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.

mercurial/formatter.py

@@ -1,302 +1,317 b''
 # formatter.py - generic output formatting for mercurial
 #
 # Copyright 2012 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import os
 
 from .i18n import _
 from .node import (
     hex,
     short,
 )
 
 from . import (
     encoding,
     error,
     templatekw,
     templater,
     util,
 )
 
 pickle = util.pickle
 
 class _nullconverter(object):
     '''convert non-primitive data types to be processed by formatter'''
     @staticmethod
     def formatdate(date, fmt):
         '''convert date tuple to appropriate format'''
         return date
     @staticmethod
     def formatdict(data, key, value, fmt, sep):
         '''convert dict or key-value pairs to appropriate dict format'''
         # use plain dict instead of util.sortdict so that data can be
         # serialized as a builtin dict in pickle output
         return dict(data)
     @staticmethod
     def formatlist(data, name, fmt, sep):
         '''convert iterable to appropriate list format'''
         return list(data)
 
 class baseformatter(object):
     def __init__(self, ui, topic, opts, converter):
         self._ui = ui
         self._topic = topic
         self._style = opts.get("style")
         self._template = opts.get("template")
         self._converter = converter
         self._item = None
         # function to convert node to string suitable for this output
         self.hexfunc = hex
     def __nonzero__(self):
         '''return False if we're not doing real templating so we can
         skip extra work'''
         return True
     def _showitem(self):
         '''show a formatted item once all data is collected'''
         pass
     def startitem(self):
         '''begin an item in the format list'''
         if self._item is not None:
             self._showitem()
         self._item = {}
     def formatdate(self, date, fmt='%a %b %d %H:%M:%S %Y %1%2'):
         '''convert date tuple to appropriate format'''
         return self._converter.formatdate(date, fmt)
     def formatdict(self, data, key='key', value='value', fmt='%s=%s', sep=' '):
         '''convert dict or key-value pairs to appropriate dict format'''
         return self._converter.formatdict(data, key, value, fmt, sep)
     def formatlist(self, data, name, fmt='%s', sep=' '):
         '''convert iterable to appropriate list format'''
         # name is mandatory argument for now, but it could be optional if
         # we have default template keyword, e.g. {item}
         return self._converter.formatlist(data, name, fmt, sep)
     def data(self, **data):
         '''insert data into item that's not shown in default output'''
         self._item.update(data)
     def write(self, fields, deftext, *fielddata, **opts):
         '''do default text output while assigning data to item'''
         fieldkeys = fields.split()
         assert len(fieldkeys) == len(fielddata)
         self._item.update(zip(fieldkeys, fielddata))
     def condwrite(self, cond, fields, deftext, *fielddata, **opts):
         '''do conditional write (primarily for plain formatter)'''
         fieldkeys = fields.split()
         assert len(fieldkeys) == len(fielddata)
         self._item.update(zip(fieldkeys, fielddata))
     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):
         return sorted(data.iteritems())
     return data
 
 class _plainconverter(object):
     '''convert non-primitive data types to text'''
     @staticmethod
     def formatdate(date, fmt):
         '''stringify date tuple in the given format'''
         return util.datestr(date, fmt)
     @staticmethod
     def formatdict(data, key, value, fmt, sep):
         '''stringify key-value pairs separated by sep'''
         return sep.join(fmt % (k, v) for k, v in _iteritems(data))
     @staticmethod
     def formatlist(data, name, fmt, sep):
         '''stringify iterable separated by sep'''
         return sep.join(fmt % e for e in data)
 
 class plainformatter(baseformatter):
     '''the default text output scheme'''
     def __init__(self, ui, topic, opts):
         baseformatter.__init__(self, ui, topic, opts, _plainconverter)
         if ui.debugflag:
             self.hexfunc = hex
         else:
             self.hexfunc = short
     def __nonzero__(self):
         return False
     def startitem(self):
         pass
     def data(self, **data):
         pass
     def write(self, fields, deftext, *fielddata, **opts):
         self._ui.write(deftext % fielddata, **opts)
     def condwrite(self, cond, fields, deftext, *fielddata, **opts):
         '''do conditional write'''
         if cond:
             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
 
 class debugformatter(baseformatter):
     def __init__(self, ui, topic, opts):
         baseformatter.__init__(self, ui, topic, opts, _nullconverter)
         self._ui.write("%s = [\n" % self._topic)
     def _showitem(self):
         self._ui.write("    " + repr(self._item) + ",\n")
     def end(self):
         baseformatter.end(self)
         self._ui.write("]\n")
 
 class pickleformatter(baseformatter):
     def __init__(self, ui, topic, opts):
         baseformatter.__init__(self, ui, topic, opts, _nullconverter)
         self._data = []
     def _showitem(self):
         self._data.append(self._item)
     def end(self):
         baseformatter.end(self)
         self._ui.write(pickle.dumps(self._data))
 
