[PATCH 4 of 4 NEW-CONCEPT] track-tags: write all tag changes to a file

[Yuya Nishihara]

On Thu, 6 Apr 2017 01:09:47 +0200, Pierre-Yves David wrote:
> On 04/05/2017 10:54 PM, Jun Wu wrote:
> > I don't think "writing things that hook *may* need to filesystem" is a good
> > approach. It introduces unnecessary overhead if the hook does not need that
> > information.
> 
> I do not find the overhead concerning.
> 
> The thing to keep in mind is that if they are many things to write down, 
> this also means many thing changed during the transaction. So the 
> overhead is likely minimal. In the tags cases, just updating the various 
> tags related cache is going to be much more expensive that writing this 
> to disk.

I agree Pierre-Yves in that I/O overhead wouldn't matter. On the other hand,
I think the slowness of calling back an hg command doesn't matter, too.

As the journal extension collects similar information for bookmarks, can't
we integrate the tag tracking with the journal? Maybe a hook will receive
some pointer to select the corresponding journal entry, and run "hg journal".