# HG changeset patch
# User Yuya Nishihara <yuya@tcha.org>
# Date 1427124508 -32400
# Node ID 7afaf2566e25eaa5dfcac7ebf9fedf2fe6b393ae
# Parent  179764469754850bcc22d2895c3a6cc0cb8db2b9
revset: add optional offset argument to limit() predicate

It's common for GUI or web frontend to fetch chunk of revisions per batch
size. Previously it was possible only if revisions were sorted by revision
number.

  $ hg log -r 'limit({revspec} & :{last_known}, 101)'

So this patch introduces a general way to retrieve chunk of revisions after
skipping offset revisions.

  $ hg log -r 'limit({revspec}, 100, {last_count})'

This is a dumb implementation. We can optimize it for baseset and spanset
later.

diff -r 179764469754 -r 7afaf2566e25 mercurial/revset.py
--- a/mercurial/revset.py	Mon Oct 12 17:19:22 2015 +0900
+++ b/mercurial/revset.py	Tue Mar 24 00:28:28 2015 +0900
@@ -1284,24 +1284,33 @@
     return subset.filter(matches)
 
 def limit(repo, subset, x):
-    """``limit(set, [n])``
-    First n members of set, defaulting to 1.
+    """``limit(set[, n[, offset]])``
+    First n members of set, defaulting to 1, starting from offset.
     """
-    args = getargsdict(x, 'limit', 'set n')
+    args = getargsdict(x, 'limit', 'set n offset')
     if 'set' not in args:
         # i18n: "limit" is a keyword
-        raise error.ParseError(_("limit requires one or two arguments"))
+        raise error.ParseError(_("limit requires one to three arguments"))
     try:
-        lim = 1
+        lim, ofs = 1, 0
         if 'n' in args:
             # i18n: "limit" is a keyword
             lim = int(getstring(args['n'], _("limit requires a number")))
+        if 'offset' in args:
+            # i18n: "limit" is a keyword
+            ofs = int(getstring(args['offset'], _("limit requires a number")))
+        if ofs < 0:
+            raise error.ParseError(_("negative offset"))
     except (TypeError, ValueError):
         # i18n: "limit" is a keyword
         raise error.ParseError(_("limit expects a number"))
     os = getset(repo, fullreposet(repo), args['set'])
     result = []
     it = iter(os)
+    for x in xrange(ofs):
+        y = next(it, None)
+        if y is None:
+            break
     for x in xrange(lim):
         y = next(it, None)
         if y is None:
diff -r 179764469754 -r 7afaf2566e25 tests/test-revset.t
--- a/tests/test-revset.t	Mon Oct 12 17:19:22 2015 +0900
+++ b/tests/test-revset.t	Tue Mar 24 00:28:28 2015 +0900
@@ -566,6 +566,16 @@
   $ log 'keyword("test a")'
   $ log 'limit(head(), 1)'
   0
+  $ log 'limit(author("re:bob|test"), 3, 5)'
+  5
+  6
+  7
+  $ log 'limit(author("re:bob|test"), offset=6)'
+  6
+  $ log 'limit(author("re:bob|test"), offset=10)'
+  $ log 'limit(all(), 1, -1)'
+  hg: parse error: negative offset
+  [255]
   $ log 'matching(6)'
   6
   $ log 'matching(6:7, "phase parents user date branch summary files description substate")'