optional