Kernel#sprintf must raise ArgumentError on dangling '%' chars in format string since Ruby 2.5

nomadium · nomadium · commit 49a74b95fbd7 · 2018-03-25T14:26:50.000+01:00
diff --git a/core/src/main/java/org/jruby/util/Sprintf.java b/core/src/main/java/org/jruby/util/Sprintf.java
@@ -90,6 +90,7 @@ public class Sprintf {
     private static final String ERR_MALFORMED_DOT_NUM = "malformed format string - %.[0-9]";
     private static final String ERR_MALFORMED_STAR_NUM = "malformed format string - %*[0-9]";
     private static final String ERR_ILLEGAL_FORMAT_CHAR = "illegal format character - %";
+    private static final String ERR_INCOMPLETE_FORMAT_SPEC = "incomplete format specifier; use %%%% (double %%) instead";
     private static final String ERR_MALFORMED_NAME = "malformed name - unmatched parenthesis";
 
     private static final ThreadLocal<Map<Locale, NumberFormat>> LOCALE_NUMBER_FORMATS = new ThreadLocal<Map<Locale, NumberFormat>>();
@@ -1413,6 +1414,7 @@ else if ((flags & FLAG_MINUS) != 0) {
             if (incomplete) {
                 if (flags == FLAG_NONE) {
                     // dangling '%' char
+                    if (format[length - 1] == '%') raiseArgumentError(args,ERR_INCOMPLETE_FORMAT_SPEC);
                     buf.append('%');
                 } else {
                     raiseArgumentError(args,ERR_ILLEGAL_FORMAT_CHAR);
