Re: 3.1.6-test-1: strange cd behaviour

["Bart Schaefer" <schaefer@candle.brasslantern.com>]

On Jul 14, 11:15am, Peter Stephenson wrote:
} Subject: Re: 3.1.6-test-1: strange cd behaviour
}
} > It worked (and still works) in 3.0.  What changed?
} 
} 3.0 relative paths are handled differently from absolute ones, while in 3.1
} the existing pwd is tacked on the front and all are handled together.  In
} 3.0, to make this work, ..'s behave differently if they are going up
} further than the start of the current pwd.  In the case of `cd dummy/..',
} it didn't and instead performed a chdir() on the whole thing, so that was
} tested properly.  On the other hand, cd .. works by examining and
} modifiying the current pwd, so you could cd from a non-existent directory.

Even with chaselinks set?  That would seem to me to be a bug.  And indeed
(in raw 3.0.5, but 3.0.6-pre-5 and 3.1.6-test-1 are the same):

zagzig[24] mkdir /tmp/bar /tmp/foo
zagzig[25] mkdir /tmp/bar/subdir
zagzig[26] cd /tmp/foo
zagzig[27] ln -s /tmp/bar/subdir .
zagzig[28] cd subdir
zagzig[29] setopt chaselinks
zagzig[30] cd ..
zagzig[31] pwd
/tmp/foo

} 3.1 is more integrated: it takes a complete path and operates on that.
} This has the effects previously reported.  Without restoring the 3.0
} behaviour, the fix would be
} 
} - If $PWD is a prefix, rationalize away any immediately following ..'s
}   (and .'s, to be on the safe side) before doing any testing.

So my first suggestion is that no rationalization should happen when
chaselinks is set.

} - At that point, even if $PWD is a prefix, look at the path and see if it
}   contains any /../ or finishes with /.. . If so, stat() it and check
}   that it exists.  If not, return and let the chdir code handle errors.

When chaselinks is NOT set, this approach mail fail due to permissions on
intermediate path elements when in fact it would succeed if the path were
rationalized first.  On the other hand, I suppose that if you want it to
fail because of nonexistent directories you probably want it to fail for
permissions as well.

However, it's also that case that you can't test the entire path once
and then assume it's OK to rationalize it, because stat() will follow
intermediate symlinks whereas rationalization will not.  (You pointed
this out yourself in the message excerpted below.)

As a third point, the correct way to test every component would in at
least some case be to actually chdir() there, not to stat() it.

} - If everything's OK so far (i.e. no ..'s, or the directory exists)
}   rationalize the rest of the path.

On Jul 15,  2:23pm, Peter Stephenson wrote:
} Subject: Re: PATCH: 3.1.6-test-1: strange cd behaviour
}
} "Andrej Borsenkow" wrote:
} > Yes. Completely remove this. If current dir no more exists, the
} > error message here is more of a feature - it indicates, that
} > somethig went wrong.
} 
} Actually, that's not completely removing it, that's including about half
} the code, just not the stuff that allows the PWD to be backtracked
} automatically.  (Unless you are suggesting going back to not testing for a
} non-existent directory at all?  But then you don't get the error message
} with `cd ..'.)

Here's what I propose, in more detail:

(1) When chaselinks is set, don't rationalize, simply attempt the cd and
either get the new directory if it succeeds or issue an error if it fails.
I'm going to peer at 3.0.6-pre; hopefully it isn't too hard to add this
one bit.

(2) When chaselinks is not set, either:
(2a) keep the pre-7139 behavior, or
(2b) add a "chasedots" option or some such that means zsh should act as
though chaselinks is set iff the path contains ".." anywhere.

} Furthermore, whether PWD is a prefix of the *physical* current directory is
} a different issue entirely, depending on the option CHASELINKS.  Without
} that set, zsh will always try to turn $PWD/.. into ${PWD:h}, wherever that
} lands you up.

I just tried this in pre-7139 3.1.6-test-1, and found that zsh *always*
turns $PWD/.. into $PWD:h, completely independent of chaselinks.

zagzig% pwd       
/tmp/foo/subdir
zagzig% setopt chaselinks
zagzig% echo $PWD
/tmp/foo/subdir
zagzig% pwd
/tmp/bar/subdir
zagzig% echo $PWD
/tmp/foo/subdir
zagzig% cd $PWD/..
zagzig% pwd
/tmp/foo

} Which opens another kettle of fish: if the .. is not at the end, then
} /foo/bar/../rod might not be the same physical path as /foo/rod.

Yes, that's the same point I made above about stat().

} (Although with AUTOCD `../rod' on its own already fails,
} because it tests for a physical directory, since cancd() doesn't call
} fixdir() --- anyone want that fixed?)

Only if you add the "chasedots" option.

} Maybe this is already going too far when CHASELINKS is unset.  (I could
} change it to stat every occurrence of <dir>/.. , which was my first
} thought, and which should get round this.)

This is definitely going too far.

} I would be perfectly happy to back off the patch altogether, too.

That plus (1) above would make me comfortable.

-- 
Bart Schaefer                                 Brass Lantern Enterprises
http://www.well.com/user/barts              http://www.brasslantern.com