formatter: add fm.nested(field) to either write or build sub items We sometimes need to build nested items by formatter, but there was no convenient way other than building and putting them manually by fm.data(): exts = [] for n, v in extensions: fm.plain('%s %s\n' % (n, v)) exts.append({'name': n, 'ver': v}) fm.data(extensions=exts) This should work for simple cases, but doing this would make it harder to change the underlying data type for better templating support. So this patch provides fm.nested(field), which returns new nested formatter (or self if items aren't structured and just written to ui.) A nested formatter stores items which will later be rendered by the parent formatter. fn = fm.nested('extensions') for n, v in extensions: fn.startitem() fn.write('name ver', '%s %s\n', n, v) fn.end() Nested items are directly exported to a template for now: {extensions % "{name} {ver}\n"} There's no {extensions} nor {join(extensions, sep)} yet. I have a plan for them by extending fm.nested() API, but I want to revisit it after trying out this API in the real world.