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git-gui: respect core.hooksPath, falling back to .git/hooks #361

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62 changes: 58 additions & 4 deletions git-gui.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,7 @@ if {[tk windowingsystem] eq "aqua"} {

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On the Git mailing list, Pratyush Yadav wrote (reply to this):

Hi Johannes,

Thanks for the re-roll. Some comments below...

On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <[email protected]>
> 
> Since v2.9.0, Git knows about the config variable core.hookspath that
> allows overriding the path to the directory containing the Git hooks.
> 
> Since v2.10.0, the `--git-path` option respects that config variable,
> too, so we may just as well use that command.
> 
> Other paths inside `.git` are equally subject to differ from
> `<gitdir>/<path>`, i.e. inside worktrees, where _some_ paths live in the
> "gitdir" and some live in the "commondir" (i.e. the "gitdir" of the main
> worktree).
> 
> For Git versions older than v2.5.0 (which was the first version to
> support the `--git-path` option for the `rev-parse` command), we simply
> fall back to the previous code.
> 
> An original patch handled only the hooksPath setting, however, during
> the code submission it was deemed better to fix all call to the `gitdir`
> function.
> 
> To avoid spawning a gazillion `git rev-parse --git-path` instances, we
> cache the returned paths, priming the cache upon startup in a single
> `git rev-parse invocation` with some paths (that have been
> determined via a typical startup and via grepping the source code for
> calls to the `gitdir` function).
> 
> This fixes https://github.com/git-for-windows/git/issues/1755
> 
> Initial-patch-by: Philipp Gortan <[email protected]>
> Signed-off-by: Johannes Schindelin <[email protected]>
> ---
>  git-gui.sh | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 58 insertions(+), 4 deletions(-)
> 
> diff --git a/git-gui.sh b/git-gui.sh
> index fd476b6999..c684dc7ae1 100755
> --- a/git-gui.sh
> +++ b/git-gui.sh
> @@ -158,6 +158,7 @@ if {[tk windowingsystem] eq "aqua"} {
>  
>  set _appname {Git Gui}
>  set _gitdir {}
> +array set _gitdir_cache {}
>  set _gitworktree {}
>  set _isbare {}
>  set _gitexec {}
> @@ -197,12 +198,59 @@ proc appname {} {
>  	return $_appname
>  }
>  
> +proc prime_gitdir_cache {} {
> +	global _gitdir _gitdir_cache
> +
> +	set gitdir_cmd [list git rev-parse --git-dir]
> +
> +	# `--git-path` is only supported since Git v2.5.0
> +	if {[package vcompare $::_git_version 2.5.0] >= 0} {
> +		# This list was generated from a typical startup as well as from
> +		# grepping through Git GUI's source code.
> +		set gitdir_keys [list \
> +			CHERRY_PICK_HEAD FETCH_HEAD GITGUI_BCK GITGUI_EDITMSG \
> +			GITGUI_MSG HEAD hooks hooks/prepare-commit-msg \
> +			index.lock info info/exclude logs MERGE_HEAD MERGE_MSG \
> +			MERGE_RR objects "objects/4\[0-1\]/*" \
> +			"objects/4\[0-3\]/*" objects/info \
> +			objects/info/alternates objects/pack packed-refs \
> +			PREPARE_COMMIT_MSG rebase-merge/head-name remotes \
> +			rr-cache rr-cache/MERGE_RR SQUASH_MSG \
> +		]
> +
> +		foreach key $gitdir_keys {
> +			lappend gitdir_cmd --git-path $key
> +		}
> +	}
> +
> +	set i -1
> +	foreach path [split [eval $gitdir_cmd] "\n"] {
> +		if {$i eq -1} {
> +			set _gitdir $path
> +		} else {
> +			set _gitdir_cache([lindex $gitdir_keys $i]) $path
> +		}
> +		incr i
> +	}
> +}
> +
>  proc gitdir {args} {
> -	global _gitdir
> +	global _gitdir _gitdir_cache
> +
>  	if {$args eq {}} {
>  		return $_gitdir
>  	}
> -	return [eval [list file join $_gitdir] $args]
> +
> +	set args [eval [list file join] $args]
> +	if {![info exists _gitdir_cache($args)]} {
> +		if {[package vcompare $::_git_version 2.5.0] >= 0} {
> +			set _gitdir_cache($args) [git rev-parse --git-path $args]
> +		} else {
> +			set _gitdir_cache($args) [file join $_gitdir $args]
> +		}
> +	}
> +
> +	return $_gitdir_cache($args)
>  }
>  
>  proc gitexec {args} {
> @@ -1242,7 +1290,7 @@ if {[catch {
>  	&& [catch {
>  		# beware that from the .git dir this sets _gitdir to .
>  		# and _prefix to the empty string
> -		set _gitdir [git rev-parse --git-dir]
> +		prime_gitdir_cache
>  		set _prefix [git rev-parse --show-prefix]
>  	} err]} {
>  	load_config 1

Looks good till here.

