Re: Forcing git to use a pager without a tty

From: Phillip Wood <phillip.wood123@gmail.com>
Date: Jun 23, 2021, 09:05 UTC
Message-ID: <077d147c-c22f-6463-6545-3aa991e7868b@gmail.com>
In-Reply-To: <CAJ-0OswsrnAuCwU6U=S2i1qKkg=66U-8RHSGqD2kh9T_30Yw9w@mail.gmail.com>

Hi Avishay

On 22/06/2021 23:40, Avishay Matayev wrote:

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> 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?

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

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> 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

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> 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
>