From ea4cdf68f4f592bb0a58748857b601d707bffa5c Mon Sep 17 00:00:00 2001
From: Raffael Meyer <14891507+barredterra@users.noreply.github.com>
Date: Sat, 25 Oct 2025 14:38:31 +0200
Subject: [PATCH] feat: warn on multiple class overrides (#34169)

---
 frappe/installer.py |  8 ++++++++
 frappe/migrate.py   | 16 +++++++++++++++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/frappe/installer.py b/frappe/installer.py
index fdfae9daf6..f0827d5315 100644
--- a/frappe/installer.py
+++ b/frappe/installer.py
@@ -296,6 +296,14 @@ def install_app(name, verbose=False, set_as_patched=True, force=False):
 
 	print(f"\nInstalling {name}...")
 
+	other_class_overrides = frappe.get_hooks("override_doctype_class")
+	if (
+		other_class_overrides
+		and app_hooks.override_doctype_class
+		and any(dt in app_hooks.override_doctype_class for dt in other_class_overrides)
+	):
+		click.secho(f"App {name} overrides a doctype that is already overridden by another app.", fg="yellow")
+
 	if name != "frappe":
 		frappe.only_for("System Manager")
 
diff --git a/frappe/migrate.py b/frappe/migrate.py
index 9a7a4adc2d..623fa1bcbe 100644
--- a/frappe/migrate.py
+++ b/frappe/migrate.py
@@ -7,8 +7,11 @@ import json
 import os
 import threading
 import time
+from collections import defaultdict
 from textwrap import dedent
 
+import click
+
 import frappe
 import frappe.model.sync
 import frappe.modules.patch_handler
@@ -24,7 +27,7 @@ from frappe.modules.utils import sync_customizations
 from frappe.search.website_search import build_index_for_all_routes
 from frappe.utils.connections import check_connection
 from frappe.utils.dashboard import sync_dashboards
-from frappe.utils.data import cint
+from frappe.utils.data import cint, comma_and
 from frappe.utils.fixtures import sync_fixtures
 from frappe.website.utils import clear_website_cache
 
@@ -115,10 +118,21 @@ class SiteMigration:
 	@atomic
 	def pre_schema_updates(self):
 		"""Executes `before_migrate` hooks"""
+		overrides = defaultdict(list)
 		for app in frappe.get_installed_apps():
 			for fn in frappe.get_hooks("before_migrate", app_name=app):
 				frappe.get_attr(fn)()
 
+			for doctype in frappe.get_hooks("override_doctype_class", {}, app_name=app).keys():
+				overrides[doctype].append(app)
+
+		for doctype, app_names in overrides.items():
+			if len(app_names) > 1:
+				click.secho(
+					f"The controller for {doctype} is overridden by multiple apps: {comma_and(app_names, add_quotes=False)}.",
+					fg="yellow",
+				)
+
 	@atomic
 	def run_schema_updates(self):
 		"""Run patches as defined in patches.txt, sync schema changes as defined in the {doctype}.json files"""