False positives for unused variable

[nordlow]

The current diagnostics of unused variables is incomplete and gives false positives because it doesn't take into account the possibility of values passed to a ref-parameter of a function f can being mutated inside the f. For instance

void inc(T)(ref T x) {
    x =+ 1;
}

@safe pure unittest {
    int x = 1;
    inc(x);
    assert(x == 2);
}

gives warning

Variable x is never modified and could have been declared const or immutable.

but shouldn't.