Should -2147483648 be accepted or not?
In Java, -2147483648 (INT_MIN) is a valid int literal. However, MiniJava only has positive integer literals, which would make this a unary expression -(2147483648) and thus invalid, since 2147483648 = INT_MAX + 1. On the other hand, it would be trivial to deal with this during the parsing stage (or even during constant folding).
(Note that even without accepting -2147483648, it is possible to obtain that value in Minijava by writing (-2147483647 - 1))