formatter: add function to convert list to appropriate format (issue5217) Before, it wasn't possible for formatter to handle array structure other than date tuple. We've discussed that at the last sprint, which ended we would probably want to allow only templatable data structure, i.e. a list of dicts: data(tags=[{'tag': a}, {'tag': b}, ...]) Unfortunately, it turned out not working well with template functions: "{ifcontains(a, tags, ...)}" ^^^^^^^^^^^^^^^^^^ "a in tags", where tags should be a plain list/set of tags So the formatter must at least know if the type [{}] was constructed from a plain list or was actually a list of dicts. This patch introduces new explicit interface to convert an array structure to an appropriate data type for the current formatter, which can be used as follows: fm.write('tags', _('tags: %s\n'), fm.formatlist(tags, name='tag')) No separate fm.data() call should be necessary.