revset: optimize "draft() & ::x" pattern The `draft() & ::x` type query could be common for selecting one or more draft feature branches being worked on. Before this patch, `::x` may travel through the changelog DAG for a long distance until it gets a smaller revision number than `min(draft())`. It could be very slow on long changelog with distant (in terms of revision numbers) drafts. This patch adds a fast path for this situation, and will stop traveling the changelog DAG once `::x` hits a non-draft revision. The fast path also works for `secret()` and `not public()`. To measure the performance difference, I used drawdag to create a repo that emulates distant drafts: DRAFT4 | DRAFT3 # draft / PUBLIC9999 # public | PUBLIC9998 | . DRAFT2 . | . DRAFT1 # draft | / PUBLIC0001 # public And measured the performance using the repo: (BEFORE) $ hg perfrevset 'draft() & ::(DRAFT2+DRAFT4)' ! wall 0.017132 comb 0.010000 user 0.010000 sys 0.000000 (best of 156) $ hg perfrevset 'draft() & ::(all())' ! wall 0.024221 comb 0.030000 user 0.030000 sys 0.000000 (best of 113) (AFTER) $ hg perfrevset 'draft() & ::(DRAFT2+DRAFT4)' ! wall 0.000243 comb 0.000000 user 0.000000 sys 0.000000 (best of 9303) $ hg perfrevset 'draft() & ::(all())' ! wall 0.004319 comb 0.000000 user 0.000000 sys 0.000000 (best of 655) Differential Revision: https://phab.mercurial-scm.org/D441

--- a/mercurial/revsetlang.py	Fri Sep 01 12:13:17 2017 -0700
+++ b/mercurial/revsetlang.py	Mon Aug 28 14:49:00 2017 -0700
@@ -369,6 +369,11 @@
         wb, tb = _optimize(x[2], True)
         w = min(wa, wb)
 
+        # (draft/secret/_notpublic() & ::x) have a fast path
+        m = _match('_() & ancestors(_)', ('and', ta, tb))
+        if m and getsymbol(m[1]) in {'draft', 'secret', '_notpublic'}:
+            return w, _build('_phaseandancestors(_, _)', m[1], m[2])
+
         # (::x and not ::y)/(not ::y and ::x) have a fast path
         m = _matchonly(ta, tb) or _matchonly(tb, ta)
         if m: