merge revision(s) 31e0382723bfb35cffe3ca485dd0577668cafa07,5e5fb72f99701dc27c66ab148471893f14e6d6f0,fb6ebe55d91187d9635e0183d47dbf38e95b1141,522d4cd32f7727886f4fcbc28ed29c08d361ee20: [Backport #17735]

	Keep non evaluated keys in `Hash#transform_keys!` [Bug #17735]

	---
	 hash.c                                     |  6 +++++-
	 spec/ruby/core/hash/transform_keys_spec.rb | 12 +++++++++++-
	 test/ruby/test_hash.rb                     |  8 ++++++++
	 3 files changed, 24 insertions(+), 2 deletions(-)

	Clear an intermediate hash [Bug #17735]

	---
	 hash.c | 1 +
	 1 file changed, 1 insertion(+)

	Hide an intermediate array

	---
	 hash.c | 6 ++++--
	 1 file changed, 4 insertions(+), 2 deletions(-)

	Force recycle intermediate collection in Hash#transform_keys! [Bug
	 #17735]

	* Force recycle intermediate hash

	* Force recycle intermediate array too

	https://github.com/ruby/ruby/pull/4329#issuecomment-808840718
	---
	 hash.c | 2 ++
	 1 file changed, 2 insertions(+)

1 files changed, 12 insertions, 3 deletions

diff --git a/hash.c b/hash.c
index 0ed2692f24..e29e98598a 100644
--- a/hash.c
+++ b/hash.c
@@ -3249,7 +3249,7 @@ rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
     return result;
 }
 
-static VALUE rb_hash_flatten(int argc, VALUE *argv, VALUE hash);
+static int flatten_i(VALUE key, VALUE val, VALUE ary);
 
 /*
  *  call-seq:
@@ -3278,8 +3278,9 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
     rb_hash_modify_check(hash);
     if (!RHASH_TABLE_EMPTY_P(hash)) {
         long i;
-        VALUE pairs = rb_hash_flatten(0, NULL, hash);
-        rb_hash_clear(hash);
+        VALUE new_keys = hash_alloc(0);
+        VALUE pairs = rb_ary_tmp_new(RHASH_SIZE(hash) * 2);
+        rb_hash_foreach(hash, flatten_i, pairs);
         for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
             VALUE key = RARRAY_AREF(pairs, i), new_key, val;
 
@@ -3296,8 +3297,16 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
                 new_key = key;
             }
             val = RARRAY_AREF(pairs, i+1);
+            if (!hash_stlike_lookup(new_keys, key, NULL)) {
+                rb_hash_stlike_delete(hash, &key, NULL);
+            }
             rb_hash_aset(hash, new_key, val);
+            rb_hash_aset(new_keys, new_key, Qnil);
         }
+        rb_ary_clear(pairs);
+        rb_gc_force_recycle(pairs);
+        rb_hash_clear(new_keys);
+        rb_gc_force_recycle(new_keys);
     }
     return hash;
 }