Experiments to demonstrate that we can get a traceback when using a Loader

This is not a patch to add traceback support, just a way to proove that with a loader instead of from_string the traceback properly contain the template code and can be debugged using pdb

slapos/recipe/template/jinja2_template.py

@@ -125,6 +125,15 @@ class FolderLoader(RecipeBaseLoader):
             return path
         return None
 
+class MyLoader(BaseLoader):
+    def __init__(self, file_name, source):
+        self.file_name = file_name
+        self.source = source
+
+    def get_source(self, environment, template):
+        return self.source, self.file_name, lambda: True
+
+
 LOADER_TYPE_DICT = {
     'rawfile': (FileLoader, EXPRESSION_HANDLER['raw']),
     'file': (FileLoader, getKey),
@@ -140,9 +149,11 @@ class Recipe(object):
     def __init__(self, buildout, name, options):
         template = options['template']
         if template.startswith('inline:'):
+            self.template_name = "inline"
             template = template[7:].lstrip('\r\n')
             self.get_template = lambda: template
         else:
+            self.template_name = template
             template = zc.buildout.download.Download(
                 buildout['buildout'],
                 hash_name=True,
@@ -212,9 +223,9 @@ class Recipe(object):
                     Environment(
                         extensions=self.extension_list,
                         undefined=StrictUndefined,
-                        loader=self.loader,
-                    ).from_string(
-                        self.get_template(),
+                        loader=MyLoader(self.template_name, self.get_template())
+                    ).get_template(
+                        self.template_name
                     ).render(
                         **self.context
                     )