Missing typechecking rules for augmented assignments

[byakuren-hijiri]

Augmented assignments could be used with the following operations: "+" | "-" | "*" | "/" | "%".

It seems reasonable that these operations should be applied to numeric types, but this is not always the case.

Consider their behavior on different types:

1. Bool

   get fun test_bool(): Bool {
       let a: Bool = false;
       a %= true;
       return a;
   }

Generates the following FunC code:

(tuple, int) $SampleTactContract$_fun_test_bool(tuple $self) impure inline_ref {
    var ($self) = $self;
    int $a = false;
    $a = $a % true;
    return ($self, $a);
}

It seems correct from the func perspective, so it passes the compilation. But the question is what the user is expected to get?

2. String and Address

   get fun test_string(): String {
       let a: String = "foo";
       a %= "bar";
       return a;
   }

The func compilation fails:

💼 Compiling project sample...
   > SampleTactContract: tact compiler
   > SampleTactContract: func compiler
Func compilation error: output/sample_SampleTactContract.code.fc:30:20: error: cannot apply function _%_ : (int, int) -> int to arguments of type (slice, slice): cannot unify type slice with int
      $a1 = $a1 % $a2;
💥 Compilation failed. Skipping packaging

3. More complex types The FunC compilation fails, as we are trying to apply an arithmetic operation to a non-numeric type.

---

Therefore, it is suggested to restrict these augmented assignment operations for all non-numeric types. If we are going to add boolean operations later, we should consider this in the typechecking as well.