Fixed issue #113: "Section lambdas mistakenly pushed onto context stack"

HISTORY.rst

@@ -4,7 +4,8 @@ History
 0.6.0 (TBD)
 -----------
 
-* Falsey values now coerced to strings using str().
+* Bugfix: falsey values now coerced to strings using str().
+* Bugfix: section-lambda return values no longer pushed onto context stack.
 
 0.5.1 (2012-04-24)
 ------------------

pystache/renderengine.py

@@ -161,7 +161,12 @@ class RenderEngine(object):
                 # TODO: should we check the arity?
                 template = data(template)
                 parsed_template = self._parse(template, delimiters=delims)
-                data = [data]
+                # Lambdas special case section rendering and bypass pushing
+                # the data value onto the context stack.  Also see--
+                #
+                #   https://github.com/defunkt/pystache/issues/113
+                #
+                return parsed_template.render(context)
             else:
                 # The cleanest, least brittle way of determining whether
                 # something supports iteration is by trying to call iter() on it:

pystache/tests/test_renderengine.py

@@ -501,6 +501,40 @@ class RenderTests(unittest.TestCase, AssertStringMixin):
         context = {'person': 'Mom', 'test': (lambda text: text + " :)")}
         self._assert_render(u'Hi Mom :)', template, context)
 
+    def test_section__lambda__not_on_context_stack(self):
+        """
+        Check that section lambdas are not pushed onto the context stack.
+
+        Even though the sections spec says that section data values should be
+        pushed onto the context stack prior to rendering, this does not apply
+        to lambdas.  Lambdas obey their own special case.
+
+        This test case is equivalent to a test submitted to the Mustache spec here:
+
+          https://github.com/mustache/spec/pull/47 .
+
+        """
+        context = {'foo': 'bar', 'lambda': (lambda text: "{{.}}")}
+        template = '{{#foo}}{{#lambda}}blah{{/lambda}}{{/foo}}'
+        self._assert_render(u'bar', template, context)
+
+    def test_section__lambda__no_reinterpolation(self):
+        """
+        Check that section lambda return values are not re-interpolated.
+
+        This test is a sanity check that the rendered lambda return value
+        is not re-interpolated as could be construed by reading the
+        section part of the Mustache spec.
+
+        This test case is equivalent to a test submitted to the Mustache spec here:
+
+          https://github.com/mustache/spec/pull/47 .
+
+        """
+        template = '{{#planet}}{{#lambda}}dot{{/lambda}}{{/planet}}'
+        context = {'planet': 'Earth', 'dot': '~{{.}}~', 'lambda': (lambda text: "#{{%s}}#" % text)}
+        self._assert_render(u'#~{{.}}~#', template, context)
+
     def test_comment__multiline(self):
         """
         Check that multiline comments are permitted.