better code for checking missing jinja 2 templates

src/packme/PackerTemplate.py

@@ -272,20 +272,23 @@ class PackerTemplate:
         node["provisioners"] = self._provisioners
         node["post-processors"] = self._postprocessors
 
-        env = jinja2.Environment(undefined=jinja2.DebugUndefined)
-        template = env.from_string(repr(node))
-        rendered = template.render(**self._environment)
+        stringified_node = repr(node)
+
+        # Create a jinja evironment for parsing the manifest
+        env = jinja2.Environment()
+        # Parse the string with jinja templates in unrendered state in order to get te set of all jinja templates
+        ast = env.parse(stringified_node)
+        jinja_templates = jinja2.meta.find_undeclared_variables(ast)
+        # Retrieve those templates which are not declared in the environment. These are the undefined templates.
+        undefined = jinja_templates.difference(self._environment.keys())
 
-        # Check if rendering was done correctly
-        ast = env.parse(rendered)
-        undefined = jinja2.meta.find_undeclared_variables(ast)
+        # If there are some undefined templates, stop here.
         if undefined:
             print(f'The following variables are undefined: {undefined!r}')
             sys.exit(1)
-
-        # Replace back %< .* %> to {{ .* }}
-        rendered = rendered.replace("%<","{{")
-        rendered = rendered.replace(">%","}}")
+        
+        template = env.from_string(stringified_node)
+        rendered = template.render(**self._environment)
 
         # Dump to the output file
         with open(output_file, "w") as fout:

templates/base-ill/manifest.yml

@@ -24,7 +24,7 @@ packer:
       boot_wait: 5s
       boot_command:
         - "<tab> "
-        - "preseed/url=http://%< .HTTPIP >%:%< .HTTPPort >%/{{ preseed_file_name }} "
+        - "preseed/url=http://{% raw %}{{ .HTTPIP }}:{{ .HTTPPort }}{% endraw %}/{{ preseed_file_name }} "
         - "auto-install/enable=true "
         - "net.ifnames=0 "
         - "netcfg/get_hostname={{ vm_name }} "
@@ -38,7 +38,7 @@ packer:
         - "passwd/user-password-again= {{ user_password }} "
         - "passwd/root-password={{ root_password }} "
         - "passwd/root-password-again={{ root_password }} "
-        - "no_proxy=%< .HTTPIP >%,{{ no_proxy }} "
+        - "no_proxy={% raw %}{{ .HTTPIP }}{% endraw %},{{ no_proxy }} "
         - "<enter>"
       disk_size: "{{ disk_size }}"
       http_directory: "http"