--- a/mercurial/patch.py	Thu Oct 15 23:15:30 2009 +0200
+++ b/mercurial/patch.py	Thu Oct 15 23:15:30 2009 +0200
@@ -301,7 +301,14 @@
             fp.close()
 
     def writelines(self, fname, lines):        
-        fp = self.opener(fname, 'w')
+        # Ensure supplied data ends in fname, being a regular file or
+        # a symlink. updatedir() will -too magically- take care of
+        # setting it to the proper type afterwards.
+        islink = os.path.islink(fname)
+        if islink:
+            fp = cStringIO.StringIO()
+        else:
+            fp = self.opener(fname, 'w')
         try:
             if self.eol and self.eol != '\n':
                 for l in lines:
@@ -310,6 +317,8 @@
                     fp.write(l)
             else:
                 fp.writelines(lines)
+            if islink:
+                self.opener.symlink(fp.getvalue(), fname)
         finally:
             fp.close()
 

--- a/tests/test-mq-symlinks	Thu Oct 15 23:15:30 2009 +0200
+++ b/tests/test-mq-symlinks	Thu Oct 15 23:15:30 2009 +0200
@@ -10,7 +10,8 @@
 hg qnew base.patch
 echo aaa > a
 echo bbb > b
-hg add a b
+echo ccc > c
+hg add a b c
 hg qrefresh
 $TESTDIR/readlink.py a
 
@@ -25,6 +26,28 @@
 hg qpush
 $TESTDIR/readlink.py a
 
+echo '% test updating a symlink'
+rm a
+ln -s c a
+hg qnew --git -f updatelink
+$TESTDIR/readlink.py a
+hg qpop
+hg qpush --debug
+$TESTDIR/readlink.py a
+hg st
+
+echo '% test replacing a symlink with a file'
+ln -s c s
+hg add s
+hg qnew --git -f addlink
+rm s
+echo sss > s
+hg qnew --git -f replacelinkwithfile
+hg qpop
+hg qpush
+cat s
+hg st
+
 echo '% test symlink removal' 
 hg qnew removesl.patch
 hg rm a

--- a/tests/test-mq-symlinks.out	Thu Oct 15 23:15:30 2009 +0200
+++ b/tests/test-mq-symlinks.out	Thu Oct 15 23:15:30 2009 +0200
@@ -5,8 +5,23 @@
 applying symlink.patch
 now at: symlink.patch
 a -> b
+% test updating a symlink
+a -> c
+now at: symlink.patch
+applying updatelink
+patching file a
+a
+now at: updatelink
+a -> c
+% test replacing a symlink with a file
+now at: addlink
+applying replacelinkwithfile
+now at: replacelinkwithfile
+sss
 % test symlink removal
-now at: symlink.patch
+now at: replacelinkwithfile
 applying removesl.patch
 now at: removesl.patch
 C b
+C c
+C s