Preserve validation details when rendering labels (#12874)

* Preserve label rendering validation errors

* Preserve label validation diagnostics before output deletion

Keep logging validation errors in both rendering wrappers before re-raising the original exception. LabelTemplate.print deletes failed DataOutput records, so the error log preserves the diagnostic after the result is removed.

Update the mocked tests to require logging while retaining the original validation details.

* Apply Ruff preview formatting to label rendering tests

src/backend/InvenTree/plugin/base/label/mixins.py

@@ -51,6 +51,9 @@ class LabelPrintingMixin:
         """
         try:
             return label.render(instance, request=request, user=user)
+        except ValidationError:
+            log_error('render_to_pdf', plugin=self.slug)
+            raise
         except Exception:
             log_error('render_to_pdf', plugin=self.slug)
             raise ValidationError(_('Error rendering label to PDF'))
@@ -68,6 +71,9 @@ class LabelPrintingMixin:
         """
         try:
             return label.render_as_string(instance, request=request, user=user)
+        except ValidationError:
+            log_error('render_to_html', plugin=self.slug)
+            raise
         except Exception:
             log_error('render_to_html', plugin=self.slug)
             raise ValidationError(_('Error rendering label to HTML'))

src/backend/InvenTree/plugin/base/label/test_label_mixin.py

@@ -5,6 +5,8 @@ import os
 from unittest import mock
 
 from django.apps import apps
+from django.core.exceptions import ValidationError
+from django.test import SimpleTestCase
 from django.urls import reverse
 
 from pdfminer.high_level import extract_text
@@ -24,6 +26,65 @@ from report.tests import PrintTestMixins
 from stock.models import StockItem, StockLocation
 
 
+class LabelRenderingTests(SimpleTestCase):
+    """Test error handling in the label rendering wrappers."""
+
+    def setUp(self):
+        """Create a label plugin without loading the plugin registry."""
+
+        class TestLabelPlugin(LabelPrintingMixin, InvenTreePlugin):
+            NAME = 'Test Label Printer'
+
+        self.plugin = TestLabelPlugin()
+
+    @mock.patch('plugin.base.label.mixins.log_error')
+    def test_validation_errors(self, log_error):
+        """Log validation errors while preserving messages, codes, and parameters."""
+        for wrapper, renderer in [
+            ('render_to_pdf', 'render'),
+            ('render_to_html', 'render_as_string'),
+        ]:
+            with self.subTest(wrapper=wrapper):
+                log_error.reset_mock()
+                error = ValidationError({
+                    'serial': ValidationError(
+                        'Missing serial number for %(part)s',
+                        code='missing_serial',
+                        params={'part': 'Test part'},
+                    )
+                })
+                label = mock.Mock(spec=LabelTemplate)
+                getattr(label, renderer).side_effect = error
+
+                with self.assertRaises(ValidationError) as raised:
+                    getattr(self.plugin, wrapper)(label, mock.sentinel.instance, None)
+
+                self.assertIs(raised.exception, error)
+                self.assertEqual(
+                    raised.exception.message_dict,
+                    {'serial': ['Missing serial number for Test part']},
+                )
+                log_error.assert_called_once_with(wrapper, plugin=self.plugin.slug)
+
+    @mock.patch('plugin.base.label.mixins.log_error')
+    def test_unexpected_errors(self, log_error):
+        """Log unexpected errors and return the existing generic messages."""
+        for wrapper, renderer, message in [
+            ('render_to_pdf', 'render', 'Error rendering label to PDF'),
+            ('render_to_html', 'render_as_string', 'Error rendering label to HTML'),
+        ]:
+            with self.subTest(wrapper=wrapper):
+                log_error.reset_mock()
+                label = mock.Mock(spec=LabelTemplate)
+                getattr(label, renderer).side_effect = RuntimeError('Rendering failed')
+
+                with self.assertRaises(ValidationError) as raised:
+                    getattr(self.plugin, wrapper)(label, mock.sentinel.instance, None)
+
+                self.assertEqual(raised.exception.messages, [message])
+                log_error.assert_called_once_with(wrapper, plugin=self.plugin.slug)
+
+
 class LabelMixinTests(PrintTestMixins, InvenTreeAPITestCase):
     """Test that the Label mixin operates correctly."""