Nested repeat variables with same name handled improperly

[d-maurer]

Playing around with a proper error representation for the RepeatDict, I got the impression that nested repeat variables using the same name could be improperly handled.

The following script demonstrates that this is really the case:

>>> from chameleon.zpt.template import PageTemplate
>>> t = PageTemplate("""\
... <div tal:repeat="i (1, 2, 3)">
...   <span tal:content="'%s(%s)' % (i, repeat['i'].index)" />: <span tal:repeat="i (1, 2, 3)" tal:content="i" /></div>
... """)
>>> print (t())
<div>
  <span>1(0)</span>: <span>1</span>
  <span>2</span>
  <span>3</span></div>
<div>
  <span>2(2)</span>: <span>1</span>
  <span>2</span>
  <span>3</span></div>
<div>
  <span>3(2)</span>: <span>1</span>
  <span>2</span>
  <span>3</span></div>

As you see, the inner (i) loop has corrupted the outer repeat item (which is clear as there is a single dict).

Due to macros, a template writer may not know which nested repeat names are used. It may therefore be difficult to avoid the problem.

zope.pagetemplate uses a MultiMapping (essentially a stack of dicts) to avoid this problem. When a scope is entered, a new empty dict is pushed; when a scope is exited, the dict is popped.

[dataflake]

This is a duplicate of #177