From a61f033ded2bb2a3d77d520173a323d6401a191e Mon Sep 17 00:00:00 2001
From: Josh Wilson <joshuaw@squareup.com>
Date: Fri, 3 Jul 2026 17:03:48 -0500
Subject: [PATCH] Fix serializer crash when multi_json is loaded without
 RubyGems activation

Since 8.5.2, `Serializer::MultiJson#deprecated_gem_version_loaded?`
decides between the deprecated `MultiJson` API and the new `MultiJSON`
API by consulting `Gem.loaded_specs['multi_json'].version`. When the gem
is loaded from a plain $LOAD_PATH without RubyGems activation -- e.g.
from a `bundle install --standalone` bundle or a vendored load path --
`Gem.loaded_specs` is empty, so every request fails with:

    NoMethodError: undefined method 'version' for nil

Detect the API by checking for the `MultiJSON` constant instead:
multi_json 1.21.0 is exactly the version that introduced that constant,
so the check is equivalent, and it works regardless of how the gem was
loaded.
---
 .../transport/serializer/multi_json.rb          |  8 +++++++-
 test/unit/serializer_test.rb                    | 17 +++++++++++++----
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/lib/elastic/transport/transport/serializer/multi_json.rb b/lib/elastic/transport/transport/serializer/multi_json.rb
index 1da59314..551ac545 100644
--- a/lib/elastic/transport/transport/serializer/multi_json.rb
+++ b/lib/elastic/transport/transport/serializer/multi_json.rb
@@ -56,8 +56,14 @@ def dump(object, options = {})
 
           private
 
+          # multi_json 1.21.0 renamed the top-level constant to `MultiJSON` (keeping a
+          # deprecated `MultiJson` alias), so the constant's absence indicates a deprecated
+          # version. Checking the constant rather than `Gem.loaded_specs` also works when
+          # the gem is loaded without RubyGems activation (e.g. from a `bundle install
+          # --standalone` bundle or a vendored load path), where `Gem.loaded_specs` is
+          # empty and the version lookup would raise a `NoMethodError` on `nil`.
           def deprecated_gem_version_loaded?
-            Gem.loaded_specs['multi_json'].version < Gem::Version.create('1.21.0')
+            !defined?(::MultiJSON)
           end
         end
       end
diff --git a/test/unit/serializer_test.rb b/test/unit/serializer_test.rb
index c65c3be3..bfb24fa1 100644
--- a/test/unit/serializer_test.rb
+++ b/test/unit/serializer_test.rb
@@ -22,18 +22,27 @@ class Elastic::Transport::Transport::SerializerTest < Minitest::Test
   context "Serializer" do
 
     should "use MultiJSON by default" do
-      if Gem.loaded_specs['multi_json'].version < Gem::Version.create('1.21.0')
-        ::MultiJson.expects(:load)
-        ::MultiJson.expects(:dump)
-      else
+      if defined?(::MultiJSON)
         ::MultiJSON.expects(:parse)
         ::MultiJSON.expects(:generate)
+      else
+        ::MultiJson.expects(:load)
+        ::MultiJson.expects(:dump)
       end
 
       Elastic::Transport::Transport::Serializer::MultiJson.new.load('{}')
       Elastic::Transport::Transport::Serializer::MultiJson.new.dump({})
     end
 
+    should "work when multi_json is loaded without RubyGems activation" do
+      # When gems are loaded from a plain $LOAD_PATH (e.g. a `bundle install --standalone`
+      # bundle or a vendored load path), they are not registered in Gem.loaded_specs.
+      Gem.stubs(:loaded_specs).returns({})
+
+      assert_equal({ 'foo' => 'bar' }, Elastic::Transport::Transport::Serializer::MultiJson.new.load('{"foo":"bar"}'))
+      assert_equal('{"foo":"bar"}', Elastic::Transport::Transport::Serializer::MultiJson.new.dump({ 'foo' => 'bar' }))
+    end
+
   end
 
 end