toExprOfTuple method with precise types

[anatoliykmetyuk]

Blocked by #7046.

[anatoliykmetyuk]

Rebased on master

[anatoliykmetyuk]

@nicolasstucki I have implemented some extra safety for this one.

  val tpl2: (Expr[1], 2, Expr[3]) = ('{1}, 2, '{3})
  '{val res = ${tpl2.toExprOfTuple}; res}  // error

In the previous implementation, this would have resulted in a class cast exception when doing asInstanceOf[Seq[Expr[_]] on the sequence representation of the tuple. In this implementation, we use an implicit predicate to verify that the tuple's type is correct. Furthermore, the implicit predicate also verifies the correctness of the match type InverseMap: the predicate assembles the result type in a logic programming style and then requires it to be equal to InverseMap which is visible to the end-user.

Hence, here we achieve safety without corrupting the end user's API. I believe this is a better way to go than having an Error["message"] type which forces the compiler to have an error: the input type, not the result type, is the one to be constrained.

I believe this pattern of having a companion predicate for match types can be a good safeguard when the match type is meant to be a partial type lambda, not a total one, and we need to verify the input type.

This still feels rather cumbersome though... Maybe we can find something more idiomatic.

Thanks @OlivierBlanvillain for helping with the solution.

[anatoliykmetyuk]

Rebased

[nicolasstucki]

The CI did not run for some reason