> @@ -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
  }

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?

> +		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

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On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Pratyush,

On Sat, 12 Oct 2019, Pratyush Yadav wrote:

> On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
>
> > @@ -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.

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

Ciao,
Johannes

>
> 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?
>
> > +		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
>

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On the Git mailing list, Pratyush Yadav wrote (reply to this):

On 12/10/19 11:24PM, Johannes Schindelin wrote:
> Hi Pratyush,
> 
> On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> 
> > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> >
> > > @@ -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.
 
> That was the reason why I put the additional code into `rescan` rather
> than into `ui_do_rescan()`.
> 
> Ciao,
> Johannes
> 
> >
> > 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?
> >
> > > +		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

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On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Pratyush,

On Mon, 14 Oct 2019, Pratyush Yadav wrote:

> On 12/10/19 11:24PM, Johannes Schindelin wrote:
> > Hi Pratyush,
> >
> > On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> >
> > > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> > >
> > > > @@ -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 cho=
ose
> > > 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 assumpti=
ons
> > > 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 some=
one
> > > changes the behaviour of `ui_do_rescan`. If someone in the future pa=
sses
> > > a different value in $after, this would stop working as intended and
> > > would not refresh the cached list on a rescan.
> > >
> > > So, I think a better place for this if statement would be in
> > > `ui_do_rescan`. This would mean adding a new function that does this=
.
> > > But if we unset _gitdir_cache in prime_gitdir_cache (I see no reason=
 not
> > > to), we can get away with just something like:
> > >
> > >   proc ui_do_rescan {} {
> > >   	rescan {prime_gitdir_cache; ui_ready}
> > >   }
> > >
> > > Though since `prime_gitdir_cache` does not really depend on the resc=
an
> > > being finished, something like this would also work fine:
> > >
> > >   proc ui_do_rescan {} {
> > >   	rescan ui_ready
> > >   	prime_gitdir_cache
> > >   }
> >
> > That was my first attempt. However, there is a very important piece of
> > code that is even still quoted above: that `if {$rescan_active > 0 ||
> > ![lock_index read]} return` part.
> >
> > I do _not_ want to interfere with an actively-going-on rescan. If ther=
e
> > 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

>
> > That was the reason why I put the additional code into `rescan` rather
> > than into `ui_do_rescan()`.
> >
> > Ciao,
> > Johannes
> >
> > >
> > > 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 statu=
s
> > > 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 u=
sing
> > > the latter way, effectively trading a bit of UI inconsistency for
> > > performance (at least in theory).
> > >
> > > Thoughts?
> > >
> > > > +		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
>
>

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On the Git mailing list, Johannes Schindelin wrote (reply to this):

Hi Pratyush,

On Mon, 14 Oct 2019, Pratyush Yadav wrote:

> On 12/10/19 11:24PM, Johannes Schindelin wrote:
> >
> > On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> >
> > > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> > >
> > > > @@ -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 cho=
ose
> > > 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 assumpti=
ons
> > > 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 some=
one
> > > changes the behaviour of `ui_do_rescan`. If someone in the future pa=
sses
> > > a different value in $after, this would stop working as intended and
> > > would not refresh the cached list on a rescan.
> > >
> > > So, I think a better place for this if statement would be in
> > > `ui_do_rescan`. This would mean adding a new function that does this=
.
> > > But if we unset _gitdir_cache in prime_gitdir_cache (I see no reason=
 not
> > > to), we can get away with just something like:
> > >
> > >   proc ui_do_rescan {} {
> > >   	rescan {prime_gitdir_cache; ui_ready}
> > >   }
> > >
> > > Though since `prime_gitdir_cache` does not really depend on the resc=
an
> > > being finished, something like this would also work fine:
> > >
> > >   proc ui_do_rescan {} {
> > >   	rescan ui_ready
> > >   	prime_gitdir_cache
> > >   }
> >
> > That was my first attempt. However, there is a very important piece of
> > code that is even still quoted above: that `if {$rescan_active > 0 ||
> > ![lock_index read]} return` part.
> >
> > I do _not_ want to interfere with an actively-going-on rescan. If ther=
e
> > 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.

