[FIX] account_global_discount: link line taxes to discount move line

account_global_discount/README.rst

@@ -50,6 +50,13 @@ You can assign global discounts to partners as well:
 #. In section purchase (if the partner is a supplier), you can set purchase
    discounts.
 
+Known issues / Roadmap
+======================
+
+* Global Discount move lines are created for a common base amount. If that
+  wasn't the case, we should split discount move lines between bases and
+  assign proper taxes accordingly.
+
 Bug Tracker
 ===========
 

account_global_discount/models/account_invoice.py

@@ -154,6 +154,9 @@ def invoice_line_move_line_get(self):
                 'price': discount.discount_amount * -1,
                 'account_id': discount.account_id.id,
                 'account_analytic_id': discount.account_analytic_id.id,
+                # TODO: If the base wasn't common to all invoice lines,
+                # we should split discount lines across bases.
+                'tax_ids': self.invoice_line_ids.mapped('tax_ids'),
                 'invoice_id': self.id,
             })
         return res

account_global_discount/readme/ROADMAP.rst

@@ -0,0 +1,3 @@
+* Global Discount move lines are created for a common base amount. If that
+  wasn't the case, we should split discount move lines between bases and
+  assign proper taxes accordingly.