[FIX] sale_mrp, sale_stock: procurement qty of kits

- Create a BOM kit for product F with:
  2 Unit(s) of A
  1 Unit(s) of B
- Create a SO for 1 Unit(s) of F, confirm
  => a picking with 2 Unit(s) of A and 1 Unit(s) of B is created
- Modify the Ordered Qty to 2 Unit(s)

The picking is not updated.

This is because `_get_qty_procurement` wrongly computed the product
quantity based on the moves' quantities. This is not correct since the
moves are for products A and B, not product F.

At this point, it is not possible to make sure of the real procurement
quantity. therefore, we use a very simple approach: we compare the sold
quantity before and after modification, and return the difference.

opw-1881227

closes odoo/odoo#27064

addons/sale_mrp/models/sale_mrp.py

@@ -47,6 +47,17 @@ class SaleOrderLine(models.Model):
                 components[product] = {'qty': qty, 'uom': to_uom.id}
         return components
 
+    def _get_qty_procurement(self):
+        self.ensure_one()
+        # Specific case when we change the qty on a SO for a kit product.
+        # We don't try to be too smart and keep a simple approach: we compare the quantity before
+        # and after update, and return the difference. We don't take into account what was already
+        # sent, or any other exceptional case.
+        bom = self.env['mrp.bom']._bom_find(product=self.product_id)
+        if bom and bom.type == 'phantom' and 'previous_product_uom_qty' in self.env.context:
+            return self.env.context['previous_product_uom_qty'].get(self.id, 0.0)
+        return super(SaleOrderLine, self)._get_qty_procurement()
+
 
 class AccountInvoiceLine(models.Model):
     # TDE FIXME: what is this code ??

addons/sale_stock/models/sale_order.py

@@ -99,14 +99,15 @@ class SaleOrderLine(models.Model):
 
     @api.multi
     def write(self, values):
-        lines = False
+        lines = self.env['sale.order.line']
         if 'product_uom_qty' in values:
             precision = self.env['decimal.precision'].precision_get('Product Unit of Measure')
             lines = self.filtered(
                 lambda r: r.state == 'sale' and float_compare(r.product_uom_qty, values['product_uom_qty'], precision_digits=precision) == -1)
+        previous_product_uom_qty = {line.id: line.product_uom_qty for line in lines}
         res = super(SaleOrderLine, self).write(values)
         if lines:
-            lines._action_launch_procurement_rule()
+            lines.with_context(previous_product_uom_qty=previous_product_uom_qty)._action_launch_procurement_rule()
         return res