Re: Forcing git to use a pager without a tty

[Phillip Wood <phillip.wood123@gmail.com>]

On 23/06/2021 10:05, Phillip Wood wrote:
> Hi Avishay
> 
> On 22/06/2021 23:40, Avishay Matayev wrote:
>> Hi there!
>>
>> Fugitive[1] is a vim plugin that wraps git and many of its commands
>> into the editor in a really awesome way, I won't meddle into it too
>> much as you can read about it in its README, but as you understand, it
>> uses git, a lot.
>>
>> Some git commands use a pager, which is usually a program that needs a
>> pty to function properly (`less`, for example). Fugitive can't really
>> use a pty for the pager as vim runs its subprocesses without a pty.
>> Therefore Fugitive just creates its own pager (which is a simple
>> window in vim) and pastes the git command output there.
> 
> If I understand correctly fugitive is reading the output of the git 
> command over a pipe and putting it into a vim buffer?
> 
>> The only problem left is that Fugitive can't reliably know when git
>> decides to use the pager, for example `git reflog show` does raise the
>> pager while `git reflog expire` does not. Fugitive currently maintains
>> an (very possibly) incomplete list of commands that need a pager but
>> maintaining it manually isn't ideal.
> 
> I don't understand, if as you say above there isn't a pty then git wont 
> use a pager unless GIT_PAGER_IN_USE is set which Fugitive does not seem 
> to,

Sorry that is confused. GIT_PAGER_IN_USE only causes git to act as if a 
pager is being used (for example so it colors things as if it was 
outputting to a tty), it does not invoke the pager

  so I'm not sure what you mean by 'Fugitive can't reliably know when
> git decides to use the pager'

I'm still confused by this - if there is no tty git wont use a pager.

Best Wishes

Phillip

>> I started discussing this on an issue in Fugitive's github page[2] and
>> Tim Pope (the creator and maintainer of Fugitive, thank you!)
>> explained that `git` doesn't use a pager if there is no pty so it's
>> impossible to override its behavior.
>>
>> We had some ideas how to make this feasible (as you can read on the
>> thread) but for brevity's sake I'll present the best (IMO) idea:
>> Essentially, at `pager.c`, don't short-circuit in `git_pager` (or
>> `setup_pager`?) due to pty absence if a new environment variable is
>> present, perhaps something like `GIT_PAGER_FORCE` which will override
>> the `PAGER` and `GIT_PAGER` variables. This will allow Fugitive to
>> apply custom logic through to pager to know if one exists and present
>> the window in vim.
> 
> I note that the latest comment [1] on the github issue talks about a 
> different solution that would cause all git commands to behave as if 
> there was a pty present.
> 
> [1] 
> https://github.com/tpope/vim-fugitive/issues/1772#issuecomment-866401942
> 
> Best Wishes
> 
> Phillip
> 
>> I will appreciate any written thoughts on the matter, thank you :)
>>
>> P.S. I am a complete newbie in regards to mailing lists etiquette,
>> pardon me if I've done anything incorrect
>> P.P.S. I CC'd Junio C Hamano because he signed off on (almost?) all
>> changes to `pager.c`, sorry if that was wrong of me (You probably got
>> this mail twice because of a misconfiguration, oops)
>>
>>
>> 1. https://github.com/tpope/vim-fugitive
>> 2. https://github.com/tpope/vim-fugitive/issues/1772
>>