[PATCH v2] pager: migrate heavily-used extension into core

[Augie Fackler]

> On Feb 6, 2017, at 18:04, Sean Farley <sean at farley.io> wrote:
> 
> Augie Fackler <raf at durin42.com> writes:
> 
>> (sending again because this seems to have gotten stuck somewhere...)
>> (+yuya explicitly for chg thoughts, +smf so someone else can forward to the list if it's stuck again)
>> 
>> On Fri, Feb 03, 2017 at 04:16:09PM -0800, Bryan O'Sullivan wrote:
[...]

>> (This design, btw, was inspired by the way git handles paging, where
>> it's largely up to the command to decide if it wants to invoke the
>> pager.)
> 
> If I'm understanding you correctly, this will get rid of the
> pager.attend variable? If that's true, then I fully support that.

Mostly. pager.attend will probably live on as a config knob for users to force paging of commands that don't request it. I can't see it working without that? Though it'd be the alternative form, that looks like

[pager]
attend-foo = yes

> 
>> As a sketch of where this is headed, API-wise:
>> 
>> class ui:
>> def pager(self, command, category):
>>   ""Starts the pager, if desired by the user.
>> 
>>   `command` specifies the current command the user is running,
>>   something like `log` or `shelve`. It should be the whole original
>>   command name, not the partial name or alias name.
>> 
>>   `category` specifies a broad category this pager invocation fits
>>   into. Examples include `diff`, `log`, `status`, `help`. This
>>   allows users to disable paging of entire types of commands easily.
>>   """
>>   # pager starts, self.pageractive=true, etc
>> 
>> @command
>> def shelve(ui, ...):
>> if action == 'list':
>>   ui.pager('shelve', 'diff' if --patch else 'log')
>> ...
>> 
>> @command
>> def summary(ui, ...):
>> ui.pager('summary', 'status')
>> ...
> 
> Would this get rid of the need to set pager.pager=less? I think last
> time the pager was brought up (I believe the Munich sprint), there was a
> consensus on not relying on the existence of less / more / windows
> weirdness.

I don't know about Windows, but I think we should follow git's lead and default to using *a* pager. On debian, that means sensible-pager, on most other unices that means less, on some unfortunate platforms it means more. In-tree, we should probably default to more, with a recommendation that packagers specify a more reasonable default in the system-wide hgrc.

(I've had a PAGER environment variable for longer than I've had my dotfiles source control, but I have no idea how common this is. For some highly unscientific data, I've posted a poll on twitter: https://twitter.com/durin42/status/828742645145075712 - maybe we'll learn something.)

> The API looks pretty good to me. Nothing off the top of my head that I
> can add / question besides what I asked above.