use .extend instead of .append in readtags

mercurial/localrepo.py

@@ -307,7 +307,7 b' class localrepository(repo.repository):'
                 if bn != an and an in bh and \
                    (bn not in ah or len(bh) > len(ah)):
                     an = bn
-                ah.append([n for n in bh if n not in ah])
+                ah.extend([n for n in bh if n not in ah])
                 globaltags[k] = an, ah
 
         # read the tags file from each head, ending with the tip

tests/test-tags

@@ -104,4 +104,21 b" hg ci -m 'change foo' -d '1000000 0' "
 hg tags
 
 hg tag -d '1000000 0' -r 3 bar         # should complain
-hg tags
  No newline at end of file
+hg tags
+
+# test tag rank with 3 heads
+cd ..
+hg init t4
+cd t4
+echo foo > foo
+hg add
+hg ci -m 'add foo' -d '0 0'                # rev 0
+hg tag -d '0 0' bar                        # rev 1 bar -> 0
+hg tag -d '0 0' -f bar                     # rev 2 bar -> 1
+hg up -qC 0
+hg tag -d '0 0' -fr 2 bar                  # rev 3 bar -> 2
+hg tags
+hg up -qC 0
+hg tag -d '0 0' -m 'retag rev 0' -fr 0 bar # rev 4 bar -> 0, but bar stays at 2
+echo % bar should still point to rev 2
+hg tags

tests/test-tags.out

@@ -57,3 +57,9 b' bar 0:b40'
 abort: a tag named bar already exists (use -f to force)
 tip                                6:b5ff9d142648
 bar                                0:b409d9da318e
+adding foo
+tip                                3:ca8479b4351c
+bar                                2:72b852876a42
+% bar should still point to rev 2
+tip                                4:40af5d225513
+bar                                2:72b852876a42