[FIX] l10n_it_edi: fix support of customers from San Marino

Steps to reproduce:
- Install Accounting, l10n_it_edi and Contacts
- Switch to an Italian company (e.g. IT Company)
- Go to Contacts and create a contact from San Marino:
  * Name: SM customer
  * Country: San Marino
  * Street, City, ZIP: [any]
  * Destination Code: [any]
- Create an invoice:
  * Customer: [the created contact from San Marino]
  * Product: [any]
- Confirm the invoice
- Generate E-invoice XML via "Send & Print" button

Issue:
In the XML, the destination code (i.e. CodiceDestinatario) is the
default one for non-Italian customer (i.e. XXXXXXX).
Also, the VAT number (i.e. IdFiscaleIVA) is the default value for
countries that are not in the European Union (i.e. OO99999999999).
However, since October 2021, San Marino should be handled differently
for Italian electronic invoices.
A specific destination code (i.e. 2R4GTO8) should be used for all
customers from San Marino.

Source: https://www.credemtel.it/fattura-elettronica/fattura-elettronica-san-marino/

Solution:
For customers from San Marino:
- Keep VAT number
- Set "2R4GTO8" as destination code

opw-3819054

closes odoo/odoo#160494

Signed-off-by: Quentin De Paoli <qdp@odoo.com>

addons/l10n_it_edi/models/res_partner.py

@@ -69,6 +69,7 @@ class ResPartner(models.Model):
 
         europe = self.env.ref('base.europe', raise_if_not_found=False)
         in_eu = not europe or not self.country_id or self.country_id in europe.country_ids
+        is_sm = self.country_id and self.country_id.code == "SM"
 
         # VAT number and country code
         normalized_vat = self.vat
@@ -83,7 +84,10 @@ class ResPartner(models.Model):
                 else:
                     normalized_country = normalized_vat[:2].upper()
                     normalized_vat = normalized_vat[2:]
-
+            # If customer is from San Marino
+            elif is_sm:
+                normalized_country = 'SM'
+                normalized_vat = normalized_vat if normalized_vat[:2].isdecimal() else normalized_vat[2:]
             # The Tax Agency arbitrarily decided that non-EU VAT are not interesting,
             # so this default code is used instead
             # Detect the country code from the partner country instead
@@ -106,7 +110,10 @@ class ResPartner(models.Model):
             zipcode = self.zip
             state_code = self.state_id and self.state_id.code
         else:
-            pa_index = 'XXXXXXX'
+            # San Marino is externally integrated with the SdI.
+            # The country as a whole has a single fixed Destination Code.
+            # https://www.agenziaentrate.gov.it/portale/documents/20143/3788702/Modifiche+ProvvedimentonSanMarino+0248717-2021.pdf/429b5571-17b9-0cce-7f62-f79cf53086d7
+            pa_index = '2R4GTO8' if is_sm else 'XXXXXXX'
             zipcode = '00000'
             state_code = False
 

addons/l10n_it_edi/tests/export_xmls/bill_reverse_charge_san_marino.xml

@@ -21,7 +21,7 @@
             <DatiAnagrafici>
                 <IdFiscaleIVA>
                     <IdPaese>SM</IdPaese>
-                    <IdCodice>OO99999999999</IdCodice>
+                    <IdCodice>6784</IdCodice>
                 </IdFiscaleIVA>
                 <Anagrafica>
                     <Denominazione>Prospectra</Denominazione>