Coditional method invocation may have an incorrect side effect

[ggleyzer]

The code to reproduce the bug:

module Reproducer {
    void run() {
        Char[] chars = new Array<Char>(2);
        Int offset = 0;
        if (chars[offset++] := next()) {
            assert offset == 1;
        } else {
            // the offset must not have been incremented, but it has been
            assert offset == 0;
        }
    }

    conditional Char next() = False;
}

Currently, the offset++ increment happens before the conditional method next() is called, which is wrong. It should only happen after next{} returns with a positive (True) result.

Similarly, the following code works incorrectly; the index() method must not be called upon a negative response from next() method.

module Reproducer2 {
    void run() {
        Char[] chars = new Array<Char>(2);
        chars[index()] := next();
    }

    conditional Char next() = False;

    Int index() {
        assert False as "This should not be called";
    }
}