Fix stack trace for rescued StopIteration

enumerator.c

@@ -165,7 +165,10 @@ static VALUE sym_each, sym_cycle, sym_yield;
 
 static VALUE lazy_use_super_method;
 
+extern ID ruby_static_id_cause;
+
 #define id_call idCall
+#define id_cause ruby_static_id_cause
 #define id_each idEach
 #define id_eqq idEqq
 #define id_initialize idInitialize
@@ -787,8 +790,16 @@ get_next_values(VALUE obj, struct enumerator *e)
 {
     VALUE curr, vs;
 
-    if (e->stop_exc)
-        rb_exc_raise(e->stop_exc);
+    if (e->stop_exc) {
+        VALUE exc = e->stop_exc;
+        VALUE result = rb_attr_get(exc, id_result);
+        VALUE mesg = rb_attr_get(exc, idMesg);
+        if (!NIL_P(mesg)) mesg = rb_str_dup(mesg);
+        VALUE stop_exc = rb_exc_new_str(rb_eStopIteration, mesg);
+        rb_ivar_set(stop_exc, id_cause, exc);
+        rb_ivar_set(stop_exc, id_result, result);
+        rb_exc_raise(stop_exc);
+    }
 
     curr = rb_fiber_current();
 

test/ruby/test_enumerator.rb

@@ -244,6 +244,26 @@ class TestEnumerator < Test::Unit::TestCase
     assert_equal(res, exc.result)
   end
 
+  def test_stopiteration_rescue
+    e = [1].each
+    res = e.each {}
+    e.next
+    exc0 = assert_raise(StopIteration) { e.peek }
+    assert_include(exc0.backtrace.first, "test_enumerator.rb:#{__LINE__-1}:")
+    assert_nil(exc0.cause)
+    assert_equal(res, exc0.result)
+
+    exc1 = assert_raise(StopIteration) { e.next }
+    assert_include(exc1.backtrace.first, "test_enumerator.rb:#{__LINE__-1}:")
+    assert_same(exc0, exc1.cause)
+    assert_equal(res, exc1.result)
+
+    exc2 = assert_raise(StopIteration) { e.next }
+    assert_include(exc2.backtrace.first, "test_enumerator.rb:#{__LINE__-1}:")
+    assert_same(exc0, exc2.cause)
+    assert_equal(res, exc2.result)
+  end
+
   def test_next_values
     o = Object.new
     def o.each