[ruby/irb] Avoid loading files' local variables [Bug #17623]

https://github.com/ruby/irb/commit/b12f0cb8e2

lib/irb/workspace.rb

@@ -57,6 +57,8 @@ EOF
                           __FILE__,
                           __LINE__ - 3)
         when 4  # binding is a copy of TOPLEVEL_BINDING (default)
+          # Note that this will typically be IRB::TOPLEVEL_BINDING (see exe/irb)
+          # This is to avoid RubyGems' local variables (see issue #17623)
           @binding = TOPLEVEL_BINDING.dup
         end
       end

libexec/irb

@@ -8,4 +8,5 @@
 
 require "irb"
 
+IRB::TOPLEVEL_BINDING = binding
 IRB.start(__FILE__)

test/irb/test_workspace.rb

@@ -80,6 +80,16 @@ module TestIRB
       assert_equal(nil, workspace.code_around_binding)
     end
 
+
+    def test_toplevel_binding_local_variables
+      bug17623 = '[ruby-core:102468]'
+      bundle_exec = ENV.key?('BUNDLE_GEMFILE') ? ['-rbundler/setup'] : []
+      status = assert_in_out_err(bundle_exec + ['-W0', '-e', <<~RUBY , '--', '-f', '--'], 'binding.local_variables', /\[:_\]/, [], bug17623)
+        version = 'xyz' # typical rubygems loading file
+        load('./exe/irb')
+      RUBY
+    end
+
     private
 
     def with_script_lines