Soft link in 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)

Norvell

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 <[email protected]>
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 <[email protected]>
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

Ancillary

You mean it will handle NIX soft links in the files it is versioning? – Norvell

Thanks for the update @chris-wesseling They asked about soft/sym links, but having ht hardlink info is good too. – Ancillary

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

Thermoelectricity

Symbolic links to absolute paths can be added to a mercurial repo. I don't know what "empty paths" means in this context. – Mycology