Re: [PATCH v3 1/1] Fix gitdir e.g. to respect core.hooksPath

From: Pratyush Yadav <me@yadavpratyush.com>
To: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, Bert Wesarg <bert.wesarg@googlemail.com>,
	Johannes Schindelin <johannes.schindelin@gmx.de>,
	Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH v3 1/1] Fix gitdir e.g. to respect core.hooksPath
Date: Tue, 8 Oct 2019 05:59:02 +0530	[thread overview]
Message-ID: <20191008002902.n4b3bhlvwzsxodsc@yadavpratyush.com> (raw)
In-Reply-To: <65c2fa33e1aeec03930921ee0ef562d3f9dc5ccf.1570225311.git.gitgitgadget@gmail.com>

Hi Johannes,

Could you please change the commit subject to more clearly state that we 
are caching all paths. This is not something just related to hooks any 
more.

On 04/10/19 02:41PM, 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.
> 
> 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 the known entries.

I think it would also be a good idea to mention that we are fixing 
worktree paths not being correct.

> 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 | 52 +++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 49 insertions(+), 3 deletions(-)
> 
> diff --git a/git-gui.sh b/git-gui.sh
> index fd476b6999..8b72e59cd0 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 +198,57 @@ 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} {

I think we should mention the source of the list of "magic" keys. A 
comment mentioning this list came from looking at the common calls to 
`gitdir` in the rest of the git-gui code would explain this function to 
a future reader better.

> +		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"] {

A call to the procedure 'git' is wrapped in a 'catch' in a lot of 
places. But it is also not wrapped in 'catch' in a lot of other places.

I'm not sure how something like this would fail, so I'm not sure if 
wrapping this call in a catch is a good idea. But it is something to 
consider.

> +		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 +1288,7 @@ 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

Can these paths we cache change while git-gui is running, say by a 
command run by the user in the terminal? In that case, we should refresh 
the list when the user rescans.

Other than some minor comments, looks good. Thanks.

-- 
Regards,
Pratyush Yadav