FULL PRODUCT VERSION :
java version "1.8.0_112"
Java(TM) SE Runtime Environment (build 1.8.0_112-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.112-b15, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [version 10.0.14393]

A DESCRIPTION OF THE PROBLEM :
Pattern.compile throws StringIndexOutOfBoundsException instead of PatternSyntaxException for the pattern string "[" with canonical equivalence (CANON_EQ) flag set.

See https://josm.openstreetmap.de/ticket/13870 for a real-life scenario where a pattern is validated during user input.

As per QUality outreach, please add "josm-found" label to this bug report.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run the following code:

Pattern.compile("[", Pattern.CANON_EQ);

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
PatternSyntaxException
ACTUAL -
StringIndexOutOfBoundsException

ERROR MESSAGES/STACK TRACES THAT OCCUR :
java.lang.StringIndexOutOfBoundsException: String index out of range: 1
at java.lang.String.codePointAt(String.java:687)
at java.util.regex.Pattern.normalizeCharClass(Pattern.java:1416)
at java.util.regex.Pattern.normalize(Pattern.java:1392)
at java.util.regex.Pattern.compile(Pattern.java:1659)
at java.util.regex.Pattern.<init>(Pattern.java:1351)
at java.util.regex.Pattern.compile(Pattern.java:1054)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.regex.Pattern;

public class PatternBug {
    public static void main(String[] args) throws Exception {
        Pattern.compile("[", Pattern.CANON_EQ);
   }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
catch StringIndexOutOfBoundsException in caller's code