Fixed #30425 -- Handled jinja2.TemplateSyntaxError when rendering a template.

Jinja raises jinja2.TemplateSyntaxError in render() not in
get_template() when it's in an included template.

django/template/backends/jinja2.py

@@ -1,3 +1,5 @@
+from pathlib import Path
+
 import jinja2
 
 from django.conf import settings
@@ -68,7 +70,12 @@ class Template:
             context['csrf_token'] = csrf_token_lazy(request)
             for context_processor in self.backend.template_context_processors:
                 context.update(context_processor(request))
+        try:
             return self.template.render(context)
+        except jinja2.TemplateSyntaxError as exc:
+            new = TemplateSyntaxError(exc.args)
+            new.template_debug = get_exception_info(exc)
+            raise new from exc
 
 
 class Origin:
@@ -88,12 +95,22 @@ def get_exception_info(exception):
     """
     context_lines = 10
     lineno = exception.lineno
-    lines = list(enumerate(exception.source.strip().split("\n"), start=1))
+    source = exception.source
+    if source is None:
+        exception_file = Path(exception.filename)
+        if exception_file.exists():
+            with open(exception_file, 'r') as fp:
+                source = fp.read()
+    if source is not None:
+        lines = list(enumerate(source.strip().split('\n'), start=1))
         during = lines[lineno - 1][1]
         total = len(lines)
         top = max(0, lineno - context_lines - 1)
         bottom = min(total, lineno + context_lines)
-
+    else:
+        during = ''
+        lines = []
+        total = top = bottom = 0
     return {
         'name': exception.filename,
         'message': exception.message,

tests/template_backends/jinja2/template_backends/syntax_error_include.html

@@ -0,0 +1 @@
+{% include "template_backends/syntax_error.html" %}

tests/template_backends/test_jinja2.py

@@ -1,5 +1,5 @@
 from pathlib import Path
-from unittest import skipIf
+from unittest import mock, skipIf
 
 from django.template import TemplateSyntaxError
 from django.test import RequestFactory
@@ -96,3 +96,39 @@ class Jinja2Tests(TemplateStringsTests):
         })
         template = engine.get_template('hello.html')
         self.assertEqual(template.render({'name': 'Joe'}), 'Hello Joe!')
+
+    def test_template_render_nested_error(self):
+        template = self.engine.get_template('template_backends/syntax_error_include.html')
+        with self.assertRaises(TemplateSyntaxError) as e:
+            template.render(context={})
+        debug = e.exception.template_debug
+        self.assertEqual(debug['after'], '')
+        self.assertEqual(debug['before'], '')
+        self.assertEqual(debug['during'], '{% block %}')
+        self.assertEqual(debug['bottom'], 1)
+        self.assertEqual(debug['top'], 0)
+        self.assertEqual(debug['line'], 1)
+        self.assertEqual(debug['total'], 1)
+        self.assertEqual(len(debug['source_lines']), 1)
+        self.assertTrue(debug['name'].endswith('syntax_error.html'))
+        self.assertIn('message', debug)
+
+    def test_template_render_error_nonexistent_source(self):
+        template = self.engine.get_template('template_backends/hello.html')
+        with mock.patch(
+            'jinja2.environment.Template.render',
+            side_effect=jinja2.TemplateSyntaxError('', 1, filename='nonexistent.html'),
+        ):
+            with self.assertRaises(TemplateSyntaxError) as e:
+                template.render(context={})
+        debug = e.exception.template_debug
+        self.assertEqual(debug['after'], '')
+        self.assertEqual(debug['before'], '')
+        self.assertEqual(debug['during'], '')
+        self.assertEqual(debug['bottom'], 0)
+        self.assertEqual(debug['top'], 0)
+        self.assertEqual(debug['line'], 1)
+        self.assertEqual(debug['total'], 0)
+        self.assertEqual(len(debug['source_lines']), 0)
+        self.assertTrue(debug['name'].endswith('nonexistent.html'))
+        self.assertIn('message', debug)