#46 Tclvfs interferes witn OS-level links outside vfs space

[Stephen Huntley]

On Windows, if "file link" is used to create a link
from a location outside vfs space to a location that is
real but referenced by a virtual filesystem, the glob
and file commands give inconsistent results as to
whether the relevant vfs handler code is accessed.

To reproduce:

create two real directories:

% file mkdir C:/temp/test
% file mkdir C:/temp/vfs

create a unique file in each directory:

% close [open C:/temp/test/test.txt w]
% close [open C:/temp/vfs/vfs.txt w]

create an OS-level link to the real directory "test":

% file link C:/temp/link C:/temp/test

verify that this link shows the contents of "test":

% glob -dir C:/temp/link *
C:/temp/link/test.txt
% file exists C:/temp/link/test.txt
1

The attached file contains a virtual file system that
simply mirrors one directory to another. In this case,
the mount point of the vfs will be the same as the real
directory C:/temp/test, making it a virtual location
that mirrors C:/temp/vfs.

% source templatevfs.tcl
% vfs::template::Mount C:/temp/vfs C:/temp/test

verify that C:/temp/test now mirrors C:/temp/vfs:

% glob -dir C:/temp/test *
C:/temp/test/vfs.txt
% file exists C:/temp/test/vfs.txt
1

but now notice the behavior of C:/temp/link has changed:

% glob -dir C:/temp/link *
C:/temp/link/test.txt
% file exists /temp/link/test.txt
0
% file exists /temp/link/vfs.txt
1

The glob command works as before, but other file
functions for some reason trigger Tclvfs and cause the
vfs handler to be called on the location to which
C:/temp/link is linked.

As far as I can see, there is no reason why Tclvfs
should involve itself in file commands accessing the
linked location. Linking is an OS-level activity, only
the operating system should know that C:/temp/link is
the same as C:/temp/test. The file commands should be
able to access the link cleanly without Tclvfs ever
becoming involved.

The fact that glob and file act differently leads me to
conclude that there's a bug here somewhere, no matter
how you slice it.

[Stephen Huntley]

Template vfs code