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.

1 files changed, 8 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 91444950be..1b93af5033 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -187,6 +187,13 @@ module ActiveRecord
         true
       end
 
+      # Returns 51. SQLite supports index names up to 64
+      # characters. The rest is used by rails internally to perform
+      # temporary rename operations
+      def allowed_index_name_length
+        index_name_length - 13
+      end
+
       def native_database_types #:nodoc:
         {
           :primary_key => default_primary_key_type,
@@ -559,7 +566,7 @@ module ActiveRecord
 
             unless columns.empty?
               # index name can't be the same
-              opts = { name: name.gsub(/(^|_)(#{from})_/, "\\1#{to}_") }
+              opts = { name: name.gsub(/(^|_)(#{from})_/, "\\1#{to}_"), internal: true }
               opts[:unique] = true if index.unique
               add_index(to, columns, opts)
             end