merge revision(s) 496591de96b261b8789332c7f8b2bfbd17658955: [Backport #18578]

    st.c: Do not clear entries_bound when calling Hash#shift for empty
     hash

    tab->entries_bound is used to check if the bins are full in
    rebuild_table_if_necessary.

    Hash#shift against an empty hash assigned 0 to tab->entries_bound, but
    didn't clear the bins. Thus, the table is not rebuilt even when the bins
    are full. Attempting to add a new element into full-bin hash gets stuck.

    This change stops clearing tab->entries_bound in Hash#shift.
    [Bug #18578]
    ---
     st.c                   |  1 -
     test/ruby/test_hash.rb | 13 +++++++++++++
     2 files changed, 13 insertions(+), 1 deletion(-)

3 files changed, 14 insertions, 2 deletions

diff --git a/st.c b/st.c
index 4258f93ffc..599f93a463 100644
--- a/st.c
+++ b/st.c
@@ -1486,7 +1486,6 @@ st_shift(st_table *tab, st_data_t *key, st_data_t *value)
 	}
     }
     st_assert(tab->num_entries == 0);
-    tab->entries_start = tab->entries_bound = 0;
     if (value != 0) *value = 0;
     return 0;
 }
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 046ea40f5d..d4af130a07 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -983,6 +983,19 @@ class TestHash < Test::Unit::TestCase
     assert_equal("FOO", h.shift)
   end
 
+  def test_shift_for_empty_hash
+    # [ruby-dev:51159]
+    h = @cls[]
+    100.times{|n|
+      while h.size < n
+        k = Random.rand 0..1<<30
+        h[k] = 1
+      end
+      0 while h.shift
+      assert_equal({}, h)
+    }
+  end
+
   def test_reject_bang2
     assert_equal({1=>2}, @cls[1=>2,3=>4].reject! {|k, v| k + v == 7 })
     assert_nil(@cls[1=>2,3=>4].reject! {|k, v| k == 5 })
diff --git a/version.h b/version.h
index 944a877c76..23d557496e 100644
--- a/version.h
+++ b/version.h
@@ -2,7 +2,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 6
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 217
+#define RUBY_PATCHLEVEL 218
 
 #define RUBY_RELEASE_YEAR 2022
 #define RUBY_RELEASE_MONTH 3