From 44c5c2a3120439af7560f9694dcb117953ee3119 Mon Sep 17 00:00:00 2001
From: nobu <nobu@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Sun, 17 Feb 2013 11:55:50 +0000
Subject: compar.c: inversed comarison without infinite recursion

* compar.c (rb_invcmp): compare by inversed comarison, with preventing
  from infinite recursion.  [ruby-core:52305] [Bug #7870]
* string.c (rb_str_cmp_m), time.c (time_cmp): get rid of infinite
  recursion.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39292 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
---
 ChangeLog                    |  8 ++++++++
 compar.c                     | 20 ++++++++++++++++++++
 internal.h                   |  3 +++
 string.c                     |  7 +------
 test/ruby/test_comparable.rb |  7 +++++++
 time.c                       |  7 +------
 6 files changed, 40 insertions(+), 12 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 84fd20732b..ddea0a1c18 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Sun Feb 17 20:55:44 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* compar.c (rb_invcmp): compare by inversed comarison, with preventing
+	  from infinite recursion.  [ruby-core:52305] [Bug #7870]
+
+	* string.c (rb_str_cmp_m), time.c (time_cmp): get rid of infinite
+	  recursion.
+
 Sun Feb 17 17:23:22 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/mkmf.rb: remove extra topdir in VPATH, which was in
diff --git a/compar.c b/compar.c
index 6762786276..c89c752daf 100644
--- a/compar.c
+++ b/compar.c
@@ -31,6 +31,26 @@ rb_cmperr(VALUE x, VALUE y)
 	     rb_obj_classname(x), classname);
 }
 
+static VALUE
+invcmp_recursive(VALUE x, VALUE y, int recursive)
+{
+    if (recursive) return Qnil;
+    return rb_check_funcall(y, cmp, 1, &x);
+}
+
+VALUE
+rb_invcmp(VALUE x, VALUE y)
+{
+    VALUE invcmp = rb_exec_recursive(invcmp_recursive, x, y);
+    if (invcmp == Qundef || NIL_P(invcmp)) {
+	return Qnil;
+    }
+    else {
+	int result = -rb_cmpint(invcmp, x, y);
+	return INT2FIX(result);
+    }
+}
+
 static VALUE
 cmp_eq(VALUE *a)
 {
diff --git a/internal.h b/internal.h
index 971d6bde87..8630b8bbf3 100644
--- a/internal.h
+++ b/internal.h
@@ -66,6 +66,9 @@ VALUE rb_special_singleton_class(VALUE);
 VALUE rb_singleton_class_clone_and_attach(VALUE obj, VALUE attach);
 void Init_class_hierarchy(void);
 
+/* compar.c */
+VALUE rb_invcmp(VALUE, VALUE);
+
 /* compile.c */
 int rb_dvar_defined(ID);
 int rb_local_defined(ID);
diff --git a/string.c b/string.c
index 017617aaf1..3d4fd37b5a 100644
--- a/string.c
+++ b/string.c
@@ -2389,13 +2389,8 @@ rb_str_cmp_m(VALUE str1, VALUE str2)
 	if (RB_TYPE_P(tmp, T_STRING)) {
 	    result = rb_str_cmp(str1, tmp);
 	}
-	else if ((tmp = rb_check_funcall(str2, rb_intern("<=>"), 1, &str1)) ==
-		 Qundef) {
-	    return Qnil;
-	}
 	else {
-	    if (NIL_P(tmp)) return Qnil;
-	    result = -rb_cmpint(tmp, str1, str2);
+	    return rb_invcmp(str1, str2);
 	}
     }
     else {
diff --git a/test/ruby/test_comparable.rb b/test/ruby/test_comparable.rb
index 00ce6b485a..c686adeceb 100644
--- a/test/ruby/test_comparable.rb
+++ b/test/ruby/test_comparable.rb
@@ -69,4 +69,11 @@ class TestComparable < Test::Unit::TestCase
     assert_raise(ArgumentError) { 1.0 < nil }
     assert_raise(ArgumentError) { 1.0 < Object.new }
   end
+
+  def test_inversed_compare
+    bug7870 = '[ruby-core:52305] [Bug #7870]'
+    assert_nothing_raised(SystemStackError, bug7870) {
+      assert_nil(Time.new <=> "")
+    }
+  end
 end
diff --git a/time.c b/time.c
index 29565be6e2..765dc31194 100644
--- a/time.c
+++ b/time.c
@@ -3365,12 +3365,7 @@ time_cmp(VALUE time1, VALUE time2)
 	n = wcmp(tobj1->timew, tobj2->timew);
     }
     else {
-	VALUE tmp;
-
-	tmp = rb_funcall(time2, rb_intern("<=>"), 1, time1);
-	if (NIL_P(tmp)) return Qnil;
-
-	n = -rb_cmpint(tmp, time1, time2);
+	return rb_invcmp(time1, time2);
     }
     if (n == 0) return INT2FIX(0);
     if (n > 0) return INT2FIX(1);
-- 
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