Allow empty lines with discounts or charges, fix empty check

CHANGELOG.md

@@ -10,6 +10,14 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/) and this p
 
 - `org`: `Address` includes `LineOne()`, `LineTwo()`, `CompleteNumber()` methods to help with conversion to other formats with some regional formatting.
 
+### Changes
+
+- `bill`: `Invoice` can now have empty lines if discounts or charges present.
+
+### Fixes
+
+- `bill`: `Invoice` `GetExtensions` method now works correctly if missing totals [Issue #424](https://github.com/invopop/gobl/issues/424).
+
 ## [v0.205.0]
 
 ### Added

bill/invoice.go

@@ -151,7 +151,10 @@ func (inv *Invoice) ValidateWithContext(ctx context.Context) error {
 			validation.By(validateInvoiceCustomer),
 		),
 		validation.Field(&inv.Lines,
-			validation.Required,
+			validation.When(
+				len(inv.Discounts) == 0 && len(inv.Charges) == 0,
+				validation.Required.Error("cannot be empty without discounts or charges"),
+			),
 		),
 		validation.Field(&inv.Discounts),
 		validation.Field(&inv.Charges),

bill/invoice_scenarios.go

@@ -19,9 +19,11 @@ func (inv *Invoice) GetExtensions() []tax.Extensions {
 			exts = append(exts, inv.Tax.Ext)
 		}
 	}
-	for _, cat := range inv.Totals.Taxes.Categories {
-		for _, rate := range cat.Rates {
-			exts = append(exts, rate.Ext)
+	if inv.Totals != nil && inv.Totals.Taxes != nil {
+		for _, cat := range inv.Totals.Taxes.Categories {
+			for _, rate := range cat.Rates {
+				exts = append(exts, rate.Ext)
+			}
 		}
 	}
 	return exts

bill/invoice_scenarios_test.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	"github.com/invopop/gobl/addons/it/sdi"
+	"github.com/invopop/gobl/addons/pt/saft"
 	"github.com/invopop/gobl/bill"
 	"github.com/invopop/gobl/cbc"
 	"github.com/invopop/gobl/tax"
@@ -105,14 +106,23 @@ func TestScenarios(t *testing.T) {
 }
 
 func TestInvoiceGetExtensions(t *testing.T) {
-	inv := baseInvoiceWithLines(t)
-	inv.Addons = tax.WithAddons(sdi.V1)
-	inv.Supplier.TaxID = &tax.Identity{
-		Country: "IT",
-		Code:    "12345678903",
-	}
-	require.NoError(t, inv.Calculate())
-	ext := inv.GetExtensions()
-	assert.Len(t, ext, 2)
-	assert.Equal(t, "FPR12", ext[0][sdi.ExtKeyFormat].String())
+	t.Run("with lines", func(t *testing.T) {
+		inv := baseInvoiceWithLines(t)
+		inv.Addons = tax.WithAddons(sdi.V1)
+		inv.Supplier.TaxID = &tax.Identity{
+			Country: "IT",
+			Code:    "12345678903",
+		}
+		require.NoError(t, inv.Calculate())
+		ext := inv.GetExtensions()
+		assert.Len(t, ext, 2)
+		assert.Equal(t, "FPR12", ext[0][sdi.ExtKeyFormat].String())
+	})
+	t.Run("missing lines", func(t *testing.T) {
+		inv := baseInvoice(t)
+		inv.Addons = tax.WithAddons(saft.V1)
+		require.NoError(t, inv.Calculate())
+		ext := inv.GetExtensions()
+		assert.Len(t, ext, 1)
+	})
 }

bill/invoice_test.go

@@ -1135,6 +1135,26 @@ func TestValidation(t *testing.T) {
 		err := inv.Validate()
 		assert.ErrorContains(t, err, "customer: (name: cannot be blank.).")
 	})
+
+	t.Run("missing lines", func(t *testing.T) {
+		inv := baseInvoice(t)
+		require.NoError(t, inv.Calculate())
+		err := inv.Validate()
+		assert.ErrorContains(t, err, "lines: cannot be empty without discounts or charges.")
+	})
+
+	t.Run("missing lines with charge", func(t *testing.T) {
+		inv := baseInvoice(t)
+		inv.Charges = []*bill.Charge{
+			{
+				Reason: "Testing",
+				Amount: num.MakeAmount(1000, 2),
+			},
+		}
+		require.NoError(t, inv.Calculate())
+		err := inv.Validate()
+		assert.NoError(t, err)
+	})
 }
 
 func TestInvoiceTagsValidation(t *testing.T) {