[v4,1/1] Make gitdir work with worktrees, respect core.hooksPath, etc
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Message ID 2f55d6fb2a158c5b26b93ddb9c144ce1af5d9c32.1570534405.git.gitgitgadget@gmail.com
State New
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Series
  • git-gui: respect core.hooksPath, falling back to .git/hooks
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Commit Message

erik chen via GitGitGadget Oct. 8, 2019, 11:33 a.m. UTC
From: Johannes Schindelin <Johannes.Schindelin@gmx.de>

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 <philipp@gortan.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 git-gui.sh | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 58 insertions(+), 4 deletions(-)

Comments

Pratyush Yadav Oct. 11, 2019, 10:26 p.m. UTC | #1
Hi Johannes,

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

On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
> 
> 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 <philipp@gortan.org>
> Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> ---
>  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}
Johannes Schindelin Oct. 12, 2019, 9:24 p.m. UTC | #2
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]
> >  		&& $newType eq {normal}
>
> --
> Regards,
> Pratyush Yadav
>
Pratyush Yadav Oct. 13, 2019, 6:55 p.m. UTC | #3
On 12/10/19 11:24PM, Johannes Schindelin wrote:
> Hi Pratyush,
> 
> On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> 
> > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> >
> > > @@ -1453,10 +1501,16 @@ proc rescan {after {honor_trustmtime 1}} {
> > >  	global HEAD PARENT MERGE_HEAD commit_type
> > >  	global ui_index ui_workdir ui_comm
> > >  	global rescan_active file_states
> > > -	global repo_config
> > > +	global repo_config _gitdir_cache
> > >
> > >  	if {$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}
Johannes Schindelin Oct. 13, 2019, 10:18 p.m. UTC | #4
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).

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 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
>
>
Johannes Schindelin Oct. 14, 2019, 8:14 a.m. UTC | #5
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 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.

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 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]
> > > >  		&& $newType eq {normal}
>
> --
> Regards,
> Pratyush Yadav
>
Pratyush Yadav Oct. 17, 2019, 6:34 p.m. UTC | #6
On 14/10/19 12:18AM, Johannes Schindelin wrote:
> Hi Pratyush,
> 
> On Mon, 14 Oct 2019, Pratyush Yadav wrote:
> 
> > On 12/10/19 11:24PM, Johannes Schindelin wrote:
> > > Hi Pratyush,
> > >
> > > On Sat, 12 Oct 2019, Pratyush Yadav wrote:
> > >
> > > > On 08/10/19 04:33AM, Johannes Schindelin via GitGitGadget wrote:
> > > >
> > > > > @@ -1453,10 +1501,16 @@ proc rescan {after {honor_trustmtime 1}} {
> > > > >  	global HEAD PARENT MERGE_HEAD commit_type
> > > > >  	global ui_index ui_workdir ui_comm
> > > > >  	global rescan_active file_states
> > > > > -	global repo_config
> > > > > +	global repo_config _gitdir_cache
> > > > >
> > > > >  	if {$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`.

Patch
diff mbox series

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
@@ -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}