util: enable hardlink for copyfile

This patch removes the global variable "allowhardlinks" that disables
hardlink in all cases, so hardlink gets enabled if the filesystem type is
whitelisted.

Third party extensions wanting to enable hardlink support unconditionally
can replace "_hardlinkfswhitelist.__contains__".

mercurial/util.py

@@ -1055,11 +1055,6 b' def checksignature(func):'
 
     return check
 
-# Hardlinks are problematic on CIFS, do not allow hardlinks
-# until we find a way to work around it cleanly (issue4546).
-# This is a variable so extensions can opt-in to using them.
-allowhardlinks = False
-
 # a whilelist of known filesystems where hardlink works reliably
 _hardlinkfswhitelist = set([
     'btrfs',
@@ -1095,7 +1090,7 b' def copyfile(src, dest, hardlink=False, '
         fstype = getattr(osutil, 'getfstype', lambda x: None)(destdir)
         if fstype not in _hardlinkfswhitelist:
             hardlink = False
-    if allowhardlinks and hardlink:
+    if hardlink:
         try:
             oslink(src, dest)
             return

tests/test-hardlinks-whitelisted.t

@@ -1,4 +1,10 b''
 #require hardlink
+#require hardlink-whitelisted
+
+This test is similar to test-hardlinks.t, but will only run on some filesystems
+that we are sure to have known good hardlink supports (see issue4546 for an
+example where the filesystem claims hardlink support but is actually
+problematic).
 
   $ cat > nlinks.py <<EOF
   > import sys
@@ -166,7 +172,7 b' Push to repo r1 should break up most har'
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   2 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  2 r2/.hg/store/fncache
 
   $ hg -R r2 verify
   checking changesets
@@ -191,7 +197,7 b' Committing a change to f1 in r1 must bre'
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   1 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  2 r2/.hg/store/fncache
 
 
   $ cd r3
@@ -233,11 +239,11 b' r4 has hardlinks in the working dir (not'
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  4 r4/.hg/undo.backup.dirstate
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  4 r4/.hg/undo.dirstate
   2 r4/d1/data1
   2 r4/d1/f2
   2 r4/f1
@@ -272,11 +278,11 b' Update back to revision 11 in r4 should '
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  4 r4/.hg/undo.backup.dirstate
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  4 r4/.hg/undo.dirstate
   2 r4/d1/data1
   2 r4/d1/f2
   1 r4/f1

tests/test-hardlinks.t

@@ -166,7 +166,7 b' Push to repo r1 should break up most har'
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   2 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  [12] r2/\.hg/store/fncache (re)
 
   $ hg -R r2 verify
   checking changesets
@@ -191,7 +191,7 b' Committing a change to f1 in r1 must bre'
   1 r2/.hg/store/00manifest.i
   1 r2/.hg/store/data/d1/f2.i
   1 r2/.hg/store/data/f1.i
-  1 r2/.hg/store/fncache
+  [12] r2/\.hg/store/fncache (re)
 
 
   $ cd r3
@@ -233,11 +233,11 b' r4 has hardlinks in the working dir (not'
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  [24] r4/\.hg/undo\.backup\.dirstate (re)
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  [24] r4/\.hg/undo\.dirstate (re)
   2 r4/d1/data1
   2 r4/d1/f2
   2 r4/f1
@@ -272,11 +272,11 b' Update back to revision 11 in r4 should '
   2 r4/.hg/store/undo.backup.phaseroots
   2 r4/.hg/store/undo.backupfiles
   2 r4/.hg/store/undo.phaseroots
-  2 r4/.hg/undo.backup.dirstate
+  [24] r4/\.hg/undo\.backup\.dirstate (re)
   2 r4/.hg/undo.bookmarks
   2 r4/.hg/undo.branch
   2 r4/.hg/undo.desc
-  2 r4/.hg/undo.dirstate
+  [24] r4/\.hg/undo\.dirstate (re)
   2 r4/d1/data1
   2 r4/d1/f2
   1 r4/f1