merge revision(s) 548086b34e3dd125edabf5dc1e46b891fad3ea9c,3dc8cde70078ccb38f5f4b0818ad5eecded01bd5,e0cf80d666d4b5df3229f030a16d10d21323508e: [Backport #19529]

	ObjectSpace::WeakMap: fix compaction support

	[Bug #19529]

	`rb_gc_update_tbl_refs` can't be used on `w->obj2wmap` because it's
	not a `VALUE -> VALUE` table, but a `VALUE -> VALUE *` table, so
	we need some dedicated iterator.
	---
	 test/ruby/test_weakmap.rb |  8 ++++++++
	 weakmap.c                 | 37 ++++++++++++++++++++++++++++++++++++-
	 2 files changed, 44 insertions(+), 1 deletion(-)

	Fix crash during compaction

	[Bug #19529]

	The fix for [Bug #19529] in commit 548086b contained a bug that crashes
	on the following script:

	```
	wm = ObjectSpace::WeakMap.new
	obj = Object.new
	100.times do
	  wm[Object.new] = obj
	  GC.start
	end
	GC.compact
	```
	---
	 test/ruby/test_weakmap.rb | 10 ++++++++++
	 weakmap.c                 |  2 +-
	 2 files changed, 11 insertions(+), 1 deletion(-)

	Fix incorrect size of WeakMap buffer

	In wmap_final_func, j is the number of elements + 1 (since j also
	includes the length at the 0th index), so we should resize the buffer
	to size j and the new length is j - 1.
	---
	 weakmap.c | 4 ++--
	 1 file changed, 2 insertions(+), 2 deletions(-)

1 files changed, 18 insertions, 0 deletions

diff --git a/test/ruby/test_weakmap.rb b/test/ruby/test_weakmap.rb
index 86550cc221..9bbe2d6b81 100644
--- a/test/ruby/test_weakmap.rb
+++ b/test/ruby/test_weakmap.rb
@@ -176,4 +176,22 @@ class TestWeakMap < Test::Unit::TestCase
       end
     end;
   end
+
+  def test_compaction_bug_19529
+    obj = Object.new
+    100.times do |i|
+      GC.compact
+      @wm[i] = obj
+    end
+
+    assert_separately(%w(--disable-gems), <<-'end;')
+      wm = ObjectSpace::WeakMap.new
+      obj = Object.new
+      100.times do
+        wm[Object.new] = obj
+        GC.start
+      end
+      GC.compact
+    end;
+  end
 end