Check that #require was redefined by RubyGems

* If not, we would end up in infinite recursion, so better fail fast.

(cherry picked from commit 36b8a53)

Author: eregon

lib/truffle/truffle/lazy-rubygems.rb

@@ -10,6 +10,9 @@
 # Otherwise, --disable-gems would degrade startup which is counter-intuitive.
 Truffle::Boot.delay do
   if Truffle::Boot.get_option 'rubygems'
+    module Truffle::LazyRubyGems
+    end
+
     module Kernel
       # Take this alias name so RubyGems will reuse this copy
       # and skip the method below once RubyGems is loaded.
@@ -20,10 +23,18 @@ module Kernel
           gem_original_require(path)
         rescue LoadError
           gem_original_require 'rubygems'
-          require path
+
+          # Check that #require was redefined by RubyGems, otherwise we would end up in infinite recursion
+          new_require = ::Kernel.instance_method(:require)
+          if new_require == Truffle::LazyRubyGems::LAZY_REQUIRE
+            raise 'RubyGems did not redefine #require as expected, make sure $LOAD_PATH and home are set correctly'
+          end
+          new_require.bind(self).call(path)
         end
       end
 
+      Truffle::LazyRubyGems::LAZY_REQUIRE = instance_method(:require)
+
       private def gem(*args)
         require 'rubygems'
         gem(*args)