supporting any node in SelectManager#from

lib/arel/select_manager.rb

@@ -38,6 +38,10 @@ def exists
       Arel::Nodes::Exists.new @ast
     end
 
+    def as node, expr
+      Arel::Nodes::As.new node, expr
+    end
+
     def where_clauses
       if $VERBOSE
         warn "(#{caller.first}) where_clauses is deprecated and will be removed in arel 3.0.0 with no replacement"
@@ -86,10 +90,10 @@ def from table
       # from the AR tests.
 
       case table
-      when Nodes::SqlLiteral, Arel::Table
-        @ctx.source.left = table
       when Nodes::Join
         @ctx.source.right << table
+      else
+        @ctx.source.left = table
       end
 
       self

test/test_select_manager.rb

@@ -101,6 +101,23 @@ def test_join_sources
           manager.project table['id']
           manager.to_sql.must_be_like 'SELECT "users"."id" FROM users'
         end
+
+        it 'should support any ast' do
+          table   = Table.new :users
+          manager1 = Arel::SelectManager.new Table.engine
+
+          manager2 = Arel::SelectManager.new Table.engine
+          manager2.project(Arel.sql('*'))
+          manager2.from table
+
+          manager1.project Arel.sql('lol')
+          as = manager2.as manager2.grouping(manager2.ast), Arel.sql('omg')
+          manager1.from as
+
+          manager1.to_sql.must_be_like %{
+            SELECT lol FROM (SELECT * FROM "users" ) AS omg
+          }
+        end
       end
 
       describe 'having' do