bug#50344: C-x v keybinding for vc-print-branch-log

[Dmitry Gutov <dgutov@yandex.ru>]

On 05.10.2021 20:43, Juri Linkov wrote:

>> I'm also thinking of a separate command for branch creation, wrote all
>> that in bug#50643.  Thanks.
> 
> The following patch adds two new branch commands.
> 
>> However, I don't use tags much (besides creation - only "git fetch
>> --tags"), so I cannot add anything meaningful here.
>> Otherwise, the plan for C-x v b prefix looks great.
>> Other commands, like maybe "C-x v b r" - rename, could be added then.
> 
> I can't find the existing vc API method for renaming tags/branches.

I think that's OK.

>> The command could have a mode for specifying START-POINT, so for Git the
>> command becomes "git checkout -b new-branch-name START-POINT".  This
>> could be on C-u (unless there're other frequent "customization" cases).
> 
> The existing API method has no argument for START-POINT.
> Maybe every backend could handle its prefix arg directly
> from current-prefix-arg?  For example,
> 
>   (defun vc-git-create-tag (dir name branchp)
>     (if current-prefix-arg (completion-read "Start point: ") ...

Maybe we should add a new argument, an optional one. Then backends which 
don't support it can continue working without 'C-u' (we can make sure to 
call them with appropriate number of arguments) but will obviously fail 
when passed an extra argument. We could even catch the error and report 
that the backend doesn't support this feature.

But maybe the command should prompt for START-POINT by default: one 
doesn't create branches that often to be bothered by an extra RET, and 
it can be useful to verify the branch you are branching off of every 
time you do it. That would be my preferred behavior. And the 
implementation could be the same if we manage to treat RET as 
unspecified START-POINT.

As long as the ability to read and show the current ref/branch is there 
for most backends (to show it as the default input in the prompt).