Lazily activate the debugger

lib/debug.rb

@@ -1,9 +1,27 @@
 # frozen_string_literal: true
 
-if ENV['RUBY_DEBUG_LAZY']
-  require_relative 'debug/prelude'
-else
-  require_relative 'debug/session'
-  return unless defined?(DEBUGGER__)
-  DEBUGGER__::start no_sigint_hook: true, nonstop: true
+require_relative 'debug/prelude'
+
+module DEBUGGER__
+  def self.step_in(&block)
+    require "debug/session"
+
+    # If session.rb doesn't early return, we can then call the method it defines.
+    if defined?(Session)
+      start no_sigint_hook: true, nonstop: true
+      step_in(&block)
+    # Otherwise, we call the block without stepping in.
+    else
+      yield
+    end
+  end
+
+  def self.start(**kw)
+    require "debug/session"
+
+    # If session.rb doesn't early return, we can then call the method it defines.
+    if defined?(Session)
+      start(**kw)
+    end
+  end
 end

test/console/debugger_method_test.rb

@@ -200,15 +200,6 @@ def test_prelude_defines_debugger_statements
       end
     end
 
-    def test_prelude_doesnt_override_debugger
-      run_ruby(program, options: "-Ilib -rdebug") do
-        assert_line_num(5)
-        type "debugger_source"
-        assert_line_text(/debug\/session\.rb/)
-        type "c"
-      end
-    end
-
     def test_require_config_doesnt_cancel_prelude
       run_ruby(program, options: "-Ilib -rdebug/config") do
         assert_line_num(5)