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

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Luke,

On Fri, 11 Jun 2021, Luke Shumaker wrote:

> On Fri, 11 Jun 2021 04:19:17 -0600,
> Johannes Schindelin wrote:
> >
> > On Thu, 10 Jun 2021, Luke Shumaker wrote:
> >
> > > On Thu, 10 Jun 2021 03:13:30 -0600,
> > > Johannes Schindelin via GitGitGadget wrote:
> > > > -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.
>
> In the other email (the reply to Junio), I specified that it's only a
> problem if the glob isn't self-matching.  So * and ? are fine, but
> [charset] probably isn't.
>
>     $ P='f[o]o:bar'; echo "${P#$(echo 'f[o]o'):}"
>     f[o]o:bar
>
>     $ P='f[o]o:bar'; echo "${P#"$(echo 'f[o]o'):"}"
>     bar

Thank you for clarifying.

This is actually a valid concern also on Windows because according to
https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file the
brackets _are_ valid file name characters.

> > 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.
>
> So the check right now is gross, but I don't know what would be
> better.  The point of the check is more to check "is the environment
> set up the way that `git` sets it up for us", not so much to actually
> check the filesystem.
>
> Plus, it shouldn't actually care if it's installed in `$GIT_EXEC_PATH`
> or not, it should be totally happy for $GIT_EXEC_PATH/git-subtree to
> not exist and for git-subtree to be elsewhere in the PATH.  So an
> inode or content check would be wrong.  Perhaps checking git-sh-setup
> instead of git-subtree though...
>
> > 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).
>
> `test FILE1 -ef FILE2` checks wether the inode is the same.  And it's
> POSIX, so I'm assuming that it's sufficiently portable, though I
> haven't actually tested whether things other than Bash implement it.

It's not POSIX. From
https://pubs.opengroup.org/onlinepubs/009695399/utilities/test.html:

	Some additional primaries newly invented or from the KornShell
	appeared in an early proposal as part of the conditional command
	([[]]): s1 > s2, s1 < s2, str = pattern, str != pattern,
	f1 -nt f2, f1 -ot f2, and f1 -ef f2.

Having said that, it appears that Bash implements it (what non-standard
behavior _doesn't_ it implement ;-))

And since Git for Windows ships with Bash, we can actually use it!

> > 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.
>
> I think it would be good for it to eventually go away.  But having
> removed the hacks that allowed it to work in broken setups, I have no
> way of knowing how many people had setups like that unless they tell
> me now that it's telling them, and if those users are now broken, I
> don't want them to be *silently* broken.  So I think we do need to
> have the check for a longish period of time.
>
> > > 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`.
>
> Did you mean to write `PATH` here instead of `GIT_EXEC_PATH`?  Because
> if not, then I'm confused.

Ah, I thought it was clear that the `PATH` variable is already _not_ the
standard Windows version (which contains backslashes and _semicolons_),
but it is adjusted automatically by the MSYS2 runtime to look more
Unix-like (with forward slashes and _colons_).

Ciao,
Dscho