fix(server): resolve /history 500 error by correcting importlib.resources usage

luigi/server.py

@@ -37,7 +37,6 @@
 
 import atexit
 import datetime
-import importlib
 import json
 import logging
 import os
@@ -157,7 +156,7 @@ def initialize(self, scheduler):
         self._scheduler = scheduler
 
     def get_template_path(self):
-        return importlib.resources.files("templates").name
+        return os.path.join(os.path.dirname(__file__), "templates")
 
 
 class AllRunHandler(BaseTaskHistoryHandler):

test/server_test.py

@@ -483,6 +483,19 @@ def test_get_no_metrics(self):
             patched_write.assert_not_called()
 
 
+def test_get_template_path_returns_existing_directory():
+    """Regression test for https://github.com/spotify/luigi/issues/3415.
+
+    The returned path must point to the luigi/templates directory that
+    tornado uses to render task-history pages.
+    """
+    handler = luigi.server.BaseTaskHistoryHandler(tornado.web.Application(), mock.MagicMock(), scheduler=mock.MagicMock())
+    path = handler.get_template_path()
+    assert os.path.isdir(path), f"get_template_path() returned non-existent directory: {path!r}"
+    assert os.path.basename(path) == "templates"
+    assert os.path.isfile(os.path.join(path, "recent.html"))
+
+
 class FromUtcTest(unittest.TestCase):
     def test_with_microseconds(self):
         """Test parsing UTC time string with microseconds"""