Correctly handle array columns with defaults in the schema dumper

If the subtype provides custom schema dumping behavior, we need to defer
to it. We purposely choose not to handle any values other than an array
(which technically should only ever be `nil`, but I'd rather code
defensively here).

Fixes #20515.

4 files changed, 17 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 02b2096ef6..34e760e527 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Correctly handle decimal arrays with defaults in the schema dumper.
+
+    Fixes #20515.
+
+    *Sean Griffin*
+
 *   Deprecate the PG `:point` type in favor of a new one which will return
     `Point` objects instead of an `Array`
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
index 3de794f797..25961a9869 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
@@ -45,6 +45,11 @@ module ActiveRecord
               delimiter == other.delimiter
           end
 
+          def type_cast_for_schema(value)
+            return super unless value.is_a?(::Array)
+            "[" + value.map { |v| subtype.type_cast_for_schema(v) }.join(", ") + "]"
+          end
+
           private
 
           def type_cast_array(value, method)
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index e6f0fe6f75..51170c533b 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -253,6 +253,11 @@ class SchemaDumperTest < ActiveRecord::TestCase
       assert_match %r{t\.integer\s+"big_int_data_points\",\s+limit: 8,\s+array: true}, output
     end
 
+    def test_schema_dump_allows_array_of_decimal_defaults
+      output = standard_dump
+      assert_match %r{t\.decimal\s+"decimal_array_default",\s+default: \[1.23, 3.45\],\s+array: true}, output
+    end
+
     if ActiveRecord::Base.connection.supports_extensions?
       def test_schema_dump_includes_extensions
         connection = ActiveRecord::Base.connection
diff --git a/activerecord/test/schema/postgresql_specific_schema.rb b/activerecord/test/schema/postgresql_specific_schema.rb
index 872fa595b4..df0362573b 100644
--- a/activerecord/test/schema/postgresql_specific_schema.rb
+++ b/activerecord/test/schema/postgresql_specific_schema.rb
@@ -107,5 +107,6 @@ _SQL
 
   create_table :bigint_array, force: true do |t|
     t.integer :big_int_data_points, limit: 8, array: true
+    t.decimal :decimal_array_default, array: true, default: [1.23, 3.45]
   end
 end