Fix element type inference in YAML::ArrayConverter.from_yaml (#16166)

Author: HertzDevil

spec/std/yaml/serializable_spec.cr

@@ -148,6 +148,23 @@ class YAMLAttrWithTimeArray3
   property value : Array(Time)
 end
 
+module YAMLAttrPointConverter
+  def self.from_yaml(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
+    YAMLAttrPoint.new(ctx, node)
+  end
+
+  def self.to_yaml(value, yaml : YAML::Nodes::Builder)
+    value.to_yaml(yaml)
+  end
+end
+
+class YAMLAttrWithSerializableArray
+  include YAML::Serializable
+
+  @[YAML::Field(converter: YAML::ArrayConverter(YAMLAttrPointConverter))]
+  property value : Array(YAMLAttrPoint)
+end
+
 class YAMLAttrWithSimpleMapping
   include YAML::Serializable
 
@@ -986,6 +1003,14 @@ describe "YAML::Serializable" do
       yaml.value.map(&.to_s).should eq(["2014-10-31 23:37:16 UTC"])
       yaml.to_yaml.should eq(string)
     end
+
+    it "uses correct array element type" do
+      string = %(---\nvalue:\n- x: 1\n  y: 2\n)
+      yaml = YAMLAttrWithSerializableArray.from_yaml(string)
+      yaml.value.should be_a(Array(YAMLAttrPoint))
+      yaml.value.should eq([YAMLAttrPoint.new(1, 2)])
+      yaml.to_yaml.should eq(string)
+    end
   end
 
   it "parses nilable union" do

src/yaml/from_yaml.cr

@@ -376,7 +376,10 @@ module YAML::ArrayConverter(Converter)
         node.raise "Expected sequence, not #{node.kind}"
       end
 
-      ary = Array(typeof(@converter.from_yaml(ctx, node))).new
+      ary = Array(typeof(begin
+        value = uninitialized YAML::Nodes::Node
+        @converter.from_yaml(ctx, value)
+      end)).new
 
       node.each do |value|
         ary << @converter.from_yaml(ctx, value)