Improve error message

ref [Bug #13761]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59452 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 3 insertions, 3 deletions

diff --git a/sprintf.c b/sprintf.c
index 0d685ddbaf..52771eb52a 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -521,7 +521,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 
 	for (t = p; t < end && *t != '%'; t++) ;
 	if (t + 1 == end) {
-	    rb_raise(rb_eArgError, "incomplete format specifier");
+	    rb_raise(rb_eArgError, "incomplete format specifier; use %%%% (double %%) instead");
 	}
 	PUSH(p, t - p);
 	if (coderange != ENC_CODERANGE_BROKEN && scanned < blen) {
diff --git a/test/ruby/test_sprintf.rb b/test/ruby/test_sprintf.rb
index df004305ec..b46f5189e2 100644
--- a/test/ruby/test_sprintf.rb
+++ b/test/ruby/test_sprintf.rb
@@ -425,11 +425,11 @@ class TestSprintf < Test::Unit::TestCase
   end
 
   def test_percent_sign_at_end
-    assert_raise_with_message(ArgumentError, "incomplete format specifier") do
+    assert_raise_with_message(ArgumentError, "incomplete format specifier; use %% (double %) instead") do
       sprintf("%")
     end
 
-    assert_raise_with_message(ArgumentError, "incomplete format specifier") do
+    assert_raise_with_message(ArgumentError, "incomplete format specifier; use %% (double %) instead") do
       sprintf("abc%")
     end
   end