Re: [PATCH 1/2] subtree: fix the GIT_EXEC_PATH sanity check to work on Windows

From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Luke Shumaker <lukeshu@lukeshu.com>
Cc: Johannes Schindelin via GitGitGadget <gitgitgadget@gmail.com>,
	git@vger.kernel.org, Luke Shumaker <lukeshu@datawire.io>
Subject: Re: [PATCH 1/2] subtree: fix the GIT_EXEC_PATH sanity check to work on Windows
Date: Fri, 11 Jun 2021 12:19:17 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.2106111213050.57@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <87bl8d6xoq.wl-lukeshu@lukeshu.com>

Hi Luke,

On Thu, 10 Jun 2021, Luke Shumaker wrote:

> On Thu, 10 Jun 2021 03:13:30 -0600,
> Johannes Schindelin via GitGitGadget wrote:
> >
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > In 22d550749361 (subtree: don't fuss with PATH, 2021-04-27), `git
> > subtree` was broken thoroughly on Windows.
> >
> > The reason is that it assumes Unix semantics, where `PATH` is
> > colon-separated, and it assumes that `$GIT_EXEC_PATH:` is a verbatim
> > prefix of `$PATH`. Neither are true, the latter in particular because
> > `GIT_EXEC_PATH` is a Windows-style path, while `PATH` is a Unix-style
> > path list.
> >
> > Let's keep the original spirit, and hack together something that
> > unbreaks the logic on Windows.
> >
> > A more thorough fix would look at the inode of `$GIT_EXEC_PATH` and of
> > the first component of `$PATH`, to make sure that they are identical,
> > but that is even trickier to do in a portable way.
> >
> > This fixes https://github.com/git-for-windows/git/issues/3260
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  contrib/subtree/git-subtree.sh | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/contrib/subtree/git-subtree.sh b/contrib/subtree/git-subtree.sh
> > index b06782bc7955..6bd689a6bb92 100755
> > --- a/contrib/subtree/git-subtree.sh
> > +++ b/contrib/subtree/git-subtree.sh
> > @@ -5,7 +5,13 @@
> >  # Copyright (C) 2009 Avery Pennarun <apenwarr@gmail.com>
> >  #
> >
> > -if test -z "$GIT_EXEC_PATH" || test "${PATH#"${GIT_EXEC_PATH}:"}" = "$PATH" || ! test -f "$GIT_EXEC_PATH/git-sh-setup"
> > +if test -z "$GIT_EXEC_PATH" || {
> > +	test "${PATH#"${GIT_EXEC_PATH}:"}" = "$PATH" && {
> > +		# On Windows, PATH might be Unix-style, GIT_EXEC_PATH not
> > +		! type -p cygpath >/dev/null 2>&1 ||
> > +		test "${PATH#$(cygpath -au "$GIT_EXEC_PATH"):}" = "$PATH"
>
> Nit: That should have a couple more `"` in it:
>
>     test "${PATH#"$(cygpath -au "$GIT_EXEC_PATH"):"}" = "$PATH"

Are you sure about that?

	$ P='*:hello'; echo "${P#$(echo '*'):}"
	hello

As you can see, there is no problem with that `echo '*'` producing a
wildcard character.

In any case, neither '*' nor '?' are valid filename characters on Windows,
therefore there is little danger here.

To be honest, I was looking more for reviews focusing on
potentially-better solutions, such as looking at the inodes, or even
comparing the contents of `$GIT_EXEC_PATH/git-subtree` and
`${PATH%%:*}/git-subtree`, and complaining if they're not identical.

Those two ideas look a bit ham-handed to me, though, the latter because it
reads the file twice, for _every_ `git subtree` invocation, and the fomer
because there simply is no easy portable way to look at the inode of a
file (stat(1) has different semantics depending whether it is the GNU or
the BSD flavor, and it might not even be present to begin with).

I was also looking forward to hear whether there are opinions about maybe
dropping this check altogether because there were indications that this
condition is not even common anymore.

> But no need to re-roll for just that.
>
> Do we also need to handle the reverse case, where PATH uses
> backslashes but GIT_EXEC_PATH uses forward slashes?

In Git for Windows, we ensure to use forward slashes in `GIT_EXEC_PATH`.

Ciao,
Dscho