 def _jsonifyobj(v):
     if isinstance(v, dict):
         xs = ['"%s": %s' % (encoding.jsonescape(k), _jsonifyobj(u))
               for k, u in sorted(v.iteritems())]
         return '{' + ', '.join(xs) + '}'
     elif isinstance(v, (list, tuple)):
         return '[' + ', '.join(_jsonifyobj(e) for e in v) + ']'
     elif v is None:
         return 'null'
     elif v is True:
         return 'true'
     elif v is False:
         return 'false'
     elif isinstance(v, (int, float)):
         return str(v)
     else:
         return '"%s"' % encoding.jsonescape(v)
 
 class jsonformatter(baseformatter):
     def __init__(self, ui, topic, opts):
         baseformatter.__init__(self, ui, topic, opts, _nullconverter)
         self._ui.write("[")
         self._ui._first = True
     def _showitem(self):
         if self._ui._first:
             self._ui._first = False
         else:
             self._ui.write(",")
 
         self._ui.write("\n {\n")
         first = True
         for k, v in sorted(self._item.items()):
             if first:
                 first = False
             else:
                 self._ui.write(",\n")
             self._ui.write('  "%s": %s' % (k, _jsonifyobj(v)))
         self._ui.write("\n }")
     def end(self):
         baseformatter.end(self)
         self._ui.write("\n]\n")
 
 class _templateconverter(object):
     '''convert non-primitive data types to be processed by templater'''
     @staticmethod
     def formatdate(date, fmt):
         '''return date tuple'''
         return date
     @staticmethod
     def formatdict(data, key, value, fmt, sep):
         '''build object that can be evaluated as either plain string or dict'''
         data = util.sortdict(_iteritems(data))
         def f():
             yield _plainconverter.formatdict(data, key, value, fmt, sep)
         return templatekw._hybrid(f(), data, lambda k: {key: k, value: data[k]},
                                   lambda d: fmt % (d[key], d[value]))
     @staticmethod
     def formatlist(data, name, fmt, sep):
         '''build object that can be evaluated as either plain string or list'''
         data = list(data)
         def f():
             yield _plainconverter.formatlist(data, name, fmt, sep)
         return templatekw._hybrid(f(), data, lambda x: {name: x},
                                   lambda d: fmt % d[name])
 
 class templateformatter(baseformatter):
     def __init__(self, ui, topic, opts):
         baseformatter.__init__(self, ui, topic, opts, _templateconverter)
         self._topic = topic
         self._t = gettemplater(ui, topic, opts.get('template', ''))
     def _showitem(self):
         g = self._t(self._topic, ui=self._ui, **self._item)
         self._ui.write(templater.stringify(g))
 
 def lookuptemplate(ui, topic, tmpl):
     # looks like a literal template?
     if '{' in tmpl:
         return tmpl, None
 
     # perhaps a stock style?
     if not os.path.split(tmpl)[0]:
         mapname = (templater.templatepath('map-cmdline.' + tmpl)
                    or templater.templatepath(tmpl))
         if mapname and os.path.isfile(mapname):
             return None, mapname
 
     # perhaps it's a reference to [templates]
     t = ui.config('templates', tmpl)
     if t:
         return templater.unquotestring(t), None
 
     if tmpl == 'list':
         ui.write(_("available styles: %s\n") % templater.stylelist())
         raise error.Abort(_("specify a template"))
 
     # perhaps it's a path to a map or a template
     if ('/' in tmpl or '\\' in tmpl) and os.path.isfile(tmpl):
         # is it a mapfile for a style?
         if os.path.basename(tmpl).startswith("map-"):
             return None, os.path.realpath(tmpl)
         tmpl = open(tmpl).read()
         return tmpl, None
 
     # constant string?
     return tmpl, None
 
 def gettemplater(ui, topic, spec):
     tmpl, mapfile = lookuptemplate(ui, topic, spec)
     assert not (tmpl and mapfile)
     if mapfile:
         return templater.templater.frommapfile(mapfile)
     return maketemplater(ui, topic, tmpl)
 
 def maketemplater(ui, topic, tmpl, filters=None, cache=None):
     """Create a templater from a string template 'tmpl'"""
     aliases = ui.configitems('templatealias')
     t = templater.templater(filters=filters, cache=cache, aliases=aliases)
     if tmpl:
         t.cache[topic] = tmpl
     return t
 
 def formatter(ui, topic, opts):
     template = opts.get("template", "")
     if template == "json":
         return jsonformatter(ui, topic, opts)
     elif template == "pickle":
         return pickleformatter(ui, topic, opts)
     elif template == "debug":
         return debugformatter(ui, topic, opts)
     elif template != "":
         return templateformatter(ui, topic, opts)
     # developer config: ui.formatdebug
     elif ui.configbool('ui', 'formatdebug'):
         return debugformatter(ui, topic, opts)
     # deprecated config: ui.formatjson
     elif ui.configbool('ui', 'formatjson'):
         return jsonformatter(ui, topic, opts)
     return plainformatter(ui, topic, opts)