Upgraded variable support met with upgraded conditional support, see examples/playbooks/upgraded_vars.yml

for details!

CHANGELOG.md

@@ -8,7 +8,8 @@ Core Features:
 * capability to set 'all_errors_fatal: True' in a playbook to force any error to stop execution versus
   a whole group or serial block needing to fail
   usable, without breaking the ability to override in ansible
-* ability to use variables from {{ }} syntax in mainline playbooks (work in progress)
+* ability to use variables from {{ }} syntax in mainline playbooks, new 'when' conditional,
+  see examples/playbooks/upgraded_vars.yml
 * can set ansible_private_key_file as an inventory variable (similar to ansible_ssh_host, etc)
 
 Modules added

examples/playbooks/upgraded_vars.yml

@@ -0,0 +1,24 @@
+# in Ansible 1.2 and later, the $foo variable syntax, which is friendly enough for simple things
+# has been upgraded to allow Jinja2 substitiutions as well, which is now the preferred Syntax.
+# here is an example.  Note that Jinja2 conditionals belong only in templates.  Use ansible conditionals
+# in playbooks.
+
+---
+
+  - hosts: all
+
+    tasks:
+      - shell: echo 'hello {{ ansible_hostname.upper() }}'
+
+      - shell: echo 'match'
+        when: 2 == 2
+
+      - shell: echo 'no match'
+        when: 2 == 2 + 1
+
+      - shell: echo '{{ ansible_os_family }}'
+
+      - shell: echo 'Centos'
+        when: ansible_os_family == 'RedHat'
+
+

lib/ansible/playbook/task.py

@@ -71,6 +71,8 @@ class Task(object):
                 else:
                     raise errors.AnsibleError("cannot find lookup plugin named %s for usage in with_%s" % (plugin_name, plugin_name))
 
+            elif x == 'when':
+                ds['when'] = "jinja2_compare %s" % (ds[x])
             elif x.startswith("when_"):
                 if 'when' in ds:
                     raise errors.AnsibleError("multiple when_* statements specified in task %s" % (ds.get('name', ds['action'])))

lib/ansible/runner/__init__.py

@@ -424,6 +424,7 @@ class Runner(object):
             handler = utils.plugins.action_loader.get('async', self)
 
         conditional = utils.template(self.basedir, self.conditional, inject, expand_lists=False)
+
         if not utils.check_conditional(conditional):
             result = utils.jsonify(dict(skipped=True))
             self.callbacks.on_skipped(host, inject.get('item',None))

lib/ansible/utils/__init__.py

@@ -155,13 +155,18 @@ def check_conditional(conditional):
         return conditional
 
     def is_set(var):
-        return not var.startswith("$")
+        return not var.startswith("$") and not '{{' in var
 
     def is_unset(var):
-        return var.startswith("$")
+        return var.startswith("$") or '{{' in var
 
     try:
-        return eval(conditional.replace("\n", "\\n"))
+        conditional = conditional.replace("\n", "\\n")
+        result = eval(conditional)
+        if result not in [ True, False ]:
+            raise errors.AnsibleError("Conditional expression must evaluate to True or False: %s" % conditional)
+        return result
+
     except (NameError, SyntaxError):
         raise errors.AnsibleError("Could not evaluate the expression: " + conditional)
 
@@ -545,6 +550,7 @@ def compile_when_to_only_if(expression):
     # when: int $x in $alist
     # when: float $x > 2 and $y <= $z
     # when: str $x != $y
+    # when: jinja2_compare asdf  # implies {{ asdf }} 
 
     if type(expression) not in [ str, unicode ]:
         raise errors.AnsibleError("invalid usage of when_ operator: %s" % expression)
@@ -562,8 +568,6 @@ def compile_when_to_only_if(expression):
                 tcopy[i] = t
         return " ".join(tcopy)
 
-
-
     # when_failed / when_changed
     elif tokens[0] in [ 'failed', 'changed' ]:
         tcopy = tokens[1:]
@@ -574,8 +578,6 @@ def compile_when_to_only_if(expression):
                 tcopy[i] = t
         return " ".join(tcopy)
 
-
-
     # when_integer / when_float / when_string
     elif tokens[0] in [ 'integer', 'float', 'string' ]:
         cast = None
@@ -602,6 +604,11 @@ def compile_when_to_only_if(expression):
                 tcopy[i] = "(is_set('''%s''') and '''%s'''.lower() not in ('false', 'no', 'n', 'none', '0', ''))" % (t, t)
         return " ".join(tcopy)
 
+    # the stock 'when' without qualification (new in 1.2), assumes Jinja2 terms
+    elif tokens[0] == 'jinja2_compare':
+        # a Jinja2 evaluation that results in something Python can eval!
+        presented = "{% if " + " ".join(tokens[1:]).strip() + " %} True {% else %} False {% endif %}"
+        return presented
     else:
         raise errors.AnsibleError("invalid usage of when_ operator: %s" % expression)
 

lib/ansible/utils/template.py

@@ -232,7 +232,7 @@ def template(basedir, varname, vars, lookup_fatal=True, depth=0, expand_lists=Tr
     ''' templates a data structure by traversing it and substituting for other data structures '''
 
     if isinstance(varname, basestring):
-        if '{{' in varname:
+        if '{{' in varname or '{%' in varname:
             return template_from_string(basedir, varname, vars)
         m = _varFind(basedir, varname, vars, lookup_fatal, depth, expand_lists)
         if not m:
@@ -403,17 +403,13 @@ def _get_filter_plugins():
         FILTER_PLUGINS.update(filters)
     return FILTER_PLUGINS
 
-class J2Undefined(jinja2.runtime.Undefined):
-    def __str__(self):
-        return "{{ %s }}" % self._undefined_name
-    def __unicode__(self):
-        return "{{ %s }}" % self._undefined_name
-
 def template_from_string(basedir, data, vars):
     ''' run a file through the (Jinja2) templating engine '''
+
+    try:
         if type(data) == str:
             data = unicode(data, 'utf-8')
-    environment = jinja2.Environment(trim_blocks=True, undefined=J2Undefined)
+        environment = jinja2.Environment(trim_blocks=True) # undefined=J2Undefined)
         environment.filters.update(_get_filter_plugins())
         # TODO: may need some way of using lookup plugins here seeing we aren't calling
         # the legacy engine, lookup() as a function, perhaps?
@@ -421,4 +417,6 @@ def template_from_string(basedir, data, vars):
         t = environment.from_string(data)
         res = jinja2.utils.concat(t.root_render_func(t.new_context(_jinja2_vars(basedir, vars, t.globals), shared=True)))
         return res
+    except jinja2.exceptions.UndefinedError:
+        return data