signal.c: SIGEXIT is not a system signal

* signal.c (trap): SIGEXIT is not a system signal and is dealt
  with internally, so it should not try to register the system
  signal handler by sigaction.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47669 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

signal.c

@@ -1089,8 +1089,13 @@ trap(int sig, sighandler_t func, VALUE command)
      * atomically. In current implementation, we only need to don't call
      * RUBY_VM_CHECK_INTS().
      */
+    if (sig == 0) {
+	oldfunc = SIG_ERR;
+    }
+    else {
 	oldfunc = ruby_signal(sig, func);
 	if (oldfunc == SIG_ERR) rb_sys_fail_str(rb_signo2signm(sig));
+    }
     oldcmd = vm->trap_list[sig].cmd;
     switch (oldcmd) {
       case 0:

test/ruby/test_signal.rb

@@ -177,6 +177,14 @@ class TestSignal < Test::Unit::TestCase
     end
   end
 
+  def test_sigexit
+    assert_in_out_err([], 'Signal.trap(:EXIT) {print "OK"}', ["OK"])
+    assert_in_out_err([], 'Signal.trap("EXIT") {print "OK"}', ["OK"])
+    assert_in_out_err([], 'Signal.trap(:SIGEXIT) {print "OK"}', ["OK"])
+    assert_in_out_err([], 'Signal.trap("SIGEXIT") {print "OK"}', ["OK"])
+    assert_in_out_err([], 'Signal.trap(0) {print "OK"}', ["OK"])
+  end
+
   def test_kill_immediately_before_termination
     Signal.list[sig = "USR1"] or sig = "INT"
     assert_in_out_err(["-e", <<-"end;"], "", %w"foo")