But it also won't get executed before the actual rescan. Which is
precisely what I tried to ensure.

Ciao,
Johannes

>
> > That was the reason why I put the additional code into `rescan` rather
> > than into `ui_do_rescan()`.
> >
> > Ciao,
> > Johannes
> >
> > >
> > > 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 statu=
s
> > > 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 u=
sing
> > > the latter way, effectively trading a bit of UI inconsistency for
> > > performance (at least in theory).
> > >
> > > Thoughts?
> > >
> > > > +		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
>

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On the Git mailing list, Pratyush Yadav wrote (reply to this):

On 14/10/19 12:18AM, Johannes Schindelin wrote:
> Hi Pratyush,
> 
> On Mon, 14 Oct 2019, Pratyush Yadav wrote:
> 
> > On 12/10/19 11:24PM, Johannes Schindelin wrote:
> > > Hi Pratyush,
> > >
> > > On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> > >
> > > > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> > > >
> > > > > @@ -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).

_gitdir values are used quite often during a rescan, so yes, this won't 
work.
 
> So I am afraid that I find way too serious problems with both of your
> proposed alternatives.

One alternative I can see right now is adding another optional parameter 
to `rescan` that controls whether we refresh the gitdir cache or not. 
That parameter would default to 0/false. I'm not the biggest fan of 
something like this, but it might be the easiest way to do it given the 
constraints.

I also thought about trying to acquire the index lock in 
`prime_gitdir_cache`, but that could create a race on the lock between 
`prime_gitdir_cache` and `rescan`.

If you have any better ideas, I'm all ears, but otherwise, I maybe our 
best bet is to just go with adding an optional parameter to `rescan`.

-- 
Regards,
Pratyush Yadav

set _appname {Git Gui}
set _gitdir {}
array set _gitdir_cache {}
set _gitworktree {}
set _isbare {}
set _gitexec {}
Expand Down Expand Up @@ -197,12 +198,59 @@ proc appname {} {
return $_appname
}

proc prime_gitdir_cache {} {
global _gitdir _gitdir_cache

set gitdir_cmd [list git rev-parse --git-dir]

# `--git-path` is only supported since Git v2.5.0
if {[package vcompare $::_git_version 2.5.0] >= 0} {
# This list was generated from a typical startup as well as from
# grepping through Git GUI's source code.
set gitdir_keys [list \
CHERRY_PICK_HEAD FETCH_HEAD GITGUI_BCK GITGUI_EDITMSG \
GITGUI_MSG HEAD hooks hooks/prepare-commit-msg \
index.lock info info/exclude logs MERGE_HEAD MERGE_MSG \
MERGE_RR objects "objects/4\[0-1\]/*" \
"objects/4\[0-3\]/*" objects/info \
objects/info/alternates objects/pack packed-refs \
PREPARE_COMMIT_MSG rebase-merge/head-name remotes \
rr-cache rr-cache/MERGE_RR SQUASH_MSG \
]

foreach key $gitdir_keys {
lappend gitdir_cmd --git-path $key
}
}

set i -1
foreach path [split [eval $gitdir_cmd] "\n"] {
if {$i eq -1} {
set _gitdir $path
} else {
set _gitdir_cache([lindex $gitdir_keys $i]) $path
}
incr i
}
}

proc gitdir {args} {
global _gitdir
global _gitdir _gitdir_cache

if {$args eq {}} {
return $_gitdir
}
return [eval [list file join $_gitdir] $args]

set args [eval [list file join] $args]
if {![info exists _gitdir_cache($args)]} {
if {[package vcompare $::_git_version 2.5.0] >= 0} {
set _gitdir_cache($args) [git rev-parse --git-path $args]
} else {
set _gitdir_cache($args) [file join $_gitdir $args]
}
}

return $_gitdir_cache($args)
}

proc gitexec {args} {
Expand Down Expand Up @@ -1242,7 +1290,7 @@ if {[catch {
&& [catch {
# beware that from the .git dir this sets _gitdir to .
# and _prefix to the empty string
set _gitdir [git rev-parse --git-dir]
prime_gitdir_cache
set _prefix [git rev-parse --show-prefix]
} err]} {
load_config 1
Expand Down Expand Up @@ -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"} {
array unset _gitdir_cache
prime_gitdir_cache
}

repository_state newType newHEAD newMERGE_HEAD
if {[string match amend* $commit_type]
&& $newType eq {normal}
Expand Down