Fix Column deduplication leaking virtual? across tables

lib/active_record/connection_adapters/clickhouse/column.rb

@@ -21,6 +21,21 @@ def virtual?
           default_kind.materialized? || default_kind.alias?
         end
 
+        # Base Column equality ignores our extra attributes, so ActiveRecord's
+        # deduplication registry would intern a plain column and a MATERIALIZED
+        # column of the same name/type as one object — leaking virtual? onto
+        # the plain column and silently dropping it from INSERTs.
+        def ==(other)
+          super &&
+            other.respond_to?(:default_kind) && default_kind.to_s == other.default_kind.to_s &&
+            other.respond_to?(:codec) && codec == other.codec
+        end
+        alias eql? ==
+
+        def hash
+          [super, default_kind.to_s, codec].hash
+        end
+
         private
 
         def deduplicated

spec/single/column_dedup_spec.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+RSpec.describe ActiveRecord::ConnectionAdapters::Clickhouse::Column do
+  def build_column(default_kind: nil, codec: nil)
+    metadata = ActiveRecord::ConnectionAdapters::SqlTypeMetadata.new(
+      sql_type: 'String', type: :string
+    )
+    args = ['city_name']
+    args << ActiveModel::Type::String.new if ActiveRecord.version >= Gem::Version.new('8.1')
+    args += [nil, metadata, false, nil]
+    described_class.new(*args, codec: codec, default_kind: default_kind)
+  end
+
+  it 'does not treat a materialized column as equal to a plain column' do
+    plain = build_column
+    materialized = build_column(default_kind: 'MATERIALIZED')
+
+    expect(plain).not_to eq(materialized)
+    expect(plain.hash).not_to eq(materialized.hash)
+  end
+
+  it 'does not deduplicate a plain column into a materialized column' do
+    materialized = build_column(default_kind: 'MATERIALIZED').deduplicate
+    plain = build_column.deduplicate
+
+    expect(plain).not_to be_virtual
+    expect(plain).not_to equal(materialized)
+  end
+
+  it 'treats identical columns as equal' do
+    expect(build_column).to eq(build_column)
+    expect(build_column.hash).to eq(build_column.hash)
+  end
+
+  it 'does not treat columns with different codecs as equal' do
+    expect(build_column(codec: 'ZSTD')).not_to eq(build_column)
+  end
+end