node.c (rb_ast_new): imemo_ast is WB-unprotected

Previously imemo_ast was handled as WB-protected which caused a segfault
of the following code:

    # shareable_constant_value: literal
    M0 = {}
    M1 = {}
    ...
    M100000 = {}

My analysis is here: `shareable_constant_value: literal` creates many
Hash instances during parsing, and add them to node_buffer of imemo_ast.
However, the contents are missed because imemo_ast is incorrectly
WB-protected.

This changeset makes imemo_ast as WB-unprotected.

1 files changed, 7 insertions, 0 deletions

diff --git a/test/ruby/test_gc.rb b/test/ruby/test_gc.rb
index 1f75a34cac..f10946bd39 100644
--- a/test/ruby/test_gc.rb
+++ b/test/ruby/test_gc.rb
@@ -494,4 +494,11 @@ class TestGc < Test::Unit::TestCase
     b = 1000.times.map { Object.new.object_id }
     assert_empty(a & b)
   end
+
+  def test_ast_node_buffer
+    # https://github.com/ruby/ruby/pull/4416
+    Module.new.class_eval do
+      eval((["# shareable_constant_value: literal"] + (0..100000).map {|i| "M#{ i } = {}" }).join("\n"))
+    end
+  end
 end