From 5d1f9febcc61be349a7b23e64c040331f4023d99 Mon Sep 17 00:00:00 2001
From: Hartley McGuire <skipkayhil@gmail.com>
Date: Fri, 31 Jul 2026 15:11:16 -0400
Subject: [PATCH 1/2] Fix Ractor compatibility regression, add tests

The recent change to use `BasicObject.instance_method(:equal?)` broke
the ability to share frozen ERB templates across Ractors because
`UnboundMethod` isn't shareable.

Freezing the `UnboundMethod` _may_ fix the issue (dependong on Ruby
version), but replacing the constant with an inline call to the
`singleton_class` is simpler (and still avoids calling `equal?` on
`@init`).

There have previously been many contributions to make ERB Ractor safe,
but no tests added to ensure it continues to be Ractor safe, so this
commit also adds some regression tests.
---
 lib/erb.rb           |  5 +----
 test/erb/test_erb.rb | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/lib/erb.rb b/lib/erb.rb
index 0c4653d..040cd18 100644
--- a/lib/erb.rb
+++ b/lib/erb.rb
@@ -815,9 +815,6 @@
 # [template processor]: https://en.wikipedia.org/wiki/Template_processor
 #
 class ERB
-  IDENTITY_METHOD = BasicObject.instance_method(:equal?) # :nodoc:
-  private_constant :IDENTITY_METHOD
-
   # :markup: markdown
   #
   # :call-seq:
@@ -1117,7 +1114,7 @@ def new_toplevel(vars = nil)
   private :new_toplevel
 
   def initialized_by_new? # :nodoc:
-    IDENTITY_METHOD.bind_call(@_init, self.class.singleton_class)
+    self.class.singleton_class.equal? @_init
   end
   private :initialized_by_new?
 
diff --git a/test/erb/test_erb.rb b/test/erb/test_erb.rb
index 1de8925..6da2514 100644
--- a/test/erb/test_erb.rb
+++ b/test/erb/test_erb.rb
@@ -740,3 +740,43 @@ def teardown
     ERB::Compiler::Scanner.instance_variable_set('@scanner_map', @save_map)
   end
 end
+
+class TestERBRactor < Test::Unit::TestCase
+  def test_compile_and_result_in_ractor
+    assert_ractor(<<~RUBY, require: 'erb')
+      r = Ractor.new do
+        ERB.new("Hello, <%= 'world' %>!").result(binding)
+      end
+      assert_equal("Hello, world!", r.value)
+    RUBY
+  end
+
+  def test_trim_mode_in_ractor
+    assert_ractor(<<~RUBY, require: 'erb')
+      src = "<% [1, 2].each do |i| %>\\n<%= i %>\\n<% end %>\\n"
+      r = Ractor.new(src) { |s| ERB.new(s, trim_mode: '-').result(binding) }
+      assert_equal("\\n1\\n\\n2\\n\\n", r.value)
+
+      r = Ractor.new(src) { |s| ERB.new(s, trim_mode: '<>').result(binding) }
+      assert_equal("12", r.value)
+    RUBY
+  end
+
+  def test_frozen_erb_instance_reused_across_ractors
+    assert_ractor(<<~RUBY, require: 'erb')
+      erb = ERB.new("<%= 1 + 1 %>")
+      erb.freeze
+      rs = 2.times.map { Ractor.new(erb) { |e| e.result(binding) } }
+      assert_equal(["2", "2"], rs.map(&:value))
+    RUBY
+  end
+
+  def test_util_html_escape_in_ractor
+    assert_ractor(<<~RUBY, require: 'erb')
+      r = Ractor.new do
+        ERB::Util.html_escape("<script>")
+      end
+      assert_equal("&lt;script&gt;", r.value)
+    RUBY
+  end
+end

From c8373d7af35080c75e341463efa19bbc6089ab95 Mon Sep 17 00:00:00 2001
From: Hartley McGuire <skipkayhil@gmail.com>
Date: Fri, 31 Jul 2026 15:11:23 -0400
Subject: [PATCH 2/2] Simplify Scanner's Ractor safety code

Ractor.make_shareable isn't needed if everything is plain `freeze`d
---
 lib/erb/compiler.rb | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/lib/erb/compiler.rb b/lib/erb/compiler.rb
index 6d70288..b6185cd 100644
--- a/lib/erb/compiler.rb
+++ b/lib/erb/compiler.rb
@@ -80,16 +80,11 @@ def initialize(str)
   end
 
   class Scanner # :nodoc:
-    @scanner_map = defined?(Ractor) ? Ractor.make_shareable({}) : {}
+    @scanner_map = {}.freeze
+
     class << self
-      if defined?(Ractor)
-        def register_scanner(klass, trim_mode, percent)
-          @scanner_map = Ractor.make_shareable({ **@scanner_map, [trim_mode, percent] => klass })
-        end
-      else
-        def register_scanner(klass, trim_mode, percent)
-          @scanner_map[[trim_mode, percent]] = klass
-        end
+      def register_scanner(klass, trim_mode, percent)
+        @scanner_map = @scanner_map.merge([trim_mode, percent].freeze => klass).freeze
       end
       alias :regist_scanner :register_scanner
     end