[FIX] account: fix fiscal position with delivery address

The goal is to ensure that 2 conditions are met for a fiscal position to
be applied (within the EU):

- The customer must have a valid VAT number from another EU Member State
- The goods must leave the country of origin

closes odoo/odoo#81817

Task: 2596204
X-original-commit: ca0fc6cd
Signed-off-by: Quentin De Paoli <qdp@odoo.com>
Signed-off-by: John Laterre <jol@odoo.com>

addons/account/models/partner.py

@@ -168,11 +168,17 @@ class AccountFiscalPosition(models.Model):
         # This can be easily overridden to apply more complex fiscal rules
         PartnerObj = self.env['res.partner']
         partner = PartnerObj.browse(partner_id)
+        delivery = PartnerObj.browse(delivery_id)
 
-        # if no delivery use invoicing
-        if delivery_id:
-            delivery = PartnerObj.browse(delivery_id)
-        else:
+        company = self.env.company
+        eu_country_codes = set(self.env.ref('base.europe').country_ids.mapped('code'))
+        intra_eu = vat_exclusion = False
+        if company.vat and partner.vat:
+            intra_eu = company.vat[:2] in eu_country_codes and partner.vat[:2] in eu_country_codes
+            vat_exclusion = company.vat[:2] == partner.vat[:2]
+
+        # If company and partner have the same vat prefix (and are both within the EU), use invoicing
+        if not delivery or (intra_eu and vat_exclusion):
             delivery = partner
 
         # partner manually set fiscal position always win