symlinked working tree gotcha

symlinked working tree gotcha

[Joey Hess]

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joey@gnu:/tmp>mkdir foo
joey@gnu:/tmp>cd foo
joey@gnu:/tmp/foo>git init
Initialized empty Git repository in /tmp/foo/.git/
joey@gnu:/tmp/foo>touch foo
joey@gnu:/tmp/foo>git add /tmp/foo/foo
joey@gnu:/tmp/foo>cd ..
joey@gnu:/tmp>ln -s foo bar
joey@gnu:/tmp>cd bar
joey@gnu:/tmp/bar>touch bar
joey@gnu:/tmp/bar>git add /tmp/bar/bar
fatal: '/tmp/bar/bar' is outside repository

Is this a bug or a feature of git? I had some code where I had, lazily,
assumed that passing the full path to the file would always work, since
it did, in my experience.

-- 
see shy jo

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Re: symlinked working tree gotcha

[Junio C Hamano]

Joey Hess <joey@kitenet.net> writes:

> joey@gnu:/tmp>mkdir foo
> joey@gnu:/tmp>cd foo
> joey@gnu:/tmp/foo>git init
> Initialized empty Git repository in /tmp/foo/.git/
> joey@gnu:/tmp/foo>touch foo
> joey@gnu:/tmp/foo>git add /tmp/foo/foo
> joey@gnu:/tmp/foo>cd ..
> joey@gnu:/tmp>ln -s foo bar
> joey@gnu:/tmp>cd bar
> joey@gnu:/tmp/bar>touch bar
> joey@gnu:/tmp/bar>git add /tmp/bar/bar
> fatal: '/tmp/bar/bar' is outside repository
>
> Is this a bug or a feature of git?

Two 'foo's makes it confusing to read so let's rephrase.

Given this structure:

    /tmp/foo/
    /tmp/foo/.git/
    /tmp/foo/hello
    /tmp/sym@ -> foo

when you refer to /tmp/sym/hello where $(/bin/pwd) is /tmp/foo, should it
be considered to be within the bounds of the working tree that is governed
by your current $GIT_DIR (which is ".git")?

The answer is "perhaps yes, ideally speaking, but does it really matter in
practice, or is it just nice to have?".

I think we do not run realpath to a pathspec given by the end user to
canonicalize it.  And we cannot blindly run realpath.

Think of this structure (the above with some additions):

    /tmp/foo/
    /tmp/foo/.git/
    /tmp/foo/hello
    /tmp/foo/dir/bye
    /tmp/foo/link@ -> dir
    /tmp/sym@ -> foo

and you refer to /tmp/sym/link/bye from /tmp/foo directory.  If we run
realpath to the whole thing, we would get /tmp/foo/dir/bye but as far as
the repository data is concerned, link/bye is beyond a tracked symbolic
link and we should error it out ("git add link/bye" should fail).

If we choose to make your example work, we would need to resolve symbolic
links stepwise until we get into the working tree, and then use the
remainder without resolving symbolic links, e.g.

 0. We get /tmp/sym/hello  and /tmp/sym/link/bye from the user;

 1. Notice /tmp is a directory and outside the working tree;

 2. Notice /tmp/sym is a symlink; resolve it to get /tmp/foo, notice
    that directory is now within the working tree, and stop resolving
    symbolic links for the remainder;

 3. Append the remainder to come up with /tmp/foo/hello and
   /tmp/foo/link/bye;

 4. Strip /tmp/foo/, to get hello and link/bye as pathspec relative to the
    root of the working tree;

 5. Use them as the pathspec. hello is a valid pathspec within the working
    tree. link/bye is beyond symlink and an error should be reported.

Or something like that.  We would also have to deal with "../" in the
pathspec, so we cannot just "stop resolving and tack the remainder", but
would probably need to check if the directory is within bounds of the
working tree in each step.

At least I would say it would be a sensible thing to aim for.

Re: symlinked working tree gotcha

[Joey Hess]

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Junio C Hamano wrote:
> Two 'foo's makes it confusing to read so let's rephrase.
> 
> Given this structure:
> 
>     /tmp/foo/
>     /tmp/foo/.git/
>     /tmp/foo/hello
>     /tmp/sym@ -> foo
> 
> when you refer to /tmp/sym/hello where $(/bin/pwd) is /tmp/foo, should it
> be considered to be within the bounds of the working tree that is governed
> by your current $GIT_DIR (which is ".git")?

Hmm, my /bin/pwd does not return "/tmp/foo" when I've cd'd to "/tmp/sym".

> The answer is "perhaps yes, ideally speaking, but does it really matter in
> practice, or is it just nice to have?".

FWIW, my motivation for using the absolute path was that I wanted to
always add $GIT_WORK_TREE/hello, but the add could be run when in a
subdirectory of the repository, so "git add hello" might not add the
right file.

-- 
see shy jo

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Re: symlinked working tree gotcha

[Jay Soffian]

On Mon, Apr 25, 2011 at 3:09 PM, Joey Hess <joey@kitenet.net> wrote:
> Hmm, my /bin/pwd does not return "/tmp/foo" when I've cd'd to "/tmp/sym".

A pwd misfeature IMO. Try:

$ pwd -P

You can make -P the default in bash with "shopt -s -o physical"

j.