# HG changeset patch
# User Durham Goode <durham@fb.com>
# Date 1395781801 25200
# Node ID 04e1596d5dbdc7cb14f16c1ed60c22d599cf24de
# Parent  b5de9dde181c2edd30f290713c2db0a289e9f13f
revset: improve _descendants performance

Previously revset._descendants would iterate over the entire subset (which is
often the entire repo) and test if each rev was in the descendants list. This is
really slow on large repos (3+ seconds).

Now we iterate over the descendants and test if they're in the subset.
This affects advancing and retracting the phase boundary (3.5 seconds down to
0.8 seconds, which is even faster than it was in 2.9). Also affects commands
that move the phase boundary (commit and rebase, presumably).

The new revsetbenchmark indicates an improvement from 0.2 to 0.12 seconds. So
future revset changes should be able to notice regressions.

I removed a bad test. It was recently added and tested '1:: and reverse(all())',
which has an amibiguous output direction.  Previously it printed in reverse order,
because we iterated over the subset (the reverse part). Now it prints in normal
order because we iterate over the 1:: . Since the revset itself doesn't imply an
order, I removed the test.

diff -r b5de9dde181c -r 04e1596d5dbd contrib/revsetbenchmarks.txt
--- a/contrib/revsetbenchmarks.txt	Mon Mar 31 16:29:39 2014 -0700
+++ b/contrib/revsetbenchmarks.txt	Tue Mar 25 14:10:01 2014 -0700
@@ -12,4 +12,5 @@
 min(0:tip)
 0::
 min(0::)
+roots((tip~100::) - (tip~100::tip))
 ::p1(p1(tip))::
diff -r b5de9dde181c -r 04e1596d5dbd mercurial/revset.py
--- a/mercurial/revset.py	Mon Mar 31 16:29:39 2014 -0700
+++ b/mercurial/revset.py	Tue Mar 25 14:10:01 2014 -0700
@@ -661,8 +661,18 @@
     if not args:
         return baseset([])
     s = _revdescendants(repo, args, followfirst)
-    a = set(args)
-    return subset.filter(lambda r: r in s or r in a)
+
+    # Both sets need to be ascending in order to lazily return the union
+    # in the correct order.
+    args.ascending()
+
+    subsetset = subset.set()
+    result = (orderedlazyset(s, subsetset.__contains__, ascending=True) +
+              orderedlazyset(args, subsetset.__contains__, ascending=True))
+
+    # Wrap result in a lazyset since it's an _addset, which doesn't implement
+    # all the necessary functions to be consumed by callers.
+    return orderedlazyset(result, lambda r: True, ascending=True)
 
 def descendants(repo, subset, x):
     """``descendants(set)``
diff -r b5de9dde181c -r 04e1596d5dbd tests/test-revset.t
--- a/tests/test-revset.t	Mon Mar 31 16:29:39 2014 -0700
+++ b/tests/test-revset.t	Tue Mar 25 14:10:01 2014 -0700
@@ -474,16 +474,6 @@
   2
   1
   0
-  $ log '1:: and reverse(all())'
-  9
-  8
-  7
-  6
-  5
-  4
-  3
-  2
-  1
   $ log 'rev(5)'
   5
   $ log 'sort(limit(reverse(all()), 3))'