reserve index name chars for internal rails operations

Some adapter (SQLite3) need to perform renaming operations to support
the rails DDL. These rename prefixes operate with prefixes. When an
index name already uses up the full space provieded by
`index_name_length` these internal operations will fail. This patch
introduces `allowed_index_name_length` which respects the amount of
characters used for internal operations. It will always be <=
`index_name_length` and every adapter can define how many characters
need to be reserved.

2 files changed, 34 insertions, 5 deletions

diff --git a/activerecord/test/cases/migration/index_test.rb b/activerecord/test/cases/migration/index_test.rb
index a41f2c10f0..5df9a5342d 100644
--- a/activerecord/test/cases/migration/index_test.rb
+++ b/activerecord/test/cases/migration/index_test.rb
@@ -55,19 +55,31 @@ module ActiveRecord
         assert_raise(ArgumentError) { connection.remove_index(table_name, "no_such_index") }
       end
 
-      def test_add_index_name_length_limit
-        good_index_name = 'x' * connection.index_name_length
+      def test_add_index_works_with_long_index_names
+        connection.add_index(table_name, "foo", name: good_index_name)
+
+        assert connection.index_name_exists?(table_name, good_index_name, false)
+        connection.remove_index(table_name, name: good_index_name)
+      end
+
+      def test_add_index_does_not_accept_too_long_index_names
         too_long_index_name = good_index_name + 'x'
 
-        assert_raises(ArgumentError) {
-          connection.add_index(table_name, "foo", :name => too_long_index_name)
+        e = assert_raises(ArgumentError) {
+          connection.add_index(table_name, "foo", name: too_long_index_name)
         }
+        assert_match /too long; the limit is #{connection.allowed_index_name_length} characters/, e.message
 
         assert_not connection.index_name_exists?(table_name, too_long_index_name, false)
         connection.add_index(table_name, "foo", :name => good_index_name)
+      end
+
+      def test_internal_index_with_name_matching_database_limit
+        good_index_name = 'x' * connection.index_name_length
+        connection.add_index(table_name, "foo", name: good_index_name, internal: true)
 
         assert connection.index_name_exists?(table_name, good_index_name, false)
-        connection.remove_index(table_name, :name => good_index_name)
+        connection.remove_index(table_name, name: good_index_name)
       end
 
       def test_index_symbol_names
@@ -196,6 +208,12 @@ module ActiveRecord
         connection.remove_index("testings", "last_name")
         assert !connection.index_exists?("testings", "last_name")
       end
+
+      private
+        def good_index_name
+          'x' * connection.allowed_index_name_length
+        end
+
     end
   end
 end
diff --git a/activerecord/test/cases/migration/rename_column_test.rb b/activerecord/test/cases/migration/rename_column_test.rb
index 8f6918d06a..b116753d04 100644
--- a/activerecord/test/cases/migration/rename_column_test.rb
+++ b/activerecord/test/cases/migration/rename_column_test.rb
@@ -197,6 +197,17 @@ module ActiveRecord
         assert_equal ['test_models_categories_idx'], connection.indexes('test_models').map(&:name)
       end
 
+      def test_change_column_with_long_index_name
+        table_name_prefix = 'test_models_'
+        long_index_name = table_name_prefix + ('x' * (connection.allowed_index_name_length - table_name_prefix.length))
+        add_column "test_models", "category", :string
+        add_index :test_models, :category, name: long_index_name
+
+        change_column "test_models", "category", :string, null: false, default: 'article'
+
+        assert_equal [long_index_name], connection.indexes('test_models').map(&:name)
+      end
+
       def test_change_column_default
         add_column "test_models", "first_name", :string
         connection.change_column_default "test_models", "first_name", "Tester"