Signedness Checker emits false positive error with casted unsigned right shift expression

[DmitriyShepelev]

The Signedness Checker emits a false positive error when the left operand of a casted (without an explicit signedness annotation) unsigned right shift expression is either a method parameter or field:

import org.checkerframework.checker.signedness.qual.Unsigned;
import org.checkerframework.checker.signedness.qual.Signed;

public class UnsignedRightShiftTestShort {
    void unsignedRightShiftWithParameter(int length) {
        byte b1 = (byte) (length >>> 24);
        byte b2 = (@Unsigned byte) (length >>> 24);
        byte b3 = (@Signed byte) (length >>> 24);
    }
}

Command: javacheck -version -verbose -AprintAllQualifiers -processor SignednessChecker UnsignedRightShiftTestShort.java

Output:
UnsignedRightShiftTestShortOutput.txt

javacheck alias:
alias javacheck='$CHECKERFRAMEWORK/checker/bin/javac'

In particular, the line byte b1 = (byte) (length >>> 24); emits the false positive error. This line should be legal, according to section 18.2.2 Permitted Shifts in the user manual.