Support a whitelisted subset of jinja2 template options

lib/ansible/utils/template.py

@@ -80,6 +80,8 @@ class Flags:
 
 FILTER_PLUGINS = None
 _LISTRE = re.compile(r"(\w+)\[(\d+)\]")
+JINJA2_OVERRIDE = '#jinja2:'
+JINJA2_ALLOWED_OVERRIDES = ['trim_blocks', 'lstrip_blocks', 'newline_sequence', 'keep_trailing_newline']
 
 def lookup(name, *args, **kwargs):
     from ansible import utils
@@ -230,6 +232,18 @@ def template_from_file(basedir, path, vars, vault_password=None):
     except:
         raise errors.AnsibleError("unable to read %s" % realpath)
 
+    # Get jinja env overrides from template
+    if data.startswith(JINJA2_OVERRIDE):
+        eol = data.find('\n')
+        line = data[len(JINJA2_OVERRIDE):eol]
+        data = data[eol+1:]
+        for pair in line.split(','):
+            (key,val) = pair.split(':')
+            key = key.strip()
+            if key in JINJA2_ALLOWED_OVERRIDES:
+                setattr(environment, key, ast.literal_eval(val.strip()))
+
+
     environment.template_class = J2Template
     try:
         t = environment.from_string(data)