Make it possible to dump and load an exception object

A backtrace object in an exception had never supported marshalling
correctly: `Marshal.load(Marshal.dump(exc)).backtrace_locations` dumped
core.

An Exception object has two hidden instance varibles for backtrace data:
one is "bt", which has an Array of Strings, and the other is
"bt_locations", which has an Array of Thread::Backtrace::Locations.
However, Exception's dump outputs data so that the two variables are the
same Array of Strings. Thus, "bt_locations" had a wrong-type object.

For the compatibility, it is difficult to change the dump format.  This
changeset fixes the issue by ignoring data for "bt_locations" at the
loading phase if "bt_locations" refers to the same object as "bt".

Future work: Exception's dump should output "bt_locations"
appropriately.

https://bugs.ruby-lang.org/issues/17150

1 files changed, 31 insertions, 0 deletions

diff --git a/test/ruby/test_marshal.rb b/test/ruby/test_marshal.rb
index 1d096adb18..fd62ea774b 100644
--- a/test/ruby/test_marshal.rb
+++ b/test/ruby/test_marshal.rb
@@ -780,4 +780,35 @@ class TestMarshal < Test::Unit::TestCase
     hash = Marshal.load(Marshal.dump(flagged_hash))
     assert_equal(42, ruby2_keywords_test(*[hash]))
   end
+
+  def exception_test
+    raise
+  end
+
+  def test_marshal_exception
+    begin
+      exception_test
+    rescue => e
+      e2 = Marshal.load(Marshal.dump(e))
+      assert_equal(e.message, e2.message)
+      assert_equal(e.backtrace, e2.backtrace)
+      assert_nil(e2.backtrace_locations) # temporal
+    end
+  end
+
+  def nameerror_test
+    unknown_method
+  end
+
+  def test_marshal_nameerror
+    begin
+      nameerror_test
+    rescue NameError => e
+      e2 = Marshal.load(Marshal.dump(e))
+      assert_equal(e.message, e2.message)
+      assert_equal(e.name, e2.name)
+      assert_equal(e.backtrace, e2.backtrace)
+      assert_nil(e2.backtrace_locations) # temporal
+    end
+  end
 end