[FIX] product: improve variant-template consistency in supplierinfo

Versions
--------
15.0+

Steps
-----
1. Go to Purchase;
2. create a Vendor Pricelist;
3. select a Product, a Product Variant & a Unit Price;
4. empty the Product field & save;
5. create a RFQ;
6. add the Product Variant from the Vendor Pricelist.

Issue
-----
The product's price remains 0.

Cause
-----
The `seller_ids` field in `product.template` creates one-to-many
relation with `product.supplierinfo`'s `product_tmpl_id` field. While it
is possible to select a specific product variant and have the product
field empty, this renders the Vendor Pricelist unavailable for Purchase
Orders.

Solution
--------
Add a `_sanitize_vals` method to `product.supplierinfo` to be used on
create/write, which ensures that if there's a `product_id`, the record's
`product_tmpl_id` is consistent with it. This allows for record imports
to be usable & consistent when only a variant is specified.

Also backport a modified  `onchange` method added in
5537090. Originally it only reset
`product_id` if `product_tmpl_id` was changed to a different non-falsy
value. Modified, it also resets `product_id` if `product_tmpl_id` is
changed to a falsy value, as it would otherwise just re-add the removed
value on create/write after this commit.

opw-3664524

closes odoo#151210

X-original-commit: 5721223
Signed-off-by: Levi Siuzdak <sile@odoo.com>
Signed-off-by: William Henrotin (whe) <whe@odoo.com>

addons/product/models/product_supplierinfo.py

@@ -73,7 +73,8 @@ def _compute_price_discounted(self):
 
     @api.onchange('product_tmpl_id')
     def _onchange_product_tmpl_id(self):
-        if self.product_id and self.product_tmpl_id and self.product_id not in self.product_tmpl_id.product_variant_ids:
+        """Clear product variant if it no longer matches the product template."""
+        if self.product_id and self.product_id not in self.product_tmpl_id.product_variant_ids:
             self.product_id = False
 
     @api.model
@@ -82,3 +83,19 @@ def get_import_templates(self):
             'label': _('Import Template for Vendor Pricelists'),
             'template': '/product/static/xls/product_supplierinfo.xls'
         }]
+
+    def _sanitize_vals(self, vals):
+        """Sanitize vals to sync product variant & template on read/write."""
+        if 'product_id' in vals and 'product_tmpl_id' not in vals:
+            product = self.env['product.product'].browse(vals['product_id'])
+            vals['product_tmpl_id'] = product.product_tmpl_id.id
+
+    @api.model_create_multi
+    def create(self, vals_list):
+        for vals in vals_list:
+            self._sanitize_vals(vals)
+        return super().create(vals_list)
+
+    def write(self, vals):
+        self._sanitize_vals(vals)
+        return super().write(vals)

addons/product/tests/test_seller.py

@@ -135,3 +135,14 @@ def test_40_seller_min_qty_precision(self):
 
         # Assert: The set value is kept
         self.assertEqual(supplier_info.min_qty, precise_value)
+
+    def test_50_seller_ids(self):
+        vendors = self.env['product.supplierinfo'].create([{
+            'partner_id': self.asustec.id,
+            'product_tmpl_id': self.product_consu.product_tmpl_id.id,
+        }, {
+            'partner_id': self.camptocamp.id,
+            'product_id': self.product_consu.id,
+        }])
+        self.assertEqual(vendors, self.product_consu.seller_ids,
+            "Sellers of a product should be listed in the product's seller_ids")