From 10ea05d3aa8e0f731aac168ccb4dcadb07a5d7ce Mon Sep 17 00:00:00 2001
From: "Yukihiro \"Matz\" Matsumoto" <matz@ruby.or.jp>
Date: Fri, 20 Jun 2025 13:34:32 +0900
Subject: [PATCH] mruby-set: refactor Set#union (+, |)

The code is written by Atlassian Rovodev.
---
 mrbgems/mruby-set/mrblib/set.rb | 19 +++++++++++++
 mrbgems/mruby-set/src/set.c     | 48 ++++++++++++++++++++++-----------
 2 files changed, 51 insertions(+), 16 deletions(-)

diff --git a/mrbgems/mruby-set/mrblib/set.rb b/mrbgems/mruby-set/mrblib/set.rb
index 4f196c852..9a34eb387 100644
--- a/mrbgems/mruby-set/mrblib/set.rb
+++ b/mrbgems/mruby-set/mrblib/set.rb
@@ -46,6 +46,25 @@ class Set
   # Alias for #intersection
   alias & intersection
 
+  # Returns a new set built by merging the set and the elements of the given
+  # enumerable object.
+  #
+  # @param [Enumerable] enum The enumerable object to merge with
+  # @return [Set] A new set containing all elements from both
+  def union(enum)
+    if enum.is_a?(Set)
+      # Fast path: Call C-implemented function for Set-to-Set union
+      __set_union(enum)
+    else
+      # General path: Create a duplicate and merge the enumerable
+      dup.merge(enum)
+    end
+  end
+
+  # Aliases for #union
+  alias | union
+  alias + union
+
   # Returns a new set containing elements exclusive between the set and the given
   # enumerable object.
   #
diff --git a/mrbgems/mruby-set/src/set.c b/mrbgems/mruby-set/src/set.c
index 8d2dfa9ee..e28b426b8 100644
--- a/mrbgems/mruby-set/src/set.c
+++ b/mrbgems/mruby-set/src/set.c
@@ -410,23 +410,41 @@ set_subtract(mrb_state *mrb, mrb_value self)
 }
 
 /*
- * call-seq:
- *   set | enum -> new_set
- *   set + enum -> new_set
- *   set.union(enum) -> new_set
- *
- * Returns a new set built by merging the set and the elements of the given
- * enumerable object.
+ * Core implementation of Set-to-Set union
+ * This is an internal method that will be called from Ruby
  */
 static mrb_value
-set_union(mrb_state *mrb, mrb_value self)
+set_core_union(mrb_state *mrb, mrb_value self)
 {
-  mrb_value enum_obj;
-  mrb_value new_set;
+  mrb_value other;
+  mrb_value result_set;
+  khash_t(set) *result_kh, *self_kh, *other_kh;
 
-  mrb_get_args(mrb, "o", &enum_obj);
-  new_set = mrb_funcall_id(mrb, self, MRB_SYM(dup), 0);
-  return mrb_funcall_id(mrb, new_set, MRB_SYM(merge), 1, enum_obj);
+  mrb_get_args(mrb, "o", &other);
+
+  /* Create a new set by duplicating self */
+  result_set = mrb_obj_dup(mrb, self);
+  result_kh = set_get_khash(mrb, result_set);
+  if (!result_kh) {
+    /* If self is empty, create a new empty set */
+    result_kh = kh_init(set, mrb);
+    set_set_khash(mrb, result_set, result_kh);
+  }
+
+  /* Add all elements from other set */
+  other_kh = set_get_khash(mrb, other);
+  if (other_kh) {
+    khiter_t k;
+    int ai = mrb_gc_arena_save(mrb);
+    for (k = kh_begin(other_kh); k != kh_end(other_kh); k++) {
+      if (kh_exist(other_kh, k)) {
+        kh_put(set, mrb, result_kh, kh_key(other_kh, k));
+        mrb_gc_arena_restore(mrb, ai);
+      }
+    }
+  }
+
+  return result_set;
 }
 
 /*
@@ -925,9 +943,7 @@ mrb_mruby_set_gem_init(mrb_state *mrb)
   mrb_define_method(mrb, set, "merge", set_merge, MRB_ARGS_REQ(1));
   mrb_define_method(mrb, set, "subtract", set_subtract, MRB_ARGS_REQ(1));
 
-  mrb_define_method(mrb, set, "|", set_union, MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, set, "+", set_union, MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, set, "union", set_union, MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, set, "__set_union", set_core_union, MRB_ARGS_REQ(1));
 
   mrb_define_method(mrb, set, "-", set_difference, MRB_ARGS_REQ(1));
   mrb_define_method(mrb, set, "difference", set_difference, MRB_ARGS_REQ(1));