[PATCH 2 of 5] formatter: add fm.nested(field) to either write or build sub items

[Gregory Szorc]

> On Aug 22, 2016, at 07:44, Yuya Nishihara <yuya at tcha.org> wrote:
> 
> # HG changeset patch
> # User Yuya Nishihara <yuya at tcha.org>
> # Date 1457866779 -32400
> #      Sun Mar 13 19:59:39 2016 +0900
> # Node ID 22b19113435d7e2d0dd0eb8a515d131f2552b8ac
> # Parent  194ac3287b843cad7bf3d21f4f17ac901b070dea
> 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():

If there is always a begin and end call, should we be using a context manager?

> 
>  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.
> 
> diff --git a/mercurial/formatter.py b/mercurial/formatter.py
> --- a/mercurial/formatter.py
> +++ b/mercurial/formatter.py
> @@ -91,11 +91,23 @@ class baseformatter(object):
>     def plain(self, text, **opts):
>         '''show raw text for non-templated mode'''
>         pass
> +    def nested(self, field):
> +        '''sub formatter to store nested data in the specified field'''
> +        self._item[field] = data = []
> +        return _nestedformatter(self._ui, self._converter, data)
>     def end(self):
>         '''end output for the formatter'''
>         if self._item is not None:
>             self._showitem()
> 
> +class _nestedformatter(baseformatter):
> +    '''build sub items and store them in the parent formatter'''
> +    def __init__(self, ui, converter, data):
> +        baseformatter.__init__(self, ui, topic='', opts={}, converter=converter)
> +        self._data = data
> +    def _showitem(self):
> +        self._data.append(self._item)
> +
> def _iteritems(data):
>     '''iterate key-value pairs in stable order'''
>     if isinstance(data, dict):
> @@ -139,6 +151,9 @@ class plainformatter(baseformatter):
>             self._ui.write(deftext % fielddata, **opts)
>     def plain(self, text, **opts):
>         self._ui.write(text, **opts)
> +    def nested(self, field):
> +        # nested data will be directly written to ui
> +        return self
>     def end(self):
>         pass
> 
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