Re: [PATCH v4 1/1] Make gitdir work with worktrees, respect core.hooksPath, etc

Hi Pratyush,

On Mon, 14 Oct 2019, Pratyush Yadav wrote:

On 12/10/19 11:24PM, Johannes Schindelin wrote:

quoted

Hi Pratyush,

On Sat, 12 Oct 2019, Pratyush Yadav wrote:

quoted

On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:

quoted

@@ -1453,10 +1501,16 @@ proc rescan {after {honor_trustmtime 1}} {
 	global HEAD PARENT MERGE_HEAD commit_type
 	global ui_index ui_workdir ui_comm
 	global rescan_active file_states
-	global repo_config
+	global repo_config _gitdir_cache

 	if {$rescan_active > 0 || ![lock_index read]} return

+	# Only re-prime gitdir cache on a full rescan
+	if {$after ne "ui_ready"} {

What do you mean by a "full rescan"? I assume you use it as the
differentiator between `ui_do_rescan` (called when you hit F5 or choose
rescan from the menu) and `do_rescan` (called when you revert a line or
hunk), and a "full rescan" refers to `ui_do_rescan`.

Well in that case, this check is incorrect. `do_rescan` passes only
"ui_ready" and `ui_do_rescan` passes "force_first_diff ui_ready".

But either way, I'm not a big fan of this. This check makes assumptions
about the behaviour of its callers based on what they pass to $after.
The way I see it, $after should be a black box to `rescan`, and it
should make absolutely no assumptions about it.

Doing it this way is really brittle, and would break as soon as someone
changes the behaviour of `ui_do_rescan`. If someone in the future passes
a different value in $after, this would stop working as intended and
would not refresh the cached list on a rescan.

So, I think a better place for this if statement would be in
`ui_do_rescan`. This would mean adding a new function that does this.
But if we unset _gitdir_cache in prime_gitdir_cache (I see no reason not
to), we can get away with just something like:

  proc ui_do_rescan {} {
  	rescan {prime_gitdir_cache; ui_ready}
  }

Though since `prime_gitdir_cache` does not really depend on the rescan
being finished, something like this would also work fine:

  proc ui_do_rescan {} {
  	rescan ui_ready
  	prime_gitdir_cache
  }

That was my first attempt. However, there is a very important piece of
code that is even still quoted above: that `if {$rescan_active > 0 ||
![lock_index read]} return` part.

I do _not_ want to interfere with an actively-going-on rescan. If there
is an active one, I don't want to re-prime the `_gitdir` cache.

Good catch! In that case I suppose refreshing the cache in $after would
be the way to go (IOW, the former of my two suggestions). Anything
$after won't get executed if we return early from that check.

The obvious problem with that solution is that the `_gitdir` is reset
_after_ the rescan. In my solution, it is reset _before_, as I have no
idea how often the `_gitdir` values are used during a rescan (and if
none of they were, I would like to be very cautious to prepare for a
future where any of those `_gitdir` values _are_ used during a rescan).

So I am afraid that I find way too serious problems with both of your
proposed alternatives.

Ciao,
Johannes

quoted

That was the reason why I put the additional code into `rescan` rather
than into `ui_do_rescan()`.

Ciao,
Johannes

quoted

This would allow us to do these two things in parallel since `rescan` is
asynchronous. But that would also mean it is possible that the status
bar would show "Ready" while `prime_gitdir_cache` is still executing.

I can't really make up my mind on what is better. I'm inclining on using
the latter way, effectively trading a bit of UI inconsistency for
performance (at least in theory).

Thoughts?

quoted

+		array unset _gitdir_cache
+		prime_gitdir_cache
+	}
+
 	repository_state newType newHEAD newMERGE_HEAD
 	if {[string match amend* $commit_type]
 		&& $newType eq {normal}

--
Regards,
Pratyush Yadav