Signedness Checker emits false positive when a char is assigned to an int or long and returned

[DmitriyShepelev]

The Signedness Checker emits a false positive when a char is assigned to an int or a long and returned:

public class RemainingUnsignedness {
    int returnIntWithLocalVariable(char c) {
        int i = c;
        return i;
    }

    long returnLongWithLocalVariable(char c) {
        long l = c;
        return l;
    }

    int returnIntWithoutLocalVariable(char c) {
        return c;
    }

    long returnLongWithoutLocalVariable(char c) {
        return c;
    }
}

Output:

root@DESKTOP-MO4BCEL:~/checker-framework# javacheck -processor SignednessChecker ~/temp-checker/checker-framework/checker/tests/signedness/RemainingUnsignedness.java
/root/temp-checker/checker-framework/checker/tests/signedness/RemainingUnsignedness.java:4: error: [return.type.incompatible] incompatible types in return.
        return i;
               ^
  type of expression: @Unsigned int
  method return type: @Signed int
/root/temp-checker/checker-framework/checker/tests/signedness/RemainingUnsignedness.java:9: error: [return.type.incompatible] incompatible types in return.
        return l;
               ^
  type of expression: @Unsigned long
  method return type: @Signed long
2 errors

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

The methods returnIntWithoutLocalVariable and returnLongWithoutLocalVariable not emitting this false positive demonstrates the necessity of a local variable in emitting this false positive.