SQLite: Fix `copy_table` with composite primary keys

`connection.primary_key` also return composite primary keys, so
`from_primary_key_column` may not be found even if `from_primary_key` is
presented.

```
% ARCONN=sqlite3 be ruby -w -Itest
test/cases/adapters/sqlite3/sqlite3_adapter_test.rb -n
test_copy_table_with_composite_primary_keys
Using sqlite3
Run options: -n test_copy_table_with_composite_primary_keys --seed 19041

# Running:

E

Error:
ActiveRecord::ConnectionAdapters::SQLite3AdapterTest#test_copy_table_with_composite_primary_keys:
NoMethodError: undefined method `type' for nil:NilClass
    /path/to/rails/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb:411:in
    `block in copy_table'
```

This change fixes `copy_table` to do not lose composite primary keys.

1 files changed, 29 insertions, 2 deletions

diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
index 14f4997d5b..1357719422 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
@@ -361,21 +361,48 @@ module ActiveRecord
       end
 
       class Barcode < ActiveRecord::Base
+        self.primary_key = "code"
       end
 
-      def test_existing_records_have_custom_primary_key
+      def test_copy_table_with_existing_records_have_custom_primary_key
         connection = Barcode.connection
         connection.create_table(:barcodes, primary_key: "code", id: :string, limit: 42, force: true) do |t|
           t.text :other_attr
         end
         code = "214fe0c2-dd47-46df-b53b-66090b3c1d40"
-        Barcode.create! code: code, other_attr: "xxx"
+        Barcode.create!(code: code, other_attr: "xxx")
 
         connection.change_table "barcodes" do |t|
           connection.remove_column("barcodes", "other_attr")
         end
 
         assert_equal code, Barcode.first.id
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_copy_table_with_composite_primary_keys
+        connection = Barcode.connection
+        connection.create_table(:barcodes, primary_key: ["region", "code"], force: true) do |t|
+          t.string :region
+          t.string :code
+          t.text :other_attr
+        end
+        region = "US"
+        code = "214fe0c2-dd47-46df-b53b-66090b3c1d40"
+        Barcode.create!(region: region, code: code, other_attr: "xxx")
+
+        connection.change_table "barcodes" do |t|
+          connection.remove_column("barcodes", "other_attr")
+        end
+
+        assert_equal ["region", "code"], connection.primary_keys("barcodes")
+
+        barcode = Barcode.first
+        assert_equal region, barcode.region
+        assert_equal code, barcode.code
+      ensure
+        Barcode.reset_column_information
       end
 
       def test_supports_extensions