Fix signature for validate_prop_name (#2548)

* Fix signature for validate_prop_name

* Add test

* Use match?

gems/sorbet-runtime/lib/types/props/decorator.rb

@@ -237,9 +237,10 @@ def prop_validate_definition!(name, cls, rules, type)
     nil
   end
 
-  sig {params(name: Symbol).void}
+  # Used to validate both prop names and serialized forms
+  sig {params(name: T.any(Symbol, String)).void}
   private def validate_prop_name(name)
-    if name !~ /\A[A-Za-z_][A-Za-z0-9_-]*\z/
+    if !name.match?(/\A[A-Za-z_][A-Za-z0-9_-]*\z/)
       raise ArgumentError.new("Invalid prop name in #{@class.name}: #{name}")
     end
   end

gems/sorbet-runtime/test/types/props/serializable.rb

@@ -512,4 +512,16 @@ class NoPropsStruct < T::Struct
       assert_equal({}, NoPropsStruct.from_hash({}).serialize)
     end
   end
+
+  class CustomSerializedForm < T::Struct
+    prop :prop, String, name: 'something_custom'
+  end
+
+  describe 'custom serialized form' do
+    it 'round trips' do
+      hash = CustomSerializedForm.new(prop: 'foo').serialize
+      assert_equal({'something_custom' => 'foo'}, hash)
+      assert_equal('foo', CustomSerializedForm.from_hash(hash).prop)
+    end
+  end
 end