Warn for calling public/protected/private/module_function without arguments inside method

Calling these methods without an argument does not have the
desired effect inside a method.

Fixes [Bug #13249]

test/ruby/test_class.rb

@@ -131,6 +131,48 @@ class TestClass < Test::Unit::TestCase
       [:module_function, :extend_object, :append_features, :prepend_features])
   end
 
+  def test_visibility_inside_method
+    assert_warn(/calling private without arguments inside a method may not have the intended effect/, '[ruby-core:79751]') do
+      Class.new do
+        def self.foo
+          private
+        end
+        foo
+      end
+    end
+
+    assert_warn(/calling protected without arguments inside a method may not have the intended effect/, '[ruby-core:79751]') do
+      Class.new do
+        def self.foo
+          protected
+        end
+        foo
+      end
+    end
+
+    assert_warn(/calling public without arguments inside a method may not have the intended effect/, '[ruby-core:79751]') do
+      Class.new do
+        def self.foo
+          public
+        end
+        foo
+      end
+    end
+
+    assert_warn(/calling private without arguments inside a method may not have the intended effect/, '[ruby-core:79751]') do
+      Class.new do
+        class << self
+          alias priv private
+        end
+
+        def self.foo
+          priv
+        end
+        foo
+      end
+    end
+  end
+
   def test_method_redefinition
     feature2155 = '[ruby-dev:39400]'
 

test/ruby/test_module.rb

@@ -1394,6 +1394,17 @@ class TestModule < Test::Unit::TestCase
     assert_match(/: warning: previous definition of foo/, stderr)
   end
 
+  def test_module_function_inside_method
+    assert_warn(/calling module_function without arguments inside a method may not have the intended effect/, '[ruby-core:79751]') do
+      Module.new do
+        def self.foo
+          module_function
+        end
+        foo
+      end
+    end
+  end
+
   def test_protected_singleton_method
     klass = Class.new
     x = klass.new

vm_method.c

@@ -1126,9 +1126,21 @@ rb_scope_visibility_set(rb_method_visibility_t visi)
     vm_cref_set_visibility(visi, FALSE);
 }
 
+static void
+scope_visibility_check(void)
+{
+    /* Check for public/protected/private/module_function called inside a method */
+    rb_control_frame_t *cfp = rb_current_execution_context()->cfp+1;
+    if (cfp && cfp->iseq && cfp->iseq->body->type == ISEQ_TYPE_METHOD) {
+        rb_warn("calling %s without arguments inside a method may not have the intended effect",
+            rb_id2name(rb_frame_this_func()));
+    }
+}
+
 static void
 rb_scope_module_func_set(void)
 {
+    scope_visibility_check();
     vm_cref_set_visibility(METHOD_VISI_PRIVATE, TRUE);
 }
 
@@ -1663,7 +1675,8 @@ static VALUE
 set_visibility(int argc, const VALUE *argv, VALUE module, rb_method_visibility_t visi)
 {
     if (argc == 0) {
-	rb_scope_visibility_set(visi);
+        scope_visibility_check();
+        rb_scope_visibility_set(visi);
     }
     else {
 	set_method_visibility(module, argc, argv, visi);