[IMP] stock: onchange on inv. line serial number

On Inventory Adjustment lines view, when you set serial number for a
tracked product, its quantity is automatically set on 1.

Task #2025397

closes odoo/odoo#34301

Signed-off-by: Simon Lejeune (sle) <sle@openerp.com>

addons/stock/models/stock_inventory.py

@@ -352,6 +352,7 @@ class InventoryLine(models.Model):
 
     @api.onchange('product_id', 'location_id', 'product_uom_id', 'prod_lot_id', 'partner_id', 'package_id')
     def _onchange_quantity_context(self):
+        product_qty = False
         if self.product_id:
             self.product_uom_id = self.product_id.uom_id
         if self.product_id and self.location_id and self.product_id.uom_id.category_id == self.product_uom_id.category_id:  # TDE FIXME: last part added because crash
@@ -365,9 +366,18 @@ class InventoryLine(models.Model):
             )
         else:
             theoretical_qty = 0
-        # We update `product_qty` only if it equals to `theoretical_qty` to
-        # avoid to reset quantity when user manually set it.
-        if self.product_qty == self.theoretical_qty:
+        # Sanity check on the lot.
+        if self.prod_lot_id:
+            if self.product_id.tracking == 'none' or self.product_id != self.prod_lot_id.product_id:
+                self.prod_lot_id = False
+
+        if self.prod_lot_id and self.product_id.tracking == 'serial':
+            # We force `product_qty` to 1 for SN tracked product because it's
+            # the only relevant value aside 0 for this kind of product.
+            self.product_qty = 1
+        elif self.product_id and float_compare(self.product_qty, self.theoretical_qty, precision_rounding=self.product_uom_id.rounding) == 0:
+            # We update `product_qty` only if it equals to `theoretical_qty` to
+            # avoid to reset quantity when user manually set it.
             self.product_qty = theoretical_qty
         self.theoretical_qty = theoretical_qty