")
+
+		self.assertRaises(frappe.ValidationError, claim.on_cancel)
+
+	def test_on_cancel_allowed_when_no_active_visit(self):
+		# No referencing visit -> the query returns nothing -> the claim is marked Cancelled.
+		claim = self.make_warranty_claim()
+
+		claim.on_cancel()
+
+		self.assertEqual(frappe.db.get_value("Warranty Claim", claim.name, "status"), "Cancelled")

erpnext/support/doctype/warranty_claim/warranty_claim.py

@@ -62,13 +62,20 @@ class WarrantyClaim(TransactionBase):
 			self.resolution_date = now_datetime()
 
 	def on_cancel(self):
-		lst = frappe.get_all(
-			"Maintenance Visit Purpose",
-			filters={"prevdoc_docname": self.name, "docstatus": ["!=", 2]},
-			pluck="parent",
+		mv = frappe.qb.DocType("Maintenance Visit")
+		mvp = frappe.qb.DocType("Maintenance Visit Purpose")
+		# filter the parent Maintenance Visit's docstatus (as the original SQL did), not the child row's
+		visits = (
+			frappe.qb.from_(mvp)
+			.inner_join(mv)
+			.on(mvp.parent == mv.name)
+			.select(mv.name)
+			.where((mvp.prevdoc_docname == self.name) & (mv.docstatus != 2))
+			.limit(500)
+			.run()
 		)
-		if lst:
-			lst1 = ",".join(lst)
+		if visits:
+			lst1 = ",".join(x[0] for x in visits)
 			frappe.throw(_("Cancel Material Visit {0} before cancelling this Warranty Claim").format(lst1))
 		else:
 			self.db_set("status", "Cancelled")