--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/hgext3rd/topic/revset.py	Thu Mar 17 09:12:18 2016 -0700
@@ -0,0 +1,50 @@
+from mercurial import revset
+from mercurial import util
+
+from . import constants, destination
+
+try:
+    mkmatcher = revset._stringmatcher
+except AttributeError:
+    mkmatcher = util.stringmatcher
+
+
+def topicset(repo, subset, x):
+    """`topic([topic])`
+    Specified topic or all changes with any topic specified.
+
+    If `topic` starts with `re:` the remainder of the name is treated
+    as a regular expression.
+
+    TODO: make `topic(revset)` work the same as `branch(revset)`.
+    """
+    args = revset.getargs(x, 0, 1, 'topic takes one or no arguments')
+    if args:
+        # match a specific topic
+        topic = revset.getstring(args[0], 'topic() argument must be a string')
+        if topic == '.':
+            topic = repo['.'].extra().get('topic', '')
+        _kind, _pattern, matcher = mkmatcher(topic)
+    else:
+        matcher = lambda t: bool(t)
+    drafts = subset.filter(lambda r: repo[r].mutable())
+    return drafts.filter(
+        lambda r: matcher(repo[r].extra().get(constants.extrakey, '')))
+
+def ngtipset(repo, subset, x):
+    """`ngtip([branch])`
+
+    The untopiced tip.
+
+    Name is horrible so that people change it.
+    """
+    args = revset.getargs(x, 1, 1, 'topic takes one')
+    # match a specific topic
+    branch = revset.getstring(args[0], 'ngtip() argument must be a string')
+    if branch == '.':
+        branch = repo['.'].branch()
+    return subset & destination.ngtip(repo, branch)
+
+def modsetup():
+    revset.symbols.update({'topic': topicset})
+    revset.symbols.update({'ngtip': ngtipset})