merge revision(s) ec8e5f5aa64e2a54cf1e303f2b012c98e8d521ba,5a187e26adc8aa32367f294c1496935c7356d386: [Backport #15952]

array.c: always check frozenness in Array#unshift. Fixes [Bug #15952]

	Closes: https://github.com/ruby/ruby/pull/2251

	array.c add back shared array optimization to
	 ary_ensure_room_for_unshift

	Bug fix in commit ec8e5f5aa6 [Bug #15952] disabled an
	optimization in this function.

	Closes: https://github.com/ruby/ruby/pull/2252

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67740 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

array.c

@@ -1368,6 +1368,7 @@ ary_ensure_room_for_unshift(VALUE ary, int argc)
 	VALUE shared = ARY_SHARED(ary);
 	capa = RARRAY_LEN(shared);
 	if (ARY_SHARED_OCCUPIED(shared) && capa > new_len) {
+            rb_ary_modify_check(ary);
             head = RARRAY_CONST_PTR_TRANSIENT(ary);
             sharedp = RARRAY_CONST_PTR_TRANSIENT(shared);
 	    goto makeroom_if_need;

test/ruby/test_array.rb

@@ -1934,6 +1934,17 @@ class TestArray < Test::Unit::TestCase
     assert_equal(@cls[@cls[1,2], nil, 'dog', 'cat'], a.unshift(@cls[1, 2]))
   end
 
+  def test_unshift_frozen
+    bug15952 = '[Bug #15952]'
+    assert_raise(FrozenError, bug15952) do
+      a = [1] * 100
+      b = a[4..-1]
+      a.replace([1])
+      b.freeze
+      b.unshift("a")
+    end
+  end
+
   def test_OR # '|'
     assert_equal(@cls[],  @cls[]  | @cls[])
     assert_equal(@cls[1], @cls[1] | @cls[])

version.h

@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.6.3"
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 90
+#define RUBY_PATCHLEVEL 91
 
 #define RUBY_RELEASE_YEAR 2019
 #define RUBY_RELEASE_MONTH 8