[PATCH 1 of 2 V2] formatter: reserve _ prefixed keys as internal and don't render

[Yuya Nishihara]

On Tue, 21 Mar 2017 23:49:25 -0700, Gregory Szorc wrote:
> # HG changeset patch
> # User Gregory Szorc <gregory.szorc at gmail.com>
> # Date 1490164306 25200
> #      Tue Mar 21 23:31:46 2017 -0700
> # Node ID ae796e23fd42b036352b298f570af8949c2db2d9
> # Parent  102f291807c92864a2231e5e925d6cd64783bb59
> formatter: reserve _ prefixed keys as internal and don't render
> 
> As part of implementing `hg show`, Yuya noticed that JSON formatting
> was rendering an internal-only key, which was unfortunate.
> 
> In this patch, I document new behavior on fm.data() that all
> keys beginning with underscores are reserved. I change the behavior
> of the JSON formatter to not render keys beginning with underscores.
> 
> I ran the test suite with fm.data() raising if any key with a leading
> underscore was passed in and there were no test failures. So I think
> it is safe to adopt this convention.
> 
> diff --git a/mercurial/formatter.py b/mercurial/formatter.py
> --- a/mercurial/formatter.py
> +++ b/mercurial/formatter.py
> @@ -176,7 +176,11 @@ class baseformatter(object):
>          '''insert context objects to be used to render template keywords'''
>          pass
>      def data(self, **data):
> -        '''insert data into item that's not shown in default output'''
> +        '''insert data into item that's not shown in default output
> +
> +        Keys beginning with '_' are designated as internal and may not be
> +        rendered by all formatters.
> +        '''
>          self._item.update(data)
>      def write(self, fields, deftext, *fielddata, **opts):
>          '''do default text output while assigning data to item'''
> @@ -315,6 +319,9 @@ class jsonformatter(baseformatter):
>          self._out.write("\n {\n")
>          first = True
>          for k, v in sorted(self._item.items()):
> +            # Don't format hidden elements.
> +            if k.startswith('_'):
> +                continue

The idea of using _ prefix seems okay, but I don't think internal keys should
be usable in template. If "longestlen" should be available for user templates,
it shouldn't be _-prefixed.