changeset 22449:da05fe01170b

revset: make descendants() lazier

Previously descendants() would force the provided subset to become a set.  In
the case of revsets like '(%ld::) - (%ld)' (as used by histedit) this would
force the '- (%ld)' set to be evaluated, which produced a set containing every
commit in the repo (except %ld). This takes 0.6s on large repos.

This changes descendants to trust the subset to implement __contains__
efficiently, which improves the above revset to 0.16s. Shaving 0.4 seconds off
of histedit.

revset #27: (20000::) - (20000)
0) obsolete feature not enabled but 54243 markers found!
! wall 0.023640 comb 0.020000 user 0.020000 sys 0.000000 (best of 100)
1) obsolete feature not enabled but 54243 markers found!
! wall 0.019589 comb 0.020000 user 0.020000 sys 0.000000 (best of 100)

This commit removes the final revset related perf hotspot from histedit.
Combined with the previous two patches, they shave a little over 3 seconds off
histedit on large repos.

--- a/contrib/revsetbenchmarks.txt	Wed Sep 17 00:28:37 2014 +0900
+++ b/contrib/revsetbenchmarks.txt	Fri Sep 12 16:21:13 2014 -0700
@@ -23,3 +23,4 @@
 max(::(tip~20) - obsolete())
 roots((0:tip)::)
 (not public() - obsolete())
+(20000::) - (20000)

--- a/mercurial/revset.py	Wed Sep 17 00:28:37 2014 +0900
+++ b/mercurial/revset.py	Fri Sep 12 16:21:13 2014 -0700
@@ -666,10 +666,8 @@
     # 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))
+    result = (orderedlazyset(s, subset.__contains__, ascending=True) +
+              orderedlazyset(args, subset.__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.