From b0190f766370c354e1f9deb69c6b70cc26094ee0 Mon Sep 17 00:00:00 2001
From: Alexander Bulancov <6594487+trinistr@users.noreply.github.com>
Date: Tue, 11 Nov 2025 23:54:04 +0300
Subject: [PATCH 1/2] Add tests for changes to String#+@ in 3.4

---
 core/string/uplus_spec.rb | 44 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 5 deletions(-)

diff --git a/core/string/uplus_spec.rb b/core/string/uplus_spec.rb
index c0b0c49ede..20767bcc01 100644
--- a/core/string/uplus_spec.rb
+++ b/core/string/uplus_spec.rb
@@ -13,14 +13,48 @@
     output.should == 'foobar'
   end
 
-  it 'returns self if the String is not frozen' do
-    input  = 'foo'
+  it 'returns a mutable String itself' do
+    input = String.new("foo")
     output = +input
 
-    output.equal?(input).should == true
+    output.should.equal?(input)
+
+    input << "bar"
+    output.should == "foobar"
+  end
+
+  context 'if file has "frozen_string_literal: true" magic comment' do
+    it 'returns mutable copy of a literal' do
+      ruby_exe(fixture(__FILE__, "freeze_magic_comment.rb")).should == 'mutable'
+    end
   end
 
-  it 'returns mutable copy despite freeze-magic-comment in file' do
-    ruby_exe(fixture(__FILE__, "freeze_magic_comment.rb")).should == 'mutable'
+  context 'if file has "frozen_string_literal: false" magic comment' do
+    it 'returns literal string itself' do
+      input  = 'foo'
+      output = +input
+
+      output.equal?(input).should == true
+    end
+  end
+
+  context 'if file has no frozen_string_literal magic comment' do
+    ruby_version_is ''...'3.4' do
+      it 'returns literal string itself' do
+        eval(<<~RUBY).should == true
+          s = "foo"
+          s.equal?(+s)
+        RUBY
+      end
+    end
+
+    ruby_version_is '3.4' do
+      it 'returns mutable copy of a literal' do
+        eval(<<~RUBY).should == false
+          s = "foo"
+          s.equal?(+s)
+        RUBY
+      end
+    end
   end
 end

From 80c71353c968b02879db00bb3636a157e1679873 Mon Sep 17 00:00:00 2001
From: Alexander Bulancov <6594487+trinistr@users.noreply.github.com>
Date: Wed, 12 Nov 2025 00:23:39 +0300
Subject: [PATCH 2/2] Add test for warning about modifying chilled literal
 strings

---
 command_line/frozen_strings_spec.rb | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/command_line/frozen_strings_spec.rb b/command_line/frozen_strings_spec.rb
index 014153e0b4..8acab5bc1d 100644
--- a/command_line/frozen_strings_spec.rb
+++ b/command_line/frozen_strings_spec.rb
@@ -42,8 +42,28 @@
     ruby_exe(fixture(__FILE__, "freeze_flag_one_literal.rb")).chomp.should == "false"
   end
 
-  it "if file has no frozen_string_literal comment produce different mutable strings each time" do
-    ruby_exe(fixture(__FILE__, "string_literal_raw.rb")).chomp.should == "frozen:false interned:false"
+  context "if file has no frozen_string_literal comment" do
+    it "produce different mutable strings each time" do
+      ruby_exe(fixture(__FILE__, "string_literal_raw.rb")).chomp.should == "frozen:false interned:false"
+    end
+
+    guard -> { ruby_version_is "3.4" and !"test".frozen? } do
+      it "complain about modification of produced mutable strings" do
+        -> { eval(<<~RUBY) }.should complain(/warning: literal string will be frozen in the future \(run with --debug-frozen-string-literal for more information\)/)
+          "test" << "!"
+        RUBY
+      end
+
+      it "does not complain about modification if Warning[:deprecated] is false" do
+        deprecated = Warning[:deprecated]
+        Warning[:deprecated] = false
+        -> { eval(<<~RUBY) }.should_not complain
+          "test" << "!"
+        RUBY
+      ensure
+        Warning[:deprecated] = deprecated
+      end
+    end
   end
 
   it "if file has frozen_string_literal:true comment produce same frozen strings each time" do