[Resolves #1139] Provide useful info on invalid jinja file (#1142)

The jinja API[1] says it will raise a TemplateNotFound exception
when a template does not exist however that does not seem to be
happening so we need to check before attempting to render the
template.

[1] http://code.nabla.net/doc/jinja2/api/jinja2/environment/jinja2.environment.Environment.html#jinja2.environment.Environment.get_template

sceptre/exceptions.py

@@ -180,3 +180,10 @@ class TemplateHandlerArgumentsInvalidError(SceptreException):
     Error raised when the arguments passed to a Template Handler do not
     adhere to the specified JSON schema.
     """
+
+
+class TemplateNotFoundError(SceptreException):
+    """
+    Error raised when a Template file is not found
+    """
+    pass

sceptre/template_handlers/file.py

@@ -1,4 +1,4 @@
-import os
+# -*- coding: utf-8 -*-
 import sceptre.template_handlers.helper as helper
 
 from pathlib import Path
@@ -42,12 +42,9 @@ def handle(self):
                 with open(path) as template_file:
                     return template_file.read()
             elif input_path.suffix in self.jinja_template_extensions:
-                return helper.render_jinja_template(
-                    os.path.dirname(path),
-                    os.path.basename(path),
-                    {"sceptre_user_data": self.sceptre_user_data},
-                    self.stack_group_config.get("j2_environment", {})
-                )
+                return helper.render_jinja_template(path,
+                                                    {"sceptre_user_data": self.sceptre_user_data},
+                                                    self.stack_group_config.get("j2_environment", {}))
             elif input_path.suffix in self.python_template_extensions:
                 return helper.call_sceptre_handler(path,
                                                    self.sceptre_user_data)

sceptre/template_handlers/helper.py

@@ -5,7 +5,8 @@
 
 from importlib.machinery import SourceFileLoader
 from jinja2 import Environment, select_autoescape, FileSystemLoader, StrictUndefined
-from sceptre.exceptions import TemplateSceptreHandlerError
+from pathlib import Path
+from sceptre.exceptions import TemplateSceptreHandlerError, TemplateNotFoundError
 from sceptre.config import strategies
 
 logger = logging.getLogger(__name__)
@@ -46,7 +47,7 @@ def call_sceptre_handler(path, sceptre_user_data):
     )
 
     if not os.path.isfile(path):
-        raise IOError("No such file or directory: '%s'", path)
+        raise TemplateNotFoundError("No such template file: '%s'", path)
 
     module = SourceFileLoader(path, path).load_module()
 
@@ -104,17 +105,15 @@ def _print_frame(filename, line, fcn, line_text):
         )
 
 
-def render_jinja_template(template_dir, filename, jinja_vars, j2_environment):
+def render_jinja_template(path, jinja_vars, j2_environment):
     """
     Renders a jinja template.
 
     Sceptre supports passing sceptre_user_data to JSON and YAML
     CloudFormation templates using Jinja2 templating.
 
-    :param template_dir: The directory containing the template.
-    :type template_dir: str
-    :param filename: The name of the template file.
-    :type filename: str
+    :param path: The path to the template file.
+    :type path: str
     :param jinja_vars: Dict of variables to render into the template.
     :type jinja_vars: dict
     :param j2_environment: The jinja2 environment.
@@ -123,22 +122,25 @@ def render_jinja_template(template_dir, filename, jinja_vars, j2_environment):
     :returns: The body of the CloudFormation template.
     :rtype: str
     """
-    logger.debug("%s Rendering CloudFormation template", filename)
+    path = Path(path)
+    if not path.exists():
+        raise TemplateNotFoundError("No such template file: '%s'", path)
 
+    logger.debug("%s Rendering CloudFormation template", path)
     default_j2_environment_config = {
         "autoescape": select_autoescape(
             disabled_extensions=('j2',),
             default=True,
         ),
-        "loader": FileSystemLoader(template_dir),
+        "loader": FileSystemLoader(path.parent),
         "undefined": StrictUndefined
     }
     j2_environment_config = strategies.dict_merge(
         default_j2_environment_config, j2_environment
     )
     j2_environment = Environment(**j2_environment_config)
 
-    template = j2_environment.get_template(filename)
+    template = j2_environment.get_template(path.name)
 
     body = template.render(**jinja_vars)
     return body

sceptre/template_handlers/http.py

@@ -1,6 +1,5 @@
 # -*- coding: utf-8 -*-
 import pathlib
-import os
 import requests
 import tempfile
 import sceptre.template_handlers.helper as helper
@@ -52,12 +51,9 @@ def handle(self):
                     f.seek(0)
                     f.read()
                     if path.suffix in self.jinja_template_extensions:
-                        template = helper.render_jinja_template(
-                            os.path.dirname(f.name),
-                            os.path.basename(f.name),
-                            {"sceptre_user_data": self.sceptre_user_data},
-                            self.stack_group_config.get("j2_environment", {})
-                        )
+                        template = helper.render_jinja_template(f.name,
+                                                                {"sceptre_user_data": self.sceptre_user_data},
+                                                                self.stack_group_config.get("j2_environment", {}))
                     elif path.suffix in self.python_template_extensions:
                         template = helper.call_sceptre_handler(
                             f.name,

sceptre/template_handlers/s3.py

@@ -1,6 +1,5 @@
-import logging
+# -*- coding: utf-8 -*-
 import pathlib
-import os
 import tempfile
 import sceptre.template_handlers.helper as helper
 
