[PATCH v2] ui: add configoverride context manager

[Yuya Nishihara]

On Mon, 21 Nov 2016 16:24:58 -0800, Kostia Balytskyi wrote:
> # HG changeset patch
> # User Kostia Balytskyi <ikostia at fb.com>
> # Date 1479774146 28800
> #      Mon Nov 21 16:22:26 2016 -0800
> # Node ID a7c57b059190f02a450667411d92d9a4862f6375
> # Parent  141b0d27e9e1e846215ead5314237536efc1a185
> ui: add configoverride context manager
> 
> I feel like this idea might've been discussed before, so please
> feel free to point me to the right mailing list entry to read
> about why it should not be done.
> 
> We have a common pattern of the following code:
>     backup = ui.backupconfig(section, name)
>     try:
>         ui.setconfig(section, name, temporaryvalue, source)
>         do_something()
>     finally:
>         ui.restoreconfig(backup)
> 
> IMO, this looks better:
>     with ui.configoverride({(section, name): temporaryvalue}, source):
>         do_something()
> 
> Especially this becomes more convenient when one has to backup multiple
> config values before doing something. In such case, adding a new value
> to backup requires codemod in three places.
> 
> diff --git a/mercurial/ui.py b/mercurial/ui.py
> --- a/mercurial/ui.py
> +++ b/mercurial/ui.py
> @@ -7,6 +7,7 @@
>  
>  from __future__ import absolute_import
>  
> +import contextlib
>  import errno
>  import getpass
>  import inspect
> @@ -1193,6 +1194,23 @@ class ui(object):
>                  " update your code.)") % version
>          self.develwarn(msg, stacklevel=2, config='deprec-warn')
>  
> +    @contextlib.contextmanager
> +    def configoverride(self, overrides, source=""):
> +        """Context manager for temporary config overrides
> +        `overrides` must be a dict of the following structure:
> +        {(section, name) : value}"""
> +        backups = {}
> +        for (section, name), value in overrides.items():
> +            backups[(section, name)] = self.backupconfig(section, name)
> +            self.setconfig(section, name, value, source)
> +        yield
> +        for __, backup in backups.items():
> +            self.restoreconfig(backup)
> +        # just restoring ui.quiet config to the previous value is not enough
> +        # as it does not update ui.quiet class member
> +        if ('ui', 'quiet') in overrides:
> +            self.fixconfig(section='ui')

Missed try-finally ?