add Kernel#respond_to_missing?

core/kernel.rbs

@@ -2806,6 +2806,23 @@ module Kernel : BasicObject
   #
   def respond_to?: (interned name, ?boolish include_all) -> bool
 
+  # <!--
+  #   rdoc-file=vm_method.c
+  #   - obj.respond_to_missing?(symbol, include_all) -> true or false
+  #   - obj.respond_to_missing?(string, include_all) -> true or false
+  # -->
+  # DO NOT USE THIS DIRECTLY.
+  #
+  # Hook method to return whether the *obj* can respond to *id* method or not.
+  #
+  # When the method name parameter is given as a string, the string is converted
+  # to a symbol.
+  #
+  # See #respond_to?, and the example of BasicObject.
+  #
+  %a{annotate:rdoc:copy:Object#respond_to_missing?}
+  private def respond_to_missing?: (Symbol, bool) -> bool
+
   # <!--
   #   rdoc-file=vm_eval.c
   #   - foo.send(symbol [, args...])       -> obj

test/stdlib/Kernel_test.rb

@@ -941,4 +941,15 @@ def test_define_singleton_method
       Object.instance_method(:to_s)
     )
   end
+
+  def test_respond_to_missing?
+    obj = Object.new
+
+    # The default implementation always returns `false` regardless of the args,
+    # let alone their types; though overrides only have to support Symbol + bool
+    assert_send_type(
+      "(::Symbol, bool) -> bool",
+      obj, :respond_to_missing?, :to_s, true
+    )
+  end
 end