Fix test failures when prepared statements are disabled

This also reverts the change to enable prepared statements by default on
MySQL (though I suspect we could enable them and it'd be great). This
change brings back a collector closer to the old `Bind` collector in
Arel. However, this one lives in AR, since this is an AR specific need.
Additionally, we only use it for statement caching, since the new
substitute collector in Arel is higher performance for most cases.

activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb

@@ -29,8 +29,9 @@ def cacheable_query(klass, arel) # :nodoc:
           sql, binds = visitor.accept(arel.ast, collector).value
           query = klass.query(sql)
         else
-          query = klass.partial_query(arel.ast)
-          binds = []
+          collector = PartialQueryCollector.new
+          parts, binds = visitor.accept(arel.ast, collector).value
+          query = klass.partial_query(parts)
         end
         [query, binds]
       end
@@ -457,6 +458,28 @@ def with_yaml_fallback(value)
             value
           end
         end
+
+        class PartialQueryCollector
+          def initialize
+            @parts = []
+            @binds = []
+          end
+
+          def << str
+            @parts << str
+            self
+          end
+
+          def add_bind obj
+            @binds << obj
+            @parts << Arel::Nodes::BindParam.new(1)
+            self
+          end
+
+          def value
+            [@parts, @binds]
+          end
+        end
     end
   end
 end

activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb

@@ -39,7 +39,7 @@ class Mysql2Adapter < AbstractMysqlAdapter
 
       def initialize(connection, logger, connection_options, config)
         super
-        @prepared_statements = true unless config[:prepared_statements] == false
+        @prepared_statements = false unless config.key?(:prepared_statements)
         configure_connection
       end
 

activerecord/lib/active_record/statement_cache.rb

@@ -41,20 +41,18 @@ def sql_for(binds, connection)
     end
 
     class PartialQuery < Query # :nodoc:
-      def initialize(arel)
-        @arel = arel
+      def initialize(values)
+        @values = values
+        @indexes = values.each_with_index.find_all { |thing, i|
+          Arel::Nodes::BindParam === thing
+        }.map(&:last)
       end
 
       def sql_for(binds, connection)
-        val = @arel.dup
-        val.grep(Arel::Nodes::BindParam) do |node|
-          node.value = binds.shift
-          if binds.empty?
-            break
-          end
-        end
-        sql, _ = connection.visitor.accept(val, connection.send(:collector)).value
-        sql
+        val = @values.dup
+        casted_binds = binds.map(&:value_for_database)
+        @indexes.each { |i| val[i] = connection.quote(casted_binds.shift) }
+        val.join
       end
     end