Soft link in Mercurial - mercurial

Question

Is there some equivalent in Mercurial to NIX soft- or hard- links to directories or files.
Basically that a file (or directory) is linked to a file "somewhere else" and follows the version of that location (Unlike a regular branch I think, where one would have to merge)

Answer 1

Mercurial versions soft links that are internal to the repository just great. It'll detect them, record them, and create them for you. Is there a specific use case you're looking for? The closest thing to an link that reaches outside the repository is a subrepo, which is a pointer to a specific version of another repo.
Symlinks work
(df)Ry4ans-MacBook-Air:~ ry4an$ hg init olav
(df)Ry4ans-MacBook-Air:~ ry4an$ cd olav/
(df)Ry4ans-MacBook-Air:olav ry4an$ echo this > target
(df)Ry4ans-MacBook-Air:olav ry4an$ ln -s target link
(df)Ry4ans-MacBook-Air:olav ry4an$ ls -l
total 16
lrwxr-xr-x 1 ry4an staff 6B Feb 16 19:25 link# -> target
-rw-r--r-- 1 ry4an staff 5B Feb 16 19:25 target
(df)Ry4ans-MacBook-Air:olav ry4an$ hg commit -A -m "link and its target"
adding link
adding target
(df)Ry4ans-MacBook-Air:olav ry4an$ hg log -p
changeset: 0:42a41a431661
tag: tip
user: Ry4an Brase <ry4an-hg#ry4an.org>
date: Sat Feb 16 19:26:17 2013 -0500
summary: link and its target
diff -r 000000000000 -r 42a41a431661 link
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/link Sat Feb 16 19:26:17 2013 -0500
## -0,0 +1,1 ##
+target
\ No newline at end of file
diff -r 000000000000 -r 42a41a431661 target
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/target Sat Feb 16 19:26:17 2013 -0500
## -0,0 +1,1 ##
+this
(df)Ry4ans-MacBook-Air:olav ry4an$ hg update null
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
(df)Ry4ans-MacBook-Air:olav ry4an$ ls -l
(df)Ry4ans-MacBook-Air:olav ry4an$ hg update tip
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
(df)Ry4ans-MacBook-Air:olav ry4an$ ls -l
total 16
lrwxr-xr-x 1 ry4an staff 6B Feb 16 19:26 link# -> target
-rw-r--r-- 1 ry4an staff 5B Feb 16 19:26 target
But hardlinks don't
$hg commit -Am "hardlinks target"
adding link
adding target
$hg log -p
changeset: 0:ec9407634133
tag: tip
user: Chris Wesseling <chris.wesseling#cwi.nl>
date: Wed Mar 13 23:14:44 2013 +0100
summary: hardlinks target
diff -r 000000000000 -r ec9407634133 link
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/link Wed Mar 13 23:14:44 2013 +0100
## -0,0 +1,1 ##
+foo
diff -r 000000000000 -r ec9407634133 target
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/target Wed Mar 13 23:14:44 2013 +0100
## -0,0 +1,1 ##
+foo
$ls -lin
total 8
276702 -rw-r--r-- 2 1204653 5900 4 13 mrt 23:14 link
276702 -rw-r--r-- 2 1204653 5900 4 13 mrt 23:14 target
$hg update null
0 files updated, 0 files merged, 2 files removed, 0 files unresolved
$hg update tip
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ls -lin
total 8
276719 -rw-r--r-- 1 1204653 5900 4 13 mrt 23:15 link
276721 -rw-r--r-- 1 1204653 5900 4 13 mrt 23:15 target

Answer 2

Path auditing on *nix
On *nix systems, hg Mercurial audits symbolic links ("symlinks") for referred path security.
For example, absolute and empty paths are considered unsafe and will therefore not be added to the repository.
Mercurial developers have not documented this feature. However, the source code contains a comment with a somewhat vague explanation:
class pathauditor(object):
'''ensure that a filesystem path contains no banned components.
the following properties of a path are checked:
- ends with a directory separator
- under top-level .hg
- starts at the root of a windows drive
- contains ".."
- traverses a symlink (e.g. a/symlink_here/b)
- inside a nested repository (a callback can be used to approve
some nested repositories, e.g., subrepositories)
'''
On Windows, symbolic links are not supported for various reasons, see:
https://www.mercurial-scm.org/bts/issue1825
https://www.mercurial-scm.org/bts/issue2579