[FIX] stock_dropshipping: Updating dropship product

Steps to reproduce the bug:
- Install stock_dropshipping module and enable Routes on SO lines
- Create a storable product P with a supplier S
- Create a SO with P and set this line with the route dropship
- Confirm the SO ( a PO has been created to S with P)
- Change P on the SO with an other product

Bug:

The product P stayed on the PO.
So a product linked to a PO line cannot be changed on a SO.

Do not forward-port in 12.0 and upper

opw:2040249

closes odoo/odoo#35454

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>

addons/stock_dropshipping/__manifest__.py

@@ -22,7 +22,7 @@ internal transfer document is needed.
 """,
     'website': 'https://www.odoo.com/page/warehouse',
     'depends': ['purchase', 'sale_stock'],
-    'data': ['data/stock_data.xml'],
+    'data': ['data/stock_data.xml', 'views/sale_order_views.xml'],
     'test': [
         '../account/test/account_minimal_test.xml',
         '../stock_account/test/stock_valuation_account.xml',

addons/stock_dropshipping/views/sale_order_views.xml

@@ -0,0 +1,25 @@
+<?xml version="1.0"?>
+<odoo>
+    <data>
+        <!-- Do not forward-port in 12.0 and upper -->
+        <record id="view_order_form_inherit_sale_stock" model="ir.ui.view">
+            <field name="name">sale.order.form.sale.dropshipping</field>
+            <field name="model">sale.order</field>
+            <field name="inherit_id" ref="sale.view_order_form"/>
+            <field name="arch" type="xml">
+                <xpath expr="//page/field[@name='order_line']/form//field[@name='product_updatable']" position="after">
+                    <field name="purchase_line_ids" invisible="1"/>
+                </xpath>
+                <xpath expr="//page/field[@name='order_line']/form//field[@name='product_id']" position="attributes">
+                   <attribute name="attrs">{'readonly': ['|', ('product_updatable', '=', False), ('purchase_line_ids', '!=', [])]}</attribute>
+                </xpath>
+                <xpath expr="//page/field[@name='order_line']/tree/field[@name='product_updatable']" position="after">
+                    <field name="purchase_line_ids" invisible="1"/>
+                </xpath>
+                <xpath expr="//page/field[@name='order_line']/tree/field[@name='product_id']" position="attributes">
+                    <attribute name="attrs">{'readonly': ['|', ('product_updatable', '=', False), ('purchase_line_ids', '!=', [])]}</attribute>
+                </xpath>
+           </field>
+        </record>
+    </data>
+</odoo>