C++ compiler error when trying to use `self.position()` and another iterator

[bbannier]

I would have expected the following to work:

# foo.spicy
module foo;

public type X = unit {
    var start: iterator<stream>;
    on %init { self.start = self.input(); }

    : (Y(self.start))[];
};

type Y = unit(start: iterator<stream>) {
    y: uint8 { print self.position() - start; }
};

$ spicyc -j foo.spicy
  /private/var/folders/ht/vtb0rkbd4ws15vx02xdb84zw0000gn/T/foo_3938bf4a0abadc65-b1279778a4c61f1.cc:573:45: error: invalid
 operands to binary expression ('std::optional< ::hilti::rt::stream::SafeConstIterator>' and '::hilti::rt::stream::SafeCo
nstIterator')
      ::hilti::rt::print((*__self).__position - __self->__p_start, ::hilti::rt::Bool(true));
                         ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~
  /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/_
_ios/fpos.h:61:11: note: candidate template ignored: could not match 'fpos' against 'optional'
  streamoff operator-(const fpos<_StateT>& __x, const fpos<_StateT>& __y) {
            ^
  /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/_
_iterator/reverse_iterator.h:296:1: note: candidate template ignored: could not match 'reverse_iterator' against 'optiona
l'
  operator-(const reverse_iterator<_Iter1>& __x, const reverse_iterator<_Iter2>& __y)
  ^
  /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/_
_iterator/wrap_iter.h:245:6: note: candidate template ignored: could not match '__wrap_iter' against 'optional'
  auto operator-(const __wrap_iter<_Iter1>& __x, const __wrap_iter<_Iter2>& __y) _NOEXCEPT
       ^
  /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.3.sdk/usr/include/c++/v1/_
_iterator/move_iterator.h:283:6: note: candidate template ignored: could not match 'move_iterator' against 'optional'
  auto operator-(const move_iterator<_Iter1>& __x, const move_iterator<_Iter2>& __y)
       ^
  /Users/bbannier/src/spicy/hilti/runtime/include/hilti/rt/3rdparty/SafeInt/SafeInt.hpp:6731:30: note: candidate template
 ignored: could not match 'SafeInt<T, E>' against '::hilti::rt::stream::SafeConstIterator'
  _CONSTEXPR14 SafeInt< T, E > operator -( U lhs, SafeInt< T, E > rhs ) SAFEINT_CPP_THROW
                               ^
  1 error generated.
  [error] spicy-driver: JIT compilation failed

We should either do the expected for this code or reject it.

[bbannier]

This was fixed by #1439.