False positive when comparing two char with the Signedness checker

[txiang61]

Signedness checker complains about comparison between two char.

private static boolean isWhitespace(char c) {
    return c <= '\u0020';
}

Gives the following error:

error: [comparison.unsignedlhs] comparison has an unsigned LHS
    return c <= '\u0020';
           ^

From JLS https://docs.oracle.com/javase/specs/jls/se9/html/jls-5.html#jls-5.1.2

A widening conversion of a char to an integral type T zero-extends the representation of the char value to fill the wider format.

Comparison between two char should be safe.

[mernst]

I agree that the code you gave should pass type-checking. It seems to do so; see pull request #5167.

What version of the Checker Framework are you using?

[txiang61]

Thanks good to know it's already fixed. I'm on a very old version. Will update.