1 files changed, 55 insertions, 0 deletions
diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 3411c3d701..2d7bdb47fc 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -2890,6 +2890,61 @@ class TestModule < Test::Unit::TestCase
     }
   end
 
+  def test_prepend_constant_lookup
+    m = Module.new do
+      const_set(:C, :m)
+    end
+    c = Class.new do
+      const_set(:C, :c)
+      prepend m
+    end
+    sc = Class.new(c)
+    # Situation from [Bug #17887]
+    assert_equal(sc.ancestors.take(3), [sc, m, c])
+    assert_equal(:m, sc.const_get(:C))
+    assert_equal(:m, sc::C)
+
+    assert_equal(:c, c::C)
+
+    m.send(:remove_const, :C)
+    assert_equal(:c, sc.const_get(:C))
+    assert_equal(:c, sc::C)
+
+    # Same ancestors, built with include instead of prepend
+    m = Module.new do
+      const_set(:C, :m)
+    end
+    c = Class.new do
+      const_set(:C, :c)
+    end
+    sc = Class.new(c) do
+      include m
+    end
+
+    assert_equal(sc.ancestors.take(3), [sc, m, c])
+    assert_equal(:m, sc.const_get(:C))
+    assert_equal(:m, sc::C)
+
+    m.send(:remove_const, :C)
+    assert_equal(:c, sc.const_get(:C))
+    assert_equal(:c, sc::C)
+
+    # Situation from [Bug #17887], but with modules
+    m = Module.new do
+      const_set(:C, :m)
+    end
+    m2 = Module.new do
+      const_set(:C, :m2)
+      prepend m
+    end
+    c = Class.new do
+      include m2
+    end
+    assert_equal(c.ancestors.take(3), [c, m, m2])
+    assert_equal(:m, c.const_get(:C))
+    assert_equal(:m, c::C)
+  end
+
   def test_inspect_segfault
     bug_10282 = '[ruby-core:65214] [Bug #10282]'
     assert_separately [], "#{<<~"begin;"}\n#{<<~'end;'}"