Fix rdbg's RUBYOPT handling logic

exe/rdbg

@@ -13,10 +13,10 @@ when :start
   start_mode = config[:remote] ? "open" : 'start'
   cmd = config[:command] ? ARGV.shift : (ENV['RUBY'] || RbConfig.ruby)
 
+  rubyopt = ENV['RUBYOPT']
   env = ::DEBUGGER__::Config.config_to_env_hash(config)
-  rubyopt = env['RUBYOPT']
   env['RUBY_DEBUG_ADDED_RUBYOPT'] = added = "-r #{libpath}/#{start_mode}"
-  env['RUBYOPT'] = "#{added} #{rubyopt}"
+  env['RUBYOPT'] = "#{rubyopt} #{added}"
 
   exec(env, cmd, *ARGV)
 

lib/debug/session.rb

@@ -22,8 +22,9 @@
 # restore RUBYOPT
 if (added_opt = ENV['RUBY_DEBUG_ADDED_RUBYOPT']) &&
    (rubyopt = ENV['RUBYOPT']) &&
-   rubyopt.start_with?(added_opt)
-  ENV['RUBYOPT'] = rubyopt.delete_prefix(rubyopt)
+   rubyopt.end_with?(added_opt)
+
+  ENV['RUBYOPT'] = rubyopt.delete_suffix(added_opt)
   ENV['RUBY_DEBUG_ADDED_RUBYOPT'] = nil
 end
 
@@ -2120,7 +2121,7 @@ def self.load_rc
   end
 
   # Inspector
-  
+
   SHORT_INSPECT_LENGTH = 40
 
   class LimitedPP

test/console/rdbg_option_test.rb

@@ -3,6 +3,31 @@
 require_relative '../support/console_test_case'
 
 module DEBUGGER__
+  class RUBYOPTHandlingTest < ConsoleTestCase
+    def program
+      <<~RUBY
+      1| a = 1
+      RUBY
+    end
+
+    def test_debugger_removes_rubyopt_added_by_rdbg
+      run_rdbg(program) do
+        type "ENV['RUBYOPT']"
+        assert_no_line_text(/debug\/start/)
+        type "c"
+      end
+    end
+
+    def test_debugger_respects_other_rubyopt
+      run_rdbg(program, rubyopt: "-rreline") do
+        type "ENV['RUBYOPT']"
+        assert_no_line_text(/debug\/start/)
+        assert_line_text(/-rreline/)
+        type "c"
+      end
+    end
+  end
+
   class DebugCommandOptionTest < ConsoleTestCase
     def program
       <<~RUBY

test/support/console_test_case.rb

@@ -246,10 +246,11 @@ def run_ruby program, options: nil, &test_steps
       end
     end
 
-    def run_rdbg program, options: nil, &test_steps
+    def run_rdbg program, options: nil, rubyopt: nil, &test_steps
       prepare_test_environment(program, test_steps) do
         test_info = TestInfo.new(dup_scenario, 'LOCAL', /\(rdbg\)/)
         cmd = "#{RDBG_EXECUTABLE} #{options} -- #{temp_file_path}"
+        cmd = "RUBYOPT=#{rubyopt} #{cmd}" if rubyopt
         run_test_scenario cmd, test_info
       end
     end