@@ -17,7 +16,6 @@ class S3(TemplateHandler):
     """
 
     def __init__(self, *args, **kwargs):
-        self.logger = logging.getLogger(__name__)
         super(S3, self).__init__(*args, **kwargs)
 
     def schema(self):
@@ -56,12 +54,9 @@ def handle(self):
                     f.seek(0)
                     f.read()
                     if path.suffix in jinja_template_suffix:
-                        template = helper.render_jinja_template(
-                            os.path.dirname(f.name),
-                            os.path.basename(f.name),
-                            {"sceptre_user_data": self.sceptre_user_data},
-                            self.stack_group_config.get("j2_environment", {})
-                        )
+                        template = helper.render_jinja_template(f.name,
+                                                                {"sceptre_user_data": self.sceptre_user_data},
+                                                                self.stack_group_config.get("j2_environment", {}))
                     elif path.suffix in python_template_suffix:
                         template = helper.call_sceptre_handler(
                             f.name,

tests/test_template.py

@@ -14,7 +14,7 @@
 from sceptre.template import Template
 from sceptre.connection_manager import ConnectionManager
 from sceptre.exceptions import UnsupportedTemplateFileTypeError
-from sceptre.exceptions import TemplateSceptreHandlerError
+from sceptre.exceptions import TemplateSceptreHandlerError, TemplateNotFoundError
 from sceptre.template_handlers import TemplateHandler
 
 
@@ -260,7 +260,7 @@ def test_body_with_chdir_template(self):
 
     def test_body_with_missing_file(self):
         self.template.handler_config["path"] = "incorrect/template/path.py"
-        with pytest.raises(IOError):
+        with pytest.raises(TemplateNotFoundError):
             self.template.body
 
     def test_body_with_python_template(self):

tests/test_template_handlers/test_file.py → tests/test_template_handlers/test_helper.py

@@ -4,6 +4,7 @@
 import yaml
 
 import sceptre.template_handlers.helper as helper
+from sceptre.exceptions import TemplateNotFoundError
 from unittest.mock import patch
 
 
@@ -52,17 +53,20 @@
 """
     )
 ])
-def test_render_jinja_template(filename, sceptre_user_data, expected):
-    jinja_template_dir = os.path.join(
+@patch("pathlib.Path.exists")
+def test_render_jinja_template(mock_pathlib,
+                               filename,
+                               sceptre_user_data,
+                               expected):
+    mock_pathlib.return_value = True
+    jinja_template_path = os.path.join(
         os.getcwd(),
-        "tests/fixtures/templates"
-    )
-    result = helper.render_jinja_template(
-        template_dir=jinja_template_dir,
-        filename=filename,
-        jinja_vars={"sceptre_user_data": sceptre_user_data},
-        j2_environment={}
+        "tests/fixtures/templates",
+        filename
     )
+    result = helper.render_jinja_template(path=jinja_template_path,
+                                          jinja_vars={"sceptre_user_data": sceptre_user_data},
+                                          j2_environment={})
     expected_yaml = yaml.safe_load(expected)
     result_yaml = yaml.safe_load(result)
     assert expected_yaml == result_yaml
@@ -77,17 +81,28 @@ def test_render_jinja_template(filename, sceptre_user_data, expected):
      ["autoescape", "loader", "undefined", "lstrip_blocks", "extensions"])
 ])
 @patch("sceptre.template_handlers.helper.Environment")
-def test_render_jinja_template_j2_environment_config(mock_environment, j2_environment, expected_keys):
+@patch("pathlib.Path.exists")
+def test_render_jinja_template_j2_environment_config(mock_pathlib,
+                                                     mock_environment,
+                                                     j2_environment,
+                                                     expected_keys):
+    mock_pathlib.return_value = True
     filename = "vpc.j2"
     sceptre_user_data = {"vpc_id": "10.0.0.0/16"}
-    jinja_template_dir = os.path.join(
+    jinja_template_path = os.path.join(
         os.getcwd(),
-        "tests/fixtures/templates"
-    )
-    _ = helper.render_jinja_template(
-        template_dir=jinja_template_dir,
-        filename=filename,
-        jinja_vars={"sceptre_user_data": sceptre_user_data},
-        j2_environment=j2_environment
+        "tests/fixtures/templates",
+        filename
     )
+    _ = helper.render_jinja_template(path=jinja_template_path,
+                                     jinja_vars={"sceptre_user_data": sceptre_user_data},
+                                     j2_environment=j2_environment)
     assert list(mock_environment.call_args.kwargs) == expected_keys
+
+
+def test_render_jinja_template_non_existing_file():
+    jinja_template_path = os.path.join("/ref/to/nowhere/boom.j2")
+    with pytest.raises(TemplateNotFoundError):
+        helper.render_jinja_template(path=jinja_template_path,
+                                     jinja_vars={"sceptre_user_data": {}},
+                                     j2_environment={})