Raise ArgumentError if sprintf format string ends with %

* Add tests and specs. See ruby/spec#401.
  Patch by Yuta Iwama and Shintaro Morikawa.
  [ruby-core:80153] [Bug #13315] [Fix GH-1560]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58890 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 12 insertions, 3 deletions

diff --git a/spec/rubyspec/core/string/modulo_spec.rb b/spec/rubyspec/core/string/modulo_spec.rb
index 249b15bf1e..4f26ac5033 100644
--- a/spec/rubyspec/core/string/modulo_spec.rb
+++ b/spec/rubyspec/core/string/modulo_spec.rb
@@ -14,9 +14,18 @@ describe "String#%" do
     ("%d%% %s" % [10, "of chickens!"]).should == "10% of chickens!"
   end
 
-  it "formats single % character at the end as literal %" do
-    ("%" % []).should == "%"
-    ("foo%" % []).should == "foo%"
+  ruby_version_is ""..."2.5" do
+    it "formats single % character at the end as literal %" do
+      ("%" % []).should == "%"
+      ("foo%" % []).should == "foo%"
+    end
+  end
+
+  ruby_version_is "2.5" do
+    it "raises an error if single % appears at the end" do
+      lambda { ("%" % []) }.should raise_error(ArgumentError)
+      lambda { ("foo%" % [])}.should raise_error(ArgumentError)
+    end
   end
 
   it "formats single % character before a newline as literal %" do