YAML: allow using disciminator in contained types (crystal-lang#9851)

spec/std/yaml/serializable_spec.cr

@@ -304,6 +304,12 @@ class YAMLCircle < YAMLShape
   property radius : Int32
 end
 
+class YAMLWithShape
+  include YAML::Serializable
+
+  property shape : YAMLShape
+end
+
 describe "YAML::Serializable" do
   it "works with record" do
     YAMLAttrPoint.new(1, 2).to_yaml.should eq "---\nx: 1\ny: 2\n"
@@ -831,5 +837,12 @@ describe "YAML::Serializable" do
         YAMLShape.from_yaml(%({"type": "unknown"}))
       end
     end
+
+    it "deserializes type which nests type with discriminator (#9849)" do
+      container = YAMLWithShape.from_yaml(%({"shape": {"type": "point", "x": 1, "y": 2}}))
+      point = container.shape.as(YAMLPoint)
+      point.x.should eq(1)
+      point.y.should eq(2)
+    end
   end
 end

src/yaml/serialization.cr

@@ -381,7 +381,7 @@ module YAML
         {% mapping.raise "mapping argument must be a HashLiteral or a NamedTupleLiteral, not #{mapping.class_name.id}" %}
       {% end %}
 
-      private def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
+      def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
         ctx.read_alias(node, \{{@type}}) do |obj|
           return obj
         end