Use PEP451 loader to work around pytest/jinja2 disagreements (#387)

requirements.txt

@@ -7,8 +7,7 @@ docutils>=0.14
 # testing tools
 pylint>=2.3.1
 coverage>=4.5.4
-# https://github.com/pytest-dev/pytest/issues/5392
-pytest==4.5.0
+pytest>=5.3.5
 pytest-cov>=2.7.1
 pytest-random-order>=1.0.4
 hypothesis>=4.32.3

setup.py

@@ -40,7 +40,7 @@ def find_version(*file_paths):
         "boto3>=1.10.20",
         "Jinja2>=2.10",
         "jsonschema>=3.0.1",
-        "pytest==4.5.0",
+        "pytest>=4.5.0",
         "Werkzeug>=0.15",
         "PyYAML>=5.1",
         "requests>=2.22",

src/rpdk/core/plugin_base.py

@@ -1,6 +1,14 @@
+import importlib.util
 from abc import ABC, abstractmethod
+from pathlib import Path
 
-from jinja2 import ChoiceLoader, Environment, PackageLoader, select_autoescape
+from jinja2 import (
+    ChoiceLoader,
+    Environment,
+    FileSystemLoader,
+    PackageLoader,
+    select_autoescape,
+)
 
 from .filters import FILTER_REGISTRY
 
@@ -15,13 +23,18 @@ def _module_name(self):
         return self.MODULE_NAME
 
     def _setup_jinja_env(self, **options):
+
         if "loader" not in options:
-            options["loader"] = ChoiceLoader(
-                [
-                    PackageLoader(self._module_name, "templates/"),
-                    PackageLoader(__name__, "templates/"),
-                ]
-            )
+            # Try loading module with PEP 451 loaders
+            spec = importlib.util.find_spec(self._module_name)
+
+            if spec is None or spec.origin is None:
+                loader = PackageLoader(self._module_name)
+            else:
+                path = Path(spec.origin).resolve(strict=True)
+                loader = FileSystemLoader(str(path.parent / "templates"))
+
+            options["loader"] = ChoiceLoader([loader, PackageLoader(__name__)])
         if "autoescape" not in options:
             options["autoescape"] = select_autoescape(["html", "htm", "xml"])
 

tests/test_plugin_base.py

@@ -1,11 +1,11 @@
 # fixture and parameter have the same name
 # pylint: disable=redefined-outer-name,useless-super-delegation,protected-access
-from unittest.mock import patch
+from unittest.mock import call, patch
 
 import pytest
 
 from rpdk.core.filters import FILTER_REGISTRY
-from rpdk.core.plugin_base import LanguagePlugin
+from rpdk.core.plugin_base import LanguagePlugin, __name__ as plugin_base_name
 
 
 class TestLanguagePlugin(LanguagePlugin):
@@ -66,3 +66,19 @@ def test_language_plugin_setup_jinja_env_overrides(plugin):
 
     for name in FILTER_REGISTRY:
         assert name in env.filters
+
+
+def test_language_plugin_setup_jinja_env_no_spec(plugin):
+    with patch(
+        "rpdk.core.plugin_base.importlib.util.find_spec", return_value=None
+    ) as mock_spec, patch("rpdk.core.plugin_base.PackageLoader") as mock_loader:
+        env = plugin._setup_jinja_env()
+
+    mock_spec.assert_called_once_with(plugin._module_name)
+    mock_loader.assert_has_calls([call(plugin._module_name), call(plugin_base_name)])
+
+    assert env.loader
+    assert env.autoescape
+
+    for name in FILTER_REGISTRY:
+        assert name in env.filters