* numeric.c (do_coerce): Add a warning when an exception is raised

or an invalid value is returned in #coerce called by
  numeric comparison operators and the exception
  thrown by the caller has no information on the failure.
  In the next release such exception should not be rescued or
  should be the cause of the caller exception. nil is accepted
  as the "no possible coercion" return value. See #7688.
* test/ruby/test_numeric.rb: Add corresponding test.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46375 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,15 @@
+Sat Jun  7 22:13:42 2014  Benoit Daloze  <eregontp@gmail.com>
+
+	* numeric.c (do_coerce): Add a warning when an exception is raised
+	  or an invalid value is returned in #coerce called by
+	  numeric comparison operators and the exception
+	  thrown by the caller has no information on the failure.
+	  In the next release such exception should not be rescued or
+	  should be the cause of the caller exception. nil is accepted
+	  as the "no possible coercion" return value. See #7688.
+
+	* test/ruby/test_numeric.rb: Add corresponding test.
+
 Sat Jun  7 18:15:33 2014  Benoit Daloze  <eregontp@gmail.com>
 
 	* numeric.c (bit_coerce): remove constant parameter `err'

numeric.c

@@ -251,6 +251,12 @@ coerce_rescue(VALUE *x)
     return Qnil;		/* dummy */
 }
 
+static VALUE
+coerce_rescue_quiet(VALUE *x)
+{
+    return Qundef;
+}
+
 static int
 do_coerce(VALUE *x, VALUE *y, int err)
 {
@@ -266,10 +272,18 @@ do_coerce(VALUE *x, VALUE *y, int err)
 	return FALSE;
     }
 
-    ary = rb_rescue(coerce_body, (VALUE)a, err ? coerce_rescue : 0, (VALUE)a);
+    ary = rb_rescue(coerce_body, (VALUE)a, err ? coerce_rescue : coerce_rescue_quiet, (VALUE)a);
+    if (ary == Qundef) {
+	rb_warn("Numerical comparison operators will no more rescue exceptions of #coerce");
+	rb_warn("in the next release. Return nil in #coerce if the coercion is impossible.");
+	return FALSE;
+    }
     if (!RB_TYPE_P(ary, T_ARRAY) || RARRAY_LEN(ary) != 2) {
 	if (err) {
 	    rb_raise(rb_eTypeError, "coerce must return [x, y]");
+	} else if (!NIL_P(ary)) {
+	    rb_warn("Bad return value for #coerce, called by numerical comparison operators.");
+	    rb_warn("#coerce must return [x, y]. The next release will raise an error for this.");
 	}
 	return FALSE;
     }

test/ruby/test_numeric.rb

@@ -59,6 +59,23 @@ class TestNumeric < Test::Unit::TestCase
     end
     assert_equal(-1, -a)
 
+    bug7688 = '[ruby-core:51389] [Bug #7688]'
+    DummyNumeric.class_eval do
+      remove_method :coerce
+      def coerce(x); raise StandardError; end
+    end
+    assert_raise_with_message(TypeError, /can't be coerced into /) { 1 + a }
+    warn = /will no more rescue exceptions of #coerce.+ in the next release/m
+    assert_warn(warn, bug7688) { assert_raise(ArgumentError) { 1 < a } }
+
+    DummyNumeric.class_eval do
+      remove_method :coerce
+      def coerce(x); :bad_return_value; end
+    end
+    assert_raise_with_message(TypeError, "coerce must return [x, y]") { 1 + a }
+    warn = /Bad return value for #coerce.+next release will raise an error/m
+    assert_warn(warn, bug7688) { assert_raise(ArgumentError) { 1 < a } }
+
   ensure
     DummyNumeric.class_eval do
       remove_method :coerce