1 files changed, 36 insertions, 0 deletions
diff --git a/lib/prism/polyfill/warn.rb b/lib/prism/polyfill/warn.rb
new file mode 100644
index 0000000000..76a4264623
--- /dev/null
+++ b/lib/prism/polyfill/warn.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# Polyfill for Kernel#warn with the category parameter. Not all Ruby engines
+# have Method#parameters implemented, so we check the arity instead if
+# necessary.
+if (method = Kernel.instance_method(:warn)).respond_to?(:parameters) ? method.parameters.none? { |_, name| name == :category } : (method.arity == -1)
+  Kernel.prepend(
+    Module.new {
+      def warn(*msgs, uplevel: nil, category: nil) # :nodoc:
+        case uplevel
+        when nil
+          super(*msgs)
+        when Integer
+          super(*msgs, uplevel: uplevel + 1)
+        else
+          super(*msgs, uplevel: uplevel.to_int + 1)
+        end
+      end
+    }
+  )
+
+  Object.prepend(
+    Module.new {
+      def warn(*msgs, uplevel: nil, category: nil) # :nodoc:
+        case uplevel
+        when nil
+          super(*msgs)
+        when Integer
+          super(*msgs, uplevel: uplevel + 1)
+        else
+          super(*msgs, uplevel: uplevel.to_int + 1)
+        end
+      end
+    }
+  )
+end