Add Warning.categories

Author: soutaro

core/warning.rbs

@@ -66,6 +66,14 @@ module Warning
   #
   def self.[]=: [T] (category, T flag) -> T
 
+  # <!--
+  #   rdoc-file=error.c
+  #   - categories  -> array
+  # -->
+  # Returns a list of the supported category symbols.
+  #
+  def self.categories: () -> Array[Symbol]
+
   # <!--
   #   rdoc-file=error.c
   #   - warn(msg, category: nil)  -> nil

test/stdlib/Warning_test.rb

@@ -33,6 +33,13 @@ def test_aset
     refute_send_type "(_ToSym, Rational) -> Rational",
         Warning, :[]=, ToSym.new(WARNING_CATEGORIES.first), 1r
   end
+
+  def test_categories
+    if_ruby("3.4"...) do
+      assert_send_type "() -> Array[Symbol]",
+                       Warning, :categories
+    end
+  end
 end
 
 class WarningTest < Test::Unit::TestCase