[ruby/prism] Handle stovetop start in constant path fullname

https://github.com/ruby/prism/commit/3a216e63fe

lib/prism/node_ext.rb

@@ -118,7 +118,7 @@ module Prism
         current = current.parent
       end
 
-      unless current.is_a?(ConstantReadNode)
+      unless current.is_a?(ConstantReadNode) || current == nil
         raise DynamicPartsInConstantPathError, "Constant path contains dynamic parts. Cannot compute full name"
       end
 

test/prism/constant_path_node_test.rb

@@ -52,5 +52,16 @@ module Prism
       node = Prism.parse(source).value.statements.body.first
       assert_equal("Foo::Bar::Baz::Qux", node.lefts.first.full_name)
     end
+
+    def test_full_name_for_constant_path_with_stovetop_start
+      source = <<~RUBY
+        ::Foo:: # comment
+          Bar::Baz::
+            Qux, Something = [1, 2]
+      RUBY
+
+      node = Prism.parse(source).value.statements.body.first
+      assert_equal("::Foo::Bar::Baz::Qux", node.lefts.first.full_name)
+    end
   end
 end