[FIX] stock_account: delete COGS when set to draft

- Create a product A, FIFO & Automated
- Create a SO, deliver and invoice
- Post the invoice
- Reset it to draft
- Post the invoice again

The COGS lines are duplicated.

Unlike the other lines, the COGS lines are only added at posting. This
is done in case several invoices are generated in draft, but validated
in an arbitrary order.

We clean up the COGS lines when resetting to draft.

opw-2153695
opw-2152465

closes odoo/odoo#41915

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/stock_account/models/account_move.py

@@ -38,11 +38,20 @@ class AccountMove(models.Model):
         self._stock_account_anglo_saxon_reconcile_valuation()
         return res
 
+    def button_draft(self):
+        res = super(AccountMove, self).button_draft()
+
+        # Unlink the COGS lines generated during the 'post' method.
+        self.mapped('line_ids').filtered(lambda line: line.is_anglo_saxon_line).unlink()
+        return res
+
     def button_cancel(self):
         # OVERRIDE
         res = super(AccountMove, self).button_cancel()
 
         # Unlink the COGS lines generated during the 'post' method.
+        # In most cases it shouldn't be necessary since they should be unlinked with 'button_draft'.
+        # However, since it can be called in RPC, better be safe.
         self.mapped('line_ids').filtered(lambda line: line.is_anglo_saxon_line).unlink()
         return res