[FIX] sale: invoice multiple SO: right sequence

Have sections order lines on each Sale Order
Have multiple Sale Orders on which the action "invoice order" is triggered
(to make one invoice for all of them)

Before this commit, the real invoice lines were not under their respective
section line
This was because we kept the sequence of the order line when making the order line
which makes little sense in a case where we merge the orders

After this commit, the invoice lines are under their respective section

OPW 1985080

closes odoo/odoo#33219

Signed-off-by: Lucas Perais (lpe) <lpe@odoo.com>

addons/sale/models/sale.py

@@ -516,6 +516,9 @@ class SaleOrder(models.Model):
         invoices_origin = {}
         invoices_name = {}
 
+        # Keep track of the sequences of the lines
+        # To keep lines under their section
+        inv_line_sequence = 0
         for order in self:
             group_key = order.id if grouped else (order.partner_invoice_id.id, order.currency_id.id)
 
@@ -524,6 +527,7 @@ class SaleOrder(models.Model):
 
             # Create lines in batch to avoid performance problems
             line_vals_list = []
+            # sequence is the natural order of order_lines
             for line in order.order_line:
                 if line.display_type == 'line_section':
                     pending_section = line
@@ -545,14 +549,21 @@ class SaleOrder(models.Model):
 
                 if line.qty_to_invoice > 0 or (line.qty_to_invoice < 0 and final):
                     if pending_section:
-                        line_vals_list.extend(pending_section.invoice_line_create_vals(
+                        section_invoice = pending_section.invoice_line_create_vals(
                             invoices[group_key].id,
                             pending_section.qty_to_invoice
-                        ))
+                        )
+                        inv_line_sequence += 1
+                        section_invoice[0]['sequence'] = inv_line_sequence
+                        line_vals_list.extend(section_invoice)
                         pending_section = None
-                    line_vals_list.extend(line.invoice_line_create_vals(
+
+                    inv_line_sequence += 1
+                    inv_line = line.invoice_line_create_vals(
                         invoices[group_key].id, line.qty_to_invoice
-                    ))
+                    )
+                    inv_line[0]['sequence'] = inv_line_sequence
+                    line_vals_list.extend(inv_line)
 
             if references.get(invoices.get(group_key)):
                 if order not in references[invoices[group_key]]: