[PATCH V4] ui: add new config flag for interface selection

[Pierre-Yves David]

On 02/11/2016 05:14 PM, Laurent Charignon wrote:
> # HG changeset patch
> # User Laurent Charignon <lcharignon at fb.com>
> # Date 1455210657 28800
> #      Thu Feb 11 09:10:57 2016 -0800
> # Node ID 53494a3e515b7744759dfa064685b1b8299fffb7
> # Parent  01a5143cd25f285f8c745a92986cd7186bb32c90
> ui: add new config flag for interface selection
>
> This patch introduces a new config flag ui.interface to select the interface
> for interactive commands. It currently only applies to chunks selection.
> The config can be overridden on a per feature basis with the flag
> ui.interface.<feature>.
>
> features for the moment can only be 'chunkselector', moving forward we expect
> to have 'histedit' and other commands there.
>
> If an incorrect value is given to ui.interface we print a warning and use the
> default interface: text. If HGPLAIN is specified we also use the default
> interface: text.

I think we should have a "auto" (name may varies) value, pick the 
currently best interface per subfeature. For example we already have a 
"curses" ui in storage for histedit, but is definitly not polished 
enough yet. We'll want to use curses for chunk selection as a default 
long before we might want curses ui for histedit.

That would be the default. Don't update your patch for that, we can 
follow up on that if people agree.

> diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
> --- a/mercurial/help/config.txt
> +++ b/mercurial/help/config.txt
> @@ -1587,6 +1587,17 @@
>   ``interactive``
>       Allow to prompt the user. (default: True)
>
> +``interface``
> +    Select the default interface for interactive features (default: text).
> +    Possible values are 'text' and 'curses'.
> +
> +``interface.chunkselector``
> +    Select the interface for chunkselection.

"override interactive interface choice for chunk selection"

I think we should also explain what is "chunk selection" here. Most 
people will not be able to link this with "hg commit -i".

Maybe "chunk selection" should be "patch edition" ? (very low confidence 
guess, juste hitting at the idea of having a different name).

> +    Possible values are 'text' and 'curses'.
> +    This config overrides the interface specified by ui.interface.
> +    If ui.interface and ui.interface.chunkselector aren't set, we use the text
> +    interface.

I think the last sentence is implies in the default of ui.interface and 
can be dropped.

>   ``logtemplate``
>       Template string for commands that print changesets.
>
> diff --git a/mercurial/ui.py b/mercurial/ui.py
> --- a/mercurial/ui.py
> +++ b/mercurial/ui.py
> @@ -699,6 +699,73 @@
>               return False
>           return util.isatty(fh)
>
> +    def interface(self, feature):
> +        '''what interface to use for interactive console features?

small nits: we usually use """ for docstring (not ''')

> +
> +        The interface is controlled by the value of `ui.interface` but also by
> +        the value of feature-specific configuration. For example:
> +
> +        ui.interface.histedit = text
> +        ui.interface.chunkselector = curses
> +
> +        Here the features are "histedit" and "chunkselector".
> +
> +        The configuration above means that the default interfaces for commands
> +        is curses, the interface for histedit is text and the interface for
> +        selecting chunk is crecord (the best curses interface available).
> +
> +        Consider the following exemple:
> +        ui.interface = curses
> +        ui.interface.histedit = text
> +
> +        Then histedit will use the text interface and chunkselector will use
> +        the default curses interface (crecord at the moment).
> +        '''
> +        if self.plain():
> +            return "text"
> +
> +        alloweddefaultinterfaces = ("text", "curses")
> +        defaultfeaturesinterfaces = {
> +            "chunkselector": {
> +                "text": "text",
> +                "curses": "crecord"

Why do we need to introduce a mention of crecord here? Could we do all 
this with "curses" and introduce the notion of value's hierarchy later?

small nits: verylowvariablenamestarttohurtreadability.

> +            }
> +        }
> +
> +        # Default interface for all the features
> +        defaultinterface = "text"
> +        i = self.config("ui", "interface", None)
> +        if i is not None:
> +            if i not in alloweddefaultinterfaces:
> +                self.warn(_("invalid value for ui.interface: %s\n") % i)
> +                self.warn(_("(using default interface instead %s)\n")
> +                          % defaultinterface)

We rarely do double line message. Could we fit this on a single line?

> +            else:
> +                defaultinterface = i

This is going to be quite confusing from a code flow perspective. You 
just move the value of a non-default interface into a variable called 
"defaultinterface"

I would use

   interface = self.config(…)
   if invalide(interface):
       warn()
       interface = defaultinterface

instead.

You can also get rid of the 'None' testing by using 'defaultinterface' 
as the fallback value of self.config(…)


> +        # Feature-specific interface
> +        if feature not in defaultfeaturesinterfaces.keys():
> +            # Programming error, not user error
> +            raise ValueError("Unknown feature requested %s" % feature)

If we skip remove the crecord thingy, in my opinion we can drop this 
entirely.

interface('clownyfeature') would return the value in `ui.interface`. And 
possible value of ui.interface MUST be understood by the underlying feature.

> +        availablefeatureinterfaces = defaultfeaturesinterfaces[feature].keys()
> +        defaultinterface = defaultfeaturesinterfaces[feature][defaultinterface]
> +
> +        f = self.config("ui", "interface.%s" % feature, None)
> +        if f is None:
> +            return defaultinterface

Again, we could just use 'defaultinterface' as the fallback value.

> +        else:
> +            if f not in availablefeatureinterfaces:
> +                self.warn(_("invalid value for ui.interface.%s: %s\n")
> +                          % (feature, f))
> +                self.warn(_("(using default interface instead: %s)\n")
> +                          % defaultinterface)

ditto about double line warning.

> +                return defaultinterface
> +            else:
> +                return defaultfeaturesinterfaces[feature][f]
> +
>       def interactive(self):
>           '''is interactive input allowed?


-- 
Pierre-Yves David