Re: [PATCH] git-gui: Perform rescan on window focus-in

[Pratyush Yadav <me@yadavpratyush.com>]

On 29/07/19 3:40 AM, Pratyush Yadav wrote:
> Hi Brian,
> 
> On 29/07/19 3:06 AM, brian m. carlson wrote:
>> On 2019-07-28 at 15:17:26, Pratyush Yadav wrote:
>>> If any changes are made to the tree while git-gui is open, the user has
>>> to manually rescan to see those changes in the gui. With this change, a
>>> rescan will be performed whenever the window comes in focus, removing
>>> the need for manual rescans in most cases. A manual rescan will still be
>>> needed when something makes changes to the tree while git-gui is still
>>> in focus.
>>
>> I don't use git-gui, so I have no opinion on this change either way, but
>> I do have some questions.
>>
>> What exactly is involved in a rescan? Is it potentially expensive? If
>> so, it might be better to leave it explicit, since people can
>> accidentally give focus to the wrong window (bad click, focus follows
>> mouse, etc.).
>>
> 
> The function is not documented, and I only started spelunking the code a 
> couple days back, so I'll try to answer with what I know. It might not 
> be the full picture.
> 
> Running git-gui --trace, these commands are executed during a rescan:
> 
> /usr/lib/git-core/git-rev-parse --verify HEAD
> /usr/lib/git-core/git-update-index -q --unmerged --ignore-missing --refresh
> 
> Since I'm not too familiar with the details of these, I'll let you be 
> the judge on how expensive these operations are. But I'll add that 
> rescans are pretty fast on my relatively slow hard disk.
> 
>> Is there ever a situation in which someone might want to see the old
>> state? For example, would a rescan change the active commit shown?
>> Someone might be looking at a particular commit message or object ID for
>> the current commit; would this interfere with that?
> 
> At least in my workflow, there is no such situation. I use git-gui to 
> look at uncommitted changes, and stage and commit them. To look at older 
> commits, I use gitk. And from what I understand, git-gui is not designed 
> to browse old commits. In the options menu, it simply opens gitk if you 
> click "Visualise master's history". There is no history browsing in 
> git-gui itself.
> 
> Yes, a rescan will remove the old commit and will show the latest 
> changes. This includes the old diff that was there before it was 
> committed or removed from outside of git-gui. So this change will 
> certainly interfere with the old state.

To add to this, not rescanning has unwanted side effects too. Say you 
stage a file, and just as you are about to commit you suddenly remember 
one small thing you forgot. So you add that change, and jump back into 
git-gui. It shows your file as staged, and the unstaged changes section 
is empty. So you commit the change. Hit refresh and your last minute 
change didn't make it in the commit, even though the unstaged changes 
list was empty. This can cause some confusion, especially among newcomers.

 From my perspective, there is more to gain from auto rescanning than 
there is to lose.

> 
>>
>>> diff --git a/git-gui/git-gui.sh b/git-gui/git-gui.sh
>>> index 6de74ce639..8ca2033dc8 100755
>>> --- a/git-gui/git-gui.sh
>>> +++ b/git-gui/git-gui.sh
>>> @@ -3849,6 +3849,7 @@ if {[is_enabled transport]} {
>>>   }
>>>   bind .   <Key-F5>     ui_do_rescan
>>> +bind .   <FocusIn>    do_rescan
>>
>> What's the difference between these two? Why are we using do_rescan
>> instead of ui_do_rescan?
>>
> 
> ui_do_rescan changes the focus to the first diff. It is executed when 
> you press F5 or choose Rescan from the menu. do_rescan does not do that.
> 
> Resetting to first diff on focus change will get annoying when you are 
> in the middle of looking at some other file. do_rescan just updates the 
> software state without changing what file you are looking at or where in 
> that file you are looking at.
> 
>>>   bind .   <$M1B-Key-r> ui_do_rescan
>>>   bind .   <$M1B-Key-R> ui_do_rescan
>>>   bind .   <$M1B-Key-s> do_signoff
>>
>> The answers to a lot of these questions can go in your commit message to
>> help reviewers and future readers understand your change better.
>>
> 
> I'm never too sure what I should put in the commit message, so I took 
> the conservative route. I'll add more details in the v2 patch.
> 


-- 
Regards,
Pratyush Yadav