ckan_extends cache depends on template paths

[wardi]

CKAN Version if known (or site URL)

all versions

Please describe the expected behaviour

{% ckan_extends %} should extend templates from the next path in the template paths list

Please describe the actual behaviour

{% ckan_extends %} emits a node with a numeric index into the template path list, which is cached with the rest of the compiled template. If the plugins enabled or template paths change after caching the template {% ckan_extends %} will extend from the wrong position in the template paths list. This behavior could lead to an infinite loop, a skipped intermediate template or a TemplateNotFound error (even for templates present in ckan itself)

What steps can be taken to reproduce the issue?

• create a template using {% ckan_extends %}, enable the jinja2_cache_dir setting
• visit a page that causes the template to be cached
• modify the plugins list to add/remove plugins with template directories or add/remove modify the template_extra_paths setting
• visit the page again for unexpected behavior

This is where the numeric index is added to the extends node, which is cached:

ckan/ckan/lib/jinja_extensions.py

Line 132 in 621b008

magic_filename = '*' + str(index) + '*' + filename

This is where the cached numeric index is used on the current template path list:

ckan/ckan/lib/jinja_extensions.py

Lines 189 to 192 in 621b008

	if template.startswith('*'):
	parts = template.split('*')
	template = parts[2]
	searchpaths = self.searchpath[int(parts[1]) + 1:]

I suggest we switch this to emit the current template directory instead of a number so that we won't get this unexpected behavior.