Do not allow Module#include to insert modules before the origin in the lookup chain

Module#include should only be able to insert modules after the origin,
otherwise it ends up working like Module#prepend.

This fixes the case where one of the modules in the included module
chain is included in a module that is already prepended to the receiver.

Fixes [Bug #7844]

Backport of https://github.com/ruby/ruby/pull/3796 to 2.7

1 files changed, 10 insertions, 0 deletions

diff --git a/test/ruby/test_module.rb b/test/ruby/test_module.rb
index 5cfda018f3..231ccd2072 100644
--- a/test/ruby/test_module.rb
+++ b/test/ruby/test_module.rb
@@ -472,6 +472,16 @@ class TestModule < Test::Unit::TestCase
     assert_equal([Comparable, Kernel], String.included_modules - mixins)
   end
 
+  def test_include_with_prepend
+    c = Class.new{def m; [:c] end}
+    p = Module.new{def m; [:p] + super end}
+    q = Module.new{def m; [:q] + super end; include p}
+    r = Module.new{def m; [:r] + super end; prepend q}
+    s = Module.new{def m; [:s] + super end; include r}
+    a = Class.new(c){def m; [:a] + super end; prepend p; include s}
+    assert_equal([:p, :a, :s, :q, :r, :c], a.new.m)
+  end
+
   def test_instance_methods
     assert_equal([:user, :user2], User.instance_methods(false).sort)
     assert_equal([:user, :user2, :mixin].sort, User.instance_methods(true).sort)