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

[Luke Shumaker <lukeshu@lukeshu.com>]

On Fri, 11 Jun 2021 04:19:17 -0600,
Johannes Schindelin wrote:
> 
> Hi Luke,
> 
> 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

> 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.

> 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.

-- 
Happy hacking,
~ Luke Shumaker