Re: [PATCH] git-diff.txt: prefer not using <commit>..<commit>

From: Elijah Newren <newren@gmail.com>
Date: Mar 18, 2019, 17:59 UTC
Message-ID: <CABPp-BEy9nN=aV8Y+ueYqv299umHoF2E=8D7heJARM4Qa7P5JQ@mail.gmail.com>
In-Reply-To: <bc7c3f9d769b2d5a108ff4cdc3c7277e112fdb56.1552820745.git.liu.denton@gmail.com>

Hi Denton,

Thanks for working on this.  Some thoughts...

On Sun, Mar 17, 2019 at 4:09 AM Denton Liu <liu.denton@gmail.com> wrote:

Show 16 quoted lines

>
> The documentation used to consider
>
>         git diff <commit> <commit>
>
> and
>
>         git diff <commit>..<commit>
>
> to be equal counterparts. However, rev-list-ish commands also use the
> <commit>..<commit> notation, but in a logically conflicting manner which
> was confusing for some users (including me!).
>
> Deprecating the notation entirely is not really an option because it
> would be an arduous process without much end-value. In addition, there
> are some valid use-cases that we don't want to break.

Yes, there were multiple people who commented that they liked to copy-paste the "A..B" output from fetch/pull in combination with diff and log (even though one suggested that this gave the wrong output and what they really wanted was "diff A...B").

However, "removal of functionality" isn't the only form of deprecation/warning. Updating the manpage is another one which you implemented, but I'd like to suggest yet another: Prefix the diff with a warning message, e.g.

"WARNING: You ran 'git diff A..B' (which means the same thing as 'git diff A B'). Many users confuse 'git diff A..B' and 'git diff A...B'. Please see 'git diff --help' for more details."

Having extra text (e.g. commit message or warning) at the beginning of the diff does not prevent tools like patch(1) or git-apply(1) from successfully applying it, it still makes sense to humans (and who as an added bonus happen to be really good at filtering out common messages if they do encounter them more than a few times), and gives us a chance in the future to figure out how to potentially extend the message to make it a deprecation warning and/or provide details about how to change the behavior of '..' to either be an error or behave like triple dots or just not warn.

Elijah