don't prepend InstructionSequence#load_iseq if ruby version is < 2.5

ext/debase_internals.c

@@ -637,7 +637,7 @@ Debase_enable_file_filtering(VALUE self, VALUE value)
   return value;
 }
 
-#if RUBY_API_VERSION_CODE >= 20500
+#if RUBY_API_VERSION_CODE >= 20500 && !(RUBY_RELEASE_YEAR == 2017 && RUBY_RELEASE_MONTH == 10 && RUBY_RELEASE_DAY == 10)
     static const rb_iseq_t *
     my_iseqw_check(VALUE iseqw)
     {
@@ -654,17 +654,28 @@ Debase_enable_file_filtering(VALUE self, VALUE value)
     }
 
     static void
-    Debase_set_trace_flag_to_iseq(VALUE self, VALUE rb_iseq)
-    {
+    Debase_set_trace_flag_to_iseq(VALUE self, VALUE rb_iseq) {
         if (!SPECIAL_CONST_P(rb_iseq) && RBASIC_CLASS(rb_iseq) == rb_cISeq) {
             rb_iseq_t *iseq = my_iseqw_check(rb_iseq);
             rb_iseq_trace_set(iseq, RUBY_EVENT_TRACEPOINT_ALL);
         }
     }
+
+    static void
+    Debase_unset_trace_flags(VALUE self, VALUE rb_iseq) {
+        if (!SPECIAL_CONST_P(rb_iseq) && RBASIC_CLASS(rb_iseq) == rb_cISeq) {
+            rb_iseq_t *iseq = my_iseqw_check(rb_iseq);
+            rb_iseq_trace_set(iseq, RUBY_EVENT_NONE);
+        }
+    }
 #else
       static void
       Debase_set_trace_flag_to_iseq(VALUE self, VALUE rb_iseq) {
       }
+
+      static void
+      Debase_unset_trace_flags(VALUE self, VALUE rb_iseq) {
+      }
 #endif
 
 static VALUE
@@ -712,6 +723,9 @@ Init_debase_internals()
   rb_define_module_function(mDebase, "init_variables", Debase_init_variables, 0);
   rb_define_module_function(mDebase, "set_trace_flag_to_iseq", Debase_set_trace_flag_to_iseq, 1);
 
+  //use only for tests
+  rb_define_module_function(mDebase, "unset_iseq_flags", Debase_unset_trace_flags, 1);
+
   idAlive = rb_intern("alive?");
   idAtLine = rb_intern("at_line");
   idAtBreakpoint = rb_intern("at_breakpoint");

lib/debase.rb

@@ -30,7 +30,7 @@ def monkey_patch_prepend
       class << RubyVM::InstructionSequence
         def self.prepend(mod, *smth)
           super
-          if mod.to_s.include? 'Bootsnap'
+          if mod.to_s.include?('Bootsnap') && RUBY_VERSION >= "2.5"
             prepend InstructionSequenceMixin
           end
         end
@@ -107,7 +107,7 @@ def load_iseq(path)
 
       def do_set_flags(iseq)
         Debugger.set_trace_flag_to_iseq(iseq)
-        iseq.each_child{|child_iseq| do_set_flags(child_iseq)}
+        iseq.each_child { |child_iseq| do_set_flags(child_iseq) } if iseq.respond_to? :each_child
       end
     end
   end

test/example/bootsnap/a.rb

@@ -0,0 +1,5 @@
+class A
+  def foo(a)
+    puts a
+  end
+end

test/example/bootsnap/bootsnap.rb

@@ -0,0 +1,3 @@
+require_relative 'a.rb'
+
+A.new.foo('hi')

test/test_load.rb

@@ -3,6 +3,9 @@
 
 # Test of Debugger.debug_load in C extension ruby_debug.so
 class TestDebugLoad < Test::Unit::TestCase
+
+  self.test_order = :defined
+
   class << self
     def at_line(file, line)
       @@at_line = [File.basename(file), line]
@@ -41,4 +44,35 @@ def test_debug_load
   ensure
     Debugger.stop if Debugger.started?
   end
+
+  module MyBootsnap
+    def load_iseq(path)
+      iseq = RubyVM::InstructionSequence.compile_file(path)
+
+      Debugger.unset_iseq_flags(iseq)
+      iseq
+    end
+  end
+
+  def test_bootsnap
+    @@at_line = nil
+    src_dir = File.dirname(__FILE__)
+    prog_script = File.join(src_dir, 'example', 'bootsnap', 'bootsnap.rb')
+
+    class << RubyVM::InstructionSequence
+      prepend MyBootsnap
+    end
+    bt = Debugger.debug_load(prog_script, true)
+    assert_equal(nil, bt)
+    assert_not_nil(@@at_line)
+    if RUBY_VERSION >= '2.5'
+      assert_equal(['debase.rb', 101], @@at_line)
+    end
+
+    assert(Debugger.started?)
+    Debugger.stop
+
+    class << RubyVM::InstructionSequence; self end.class_eval { undef_method :load_iseq }
+
+  end
 end