Fix backslash escaping inside of jinja2 expressions

Fixes #11891

lib/ansible/template/__init__.py

@@ -48,6 +48,48 @@ NON_TEMPLATED_TYPES = ( bool, Number )
 
 JINJA2_OVERRIDE = '#jinja2:'
 
+def _preserve_backslashes(data, jinja_env):
+    """Double backslashes within jinja2 expressions
+
+    A user may enter something like this in a playbook::
+
+      debug:
+        msg: "Test Case 1\\3; {{ test1_name | regex_replace('^(.*)_name$', '\\1')}}"
+
+    The string inside of the {{ gets interpreted multiple times First by yaml.
+    Then by python.  And finally by jinja2 as part of it's variable.  Because
+    it is processed by both python and jinja2, the backslash escaped
+    characters get unescaped twice.  This means that we'd normally have to use
+    four backslashes to escape that.  This is painful for playbook authors as
+    they have to remember different rules for inside vs outside of a jinja2
+    expression (The backslashes outside of the "{{ }}" only get processed by
+    yaml and python.  So they only need to be escaped once).  The following
+    code fixes this by automatically performing the extra quoting of
+    backslashes inside of a jinja2 expression.
+
+    """
+    if '\\' in data and '{{' in data:
+        new_data = []
+        d2 = jinja_env.preprocess(data)
+        in_var = False
+
+        for token in jinja_env.lex(d2):
+            if token[1] == 'variable_begin':
+                in_var = True
+                new_data.append(token[2])
+            elif token[1] == 'variable_end':
+                in_var = False
+                new_data.append(token[2])
+            elif in_var and token[1] == 'string':
+                # Double backslashes only if we're inside of a jinja2 variable
+                new_data.append(token[2].replace('\\','\\\\'))
+            else:
+                new_data.append(token[2])
+
+        data = ''.join(new_data)
+
+    return data
+
 class Templar:
     '''
     The main class for templating, with the main entry-point of template().
@@ -296,6 +338,8 @@ class Templar:
             myenv.filters.update(self._get_filters())
             myenv.tests.update(self._get_tests())
 
+            data = _preserve_backslashes(data, myenv)
+
             try:
                 t = myenv.from_string(data)
             except TemplateSyntaxError as e:

test/units/template/test_jinja_backslash.py

@@ -0,0 +1,85 @@
+# (c) 2015 Toshio Kuratomi <tkuratomi@ansible.com>
+#
+# This file is part of Ansible
+#
+# Ansible is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# Ansible is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Ansible.  If not, see <http://www.gnu.org/licenses/>.
+
+# Make coding more python3-ish
+from __future__ import (absolute_import, division, print_function)
+__metaclass__ = type
+
+import jinja2
+from ansible.compat.tests import unittest
+
+from ansible.template import _preserve_backslashes
+
+
+class TestBackslashEscape(unittest.TestCase):
+
+    test_data = (
+                # Test backslashes in a filter arg are double escaped
+                dict(
+                    template="{{ 'test2 %s' | format('\\1') }}",
+                    intermediate="{{ 'test2 %s' | format('\\\\1') }}",
+                    expectation="test2 \\1",
+                    args=dict()
+                ),
+                # Test backslashes inside the jinja2 var itself are double
+                # escaped
+                dict(
+                    template="Test 2\\3: {{ '\\1 %s' | format('\\2') }}",
+                    intermediate="Test 2\\3: {{ '\\\\1 %s' | format('\\\\2') }}",
+                    expectation="Test 2\\3: \\1 \\2",
+                    args=dict()
+                ),
+                # Test backslashes outside of the jinja2 var are not double
+                # escaped
+                dict(
+                    template="Test 2\\3: {{ 'test2 %s' | format('\\1') }}; \\done",
+                    intermediate="Test 2\\3: {{ 'test2 %s' | format('\\\\1') }}; \\done",
+                    expectation="Test 2\\3: test2 \\1; \\done",
+                    args=dict()
+                ),
+                # Test backslashes in a variable sent to a filter are handled
+                dict(
+                    template="{{ 'test2 %s' | format(var1) }}",
+                    #intermediate="{{ 'test2 %s' | format('\\\\1') }}",
+                    intermediate="{{ 'test2 %s' | format(var1) }}",
+                    expectation="test2 \\1",
+                    args=dict(var1='\\1')
+                ),
+                # Test backslashes in a variable expanded by jinja2 are double
+                # escaped
+                dict(
+                    template="Test 2\\3: {{ var1 | format('\\2') }}",
+                    intermediate="Test 2\\3: {{ var1 | format('\\\\2') }}",
+                    expectation="Test 2\\3: \\1 \\2",
+                    args=dict(var1='\\1 %s')
+                ),
+            )
+    def setUp(self):
+        self.env = jinja2.Environment()
+
+    def tearDown(self):
+        pass
+
+    def test_backslash_escaping(self):
+
+        for test in self.test_data:
+            intermediate = _preserve_backslashes(test['template'], self.env)
+            self.assertEquals(intermediate, test['intermediate'])
+            template = jinja2.Template(intermediate)
+            args = test['args']
+            self.assertEquals(template.render(**args), test['expectation'])
+