[PATCH v2] ui: add configoverride context manager

[Augie Fackler]

> On Nov 21, 2016, at 7:24 PM, Kostia Balytskyi <ikostia at fb.com> 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

Queued this, thanks.

> 
> 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')
> +
> class paths(dict):
>     """Represents a collection of paths and their configs.
> 
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