Mark array as "going to be modified" in `Array#reject!`

Before this patch, if `reject!` is called on a shared array it can
mutate the shared array rather than a copy.  This patch marks the array
as "going to be modified" so that the shared source array isn't
mutated.

[Bug #15479] [ruby-core:90781]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66756 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

array.c

@@ -3540,6 +3540,7 @@ static VALUE
 rb_ary_reject_bang(VALUE ary)
 {
     RETURN_SIZED_ENUMERATOR(ary, 0, 0, ary_enum_length);
+    rb_ary_modify(ary);
     return ary_reject_bang(ary);
 }
 

test/ruby/test_array.rb

@@ -1308,6 +1308,65 @@ class TestArray < Test::Unit::TestCase
     assert_equal(@cls[7, 8, 9, 10], a, bug2545)
   end
 
+  def test_shared_array_reject!
+    c = []
+    b = [1, 2, 3, 4]
+    3.times do
+      a = b.dup
+      c << a.dup
+
+      begin
+        a.reject! do |x|
+          case x
+          when 2 then true
+          when 3 then raise StandardError, 'Oops'
+          else false
+          end
+        end
+      rescue StandardError
+      end
+
+      c << a.dup
+    end
+
+    bug90781 = '[ruby-core:90781]'
+    assert_equal [[1, 2, 3, 4],
+                  [1, 3, 4],
+                  [1, 2, 3, 4],
+                  [1, 3, 4],
+                  [1, 2, 3, 4],
+                  [1, 3, 4]], c, bug90781
+  end
+
+  def test_iseq_shared_array_reject!
+    c = []
+    3.times do
+      a = [1, 2, 3, 4]
+      c << a.dup
+
+      begin
+        a.reject! do |x|
+          case x
+          when 2 then true
+          when 3 then raise StandardError, 'Oops'
+          else false
+          end
+        end
+      rescue StandardError
+      end
+
+      c << a.dup
+    end
+
+    bug90781 = '[ruby-core:90781]'
+    assert_equal [[1, 2, 3, 4],
+                  [1, 3, 4],
+                  [1, 2, 3, 4],
+                  [1, 3, 4],
+                  [1, 2, 3, 4],
+                  [1, 3, 4]], c, bug90781
+  end
+
   def test_replace
     a = @cls[ 1, 2, 3]
     a_id = a.__id__