result code = -1
standard error = {
tests/diagnostics/methods/mutating-method-on-rvalue.slang(13): error 30050: mutating method 'increment' cannot be called on an immutable value
        increment();
                 ^
tests/diagnostics/methods/mutating-method-on-rvalue.slang(13): note 30049: a 'this' parameter is an immutable parameter by default in Slang; apply the `[mutating]` attribute to the function declaration to opt in to a mutable `this`
tests/diagnostics/methods/mutating-method-on-rvalue.slang(25): error 30050: mutating method 'increment' cannot be called on an immutable value
    gCounter.increment();
                      ^
}
standard output = {
}