Bail out of reducing depency trees on huge dependency conflict sets

This is a simple fix for #6114, in which sometimes conflict sets get so huge that
the current reducing code (which is based on Array#combination) breaks down.

By simply bailing out when the conflict set is bigger than a certain size,
we'll get a result that is similar to what happened in earlier bundler versions
but skip a ton of CPU cycles and memory allocations.

I've chosen the limit rather unscientifically by playing around with the result
set sizes. 15 seems to be a good compromise but really anything larger than 10
should work (and with work I mean "should not usually not have to be invoked").

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/bundler/resolver.rb b/lib/bundler/resolver.rb
index f75c669534..8a3afa3418 100644
--- a/lib/bundler/resolver.rb
+++ b/lib/bundler/resolver.rb
@@ -309,6 +309,8 @@ module Bundler
         :solver_name => "Bundler",
         :possibility_type => "gem",
         :reduce_trees => lambda do |trees|
+          # bail out if tree size is too big for Array#combination to make any sense
+          return trees if trees.size > 15
           maximal = 1.upto(trees.size).map do |size|
             trees.map(&:last).flatten(1).combination(size).to_a
           end.flatten(1).select do |deps|