Native symbolic links to non-existent targets (possible bug?)

Brian Ericson bericson@ptc.com
Tue Sep 30 06:35:00 GMT 2014


Cygwin appears to ignore "winsymlinks:native" when asked to create a 
symbolic link to a non-existent target, reverting to its "magic header" 
approach.

This can be demonstrated via the following examples (using a Cygwin shell):
   echo hello > aaa
   ln -s aaa bbb
   notepad bbb

   ln -s xxx yyy
   notepad yyy

"notepad bbb" will show "hello", but "notepad yyy" produces "㰡祳汭湩 
㹫xxx ".  "bbb" is a native symbolic link, "yyy" is not.  (This can 
also be confirmed using "dir" (cmd.exe /c dir from within Cygwin) or 
looking for the curved arrow glyph in the folder explorer.)

Note that this is in contrast to mklink (using a command prompt):
   echo hello > aaaa
   mklink bbbb aaaa
   notepad bbbb

   mklink yyyy xxxx
   notepad yyyy

In this case, both mklink commands succeed; "notepad bbbb" works as 
expected, and "notepad yyyy" pops up an alert with "Cannot find the yyyy 
file. Do you want to create a new file?", which makes sense (it even 
writes to xxxx if you say "yes").

Also, mklink-created symbolic links to non-existent targets appear to 
work (just as they do on *nix) when the non-existent target is created:
   echo hello again > xxxx
   notepad yyyy

The result is now "hello again".

I initially stumbled upon this discrepancy in the following real-world 
example:
   git init foo
   cd foo
   touch .gitignore
   git add .gitignore
   git commit -m 'first commit'
   git checkout -b links
   mkdir -p a/b
   echo hello > a/file_in_a
   ln -s ../file_in_a a/b/link_to_file_in_a
   git add a
   git commit -m 'Added symbolic link'

At this point, we have a valid, native symbolic link, which can be 
confirmed using notepad as before:
   notepad a/b/link_to_file_in_a

We run into problems, however, when we do the following:
   git checkout master && git checkout links

Git will create the symbolic link *before* it creates the target, and 
the result is a non-native file.  "notepad a/b/link_to_file_in_a" now 
produces "㰡祳汭湩㹫../file_in_a ".

Shouldn't Cygwin honor "winsymlinks:native" even with the target does 
not exist?

I'm using Cygwin 6.1.

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