Fix assignment for frozen value in HWIA

3 files changed, 15 insertions, 1 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index f6c236bc35..2caf0b27ee 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Duplicate frozen array when assigning it to a HashWithIndifferentAccess so
+    that it doesn't raise a `RuntimeError` when calling `map!` on it in `convert_value`.
+
+    Fixes #18550.
+
+    *Aditya Kapoor*
+
 *   Add missing time zone definitions for Russian Federation and sync them
     with `zone.tab` file from tzdata version 2014j (latest).
 
diff --git a/activesupport/lib/active_support/hash_with_indifferent_access.rb b/activesupport/lib/active_support/hash_with_indifferent_access.rb
index 1468c62151..4f71f13971 100644
--- a/activesupport/lib/active_support/hash_with_indifferent_access.rb
+++ b/activesupport/lib/active_support/hash_with_indifferent_access.rb
@@ -267,7 +267,7 @@ module ActiveSupport
             value.nested_under_indifferent_access
           end
         elsif value.is_a?(Array)
-          unless options[:for] == :assignment
+          if options[:for] != :assignment || value.frozen?
             value = value.dup
           end
           value.map! { |e| convert_value(e, options) }
diff --git a/activesupport/test/hash_with_indifferent_access_test.rb b/activesupport/test/hash_with_indifferent_access_test.rb
index 843994147b..880457386e 100644
--- a/activesupport/test/hash_with_indifferent_access_test.rb
+++ b/activesupport/test/hash_with_indifferent_access_test.rb
@@ -7,4 +7,11 @@ class HashWithIndifferentAccessTest < ActiveSupport::TestCase
     hash.reverse_merge! key: :new_value
     assert_equal :old_value, hash[:key]
   end
+
+  def test_frozen_value
+    value = [1, 2, 3].freeze
+    hash = {}.with_indifferent_access
+    hash[:key] = value
+    assert_equal hash[:key], value
+  end
 end
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