Move establish_connection to handler

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

@@ -837,7 +837,15 @@ def connection_pool_list
       end
       alias :connection_pools :connection_pool_list
 
-      def establish_connection(spec)
+      def establish_connection(spec_or_config, name: "primary")
+        if spec_or_config.is_a?(ConnectionSpecification)
+          spec = spec_or_config
+        else
+          resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(ActiveRecord::Base.configurations)
+          spec = resolver.spec(spec_or_config, name)
+        end
+
+        remove_connection(spec.name)
         owner_to_pool[spec.name] = ConnectionAdapters::ConnectionPool.new(spec)
       end
 

activerecord/lib/active_record/connection_adapters/connection_specification.rb

@@ -180,6 +180,10 @@ def spec(config, name = nil)
 
           adapter_method = "#{spec[:adapter]}_connection"
 
+          unless ActiveRecord::Base.respond_to?(adapter_method)
+            raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter"
+          end
+
           name ||=
             if config.is_a?(Symbol)
               config.to_s

activerecord/lib/active_record/connection_handling.rb

@@ -44,21 +44,13 @@ module ConnectionHandling
     #
     # The exceptions AdapterNotSpecified, AdapterNotFound and +ArgumentError+
     # may be returned on an error.
-    def establish_connection(spec = nil)
+    def establish_connection(config = nil)
       raise "Anonymous class is not allowed." unless name
 
-      spec     ||= DEFAULT_ENV.call.to_sym
-      resolver =   ConnectionAdapters::ConnectionSpecification::Resolver.new configurations
-      # TODO: uses name on establish_connection, for backwards compatibility
-      spec     =   resolver.spec(spec, self == Base ? "primary" : name)
-
-      unless respond_to?(spec.adapter_method)
-        raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter"
-      end
-
-      remove_connection(spec.name)
-      self.connection_specification_name = spec.name
-      connection_handler.establish_connection spec
+      config ||= DEFAULT_ENV.call.to_sym
+      spec_name = self == Base ? "primary" : name
+      self.connection_specification_name = spec_name
+      connection_handler.establish_connection(config, name: spec_name)
     end
 
     class MergeAndResolveDefaultUrlConfig # :nodoc: