Don't choke when change_table temporal: true on a table with computed…

… indexes (fixes #99)

lib/chrono_model/adapter/indexes.rb

@@ -136,9 +136,14 @@ def chrono_copy_indexes_to_history(table_name)
             next if history_indexes.include?(index.name)
 
             on_history_schema do
+              # index.columns is an Array for plain indexes,
+              # while it is a String for computed indexes.
+              #
+              columns = Array.wrap(index.columns).join(', ')
+
               execute %[
                 CREATE INDEX #{index.name} ON #{table_name}
-                USING #{index.using} ( #{index.columns.join(', ')} )
+                USING #{index.using} ( #{columns} )
               ], 'Copy index from temporal to history'
             end
           end

spec/chrono_model/adapter/migrations_spec.rb

@@ -1,6 +1,8 @@
 require 'spec_helper'
 require 'support/adapter/structure'
 
+# For the structure of these tables, please see spec/support/adabters/structure.rb.
+#
 shared_examples_for 'temporal table' do
   it { expect(adapter.is_chrono?(subject)).to be(true) }
 
@@ -94,12 +96,18 @@
       before :all do
         adapter.add_index table, :foo
         adapter.add_index table, :bar, :unique => true
+        adapter.add_index table, '(lower(baz))'
+        adapter.add_index table, '(lower(baz) || upper(baz))'
 
         adapter.change_table table, :temporal => true
       end
 
       it_should_behave_like 'temporal table'
 
+      let(:temporal_indexes) do
+        adapter.indexes(table)
+      end
+
       let(:history_indexes) do
         adapter.on_schema(ChronoModel::Adapter::HISTORY_SCHEMA) do
           adapter.indexes(table)
@@ -113,6 +121,19 @@
       it "copies unique index to history without uniqueness constraint" do
         expect(history_indexes.find {|i| i.columns == ['bar'] && i.unique == false}).to be_present
       end
+
+      it 'copies also computed indexes' do
+        indexes = %W(
+          index_#{table}_on_bar
+          index_#{table}_on_foo
+          index_#{table}_on_lower_baz
+          index_#{table}_on_lower_baz_upper_baz
+        )
+
+        expect(temporal_indexes.map(&:name).sort).to eq(indexes)
+
+        expect(indexes - history_indexes.map(&:name).sort).to be_empty
+      end
     end
 
     with_plain_table do