[PATCH] templater: add 'env()' to fetch environment variables

[Yuya Nishihara]

On Sun, 15 Jan 2017 15:30:56 -0500, Matt Harbison wrote:
> # HG changeset patch
> # User Matt Harbison <matt_harbison at yahoo.com>
> # Date 1484508143 18000
> #      Sun Jan 15 14:22:23 2017 -0500
> # Node ID 2ba757de67ce1347d088a4d9f947efe5d407ffdd
> # Parent  4c0a5a256ae806fab18d56b3c44a8d1c98a40ce0
> templater: add 'env()' to fetch environment variables
> 
> Template files ignore custom items in [templates] and [templatealias]
> (presumably by design).  We have a couple repositories that host multiple
> products, and use tags consisting of product, OS, and version.  The {latesttag}
> template supports a filtering pattern, but I didn't see any other way to get the
> customized pattern per product/OS into the file, without duplicating the file
> for each combination.  (Yes, there is %include, but letting the build system
> supply this missing piece means the template file doesn't need maintenance as
> products come and go.)
> 
> diff --git a/mercurial/templater.py b/mercurial/templater.py
> --- a/mercurial/templater.py
> +++ b/mercurial/templater.py
> @@ -14,6 +14,7 @@
>  from .i18n import _
>  from . import (
>      config,
> +    encoding,
>      error,
>      minirst,
>      parser,
> @@ -505,6 +506,20 @@
>  
>      return ''.join(chunks)
>  
> + at templatefunc('env([var])')
> +def env(context, mapping, args):
> +    """A dictionary of environment variables, or the value of the single named
> +    variable."""
> +    if len(args) > 1:
> +        # i18n: "env" is a keyword
> +        raise error.ParseError(_("env expects at most one argument"))
> +
> +    if len(args) == 0:
> +        return encoding.environ
> +
> +    raw = evalstring(context, mapping, args[0])
> +    return pycompat.osgetenv(raw)

This can be a simple {env} (or {environ}) keyword and you can use get()
function, e.g. {get(env, 'pattern')}. showextras() is a good example of
building template dict.