[FIX] account_tax_python: product is a template

- Create a new tax, using the 'Python Code' tax computation
- In 'Applicable Code' field, use a field only available on the
`product.product` model (e.g. `product.code`)
- Attach this new tax to a product that is available in the eCommerce
- Access the eCommerce, search for the product if not displayed.

The template `website_sale.products_item` crashes at rendering because
`code` is not available on a `product.template`.

`product` is supposed to be a `product.product` recordset. However, the
method `_get_combination_info` of `sale` is made in such a way that we
can fetch the information of a template, not a product. Utlimately,
methods `compute_all` and `_compute_amount` are called with the wrong
object.

We fall back on the first variant in this case.

opw-2056722

closes odoo/odoo#36134

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

addons/account_tax_python/models/account_tax.py

@@ -28,6 +28,8 @@ class AccountTaxPython(models.Model):
 
     def _compute_amount(self, base_amount, price_unit, quantity=1.0, product=None, partner=None):
         self.ensure_one()
+        if product and product._name == 'product.template':
+            product = product.product_variant_id
         if self.amount_type == 'code':
             company = self.env.user.company_id
             localdict = {'base_amount': base_amount, 'price_unit':price_unit, 'quantity': quantity, 'product':product, 'partner':partner, 'company': company}
@@ -39,6 +41,8 @@ class AccountTaxPython(models.Model):
     def compute_all(self, price_unit, currency=None, quantity=1.0, product=None, partner=None):
         taxes = self.filtered(lambda r: r.amount_type != 'code')
         company = self.env.user.company_id
+        if product and product._name == 'product.template':
+            product = product.product_variant_id
         for tax in self.filtered(lambda r: r.amount_type == 'code'):
             localdict = self._context.get('tax_computation_context', {})
             localdict.update({'price_unit': price_unit, 'quantity': quantity, 'product': product, 'partner': partner, 'company': company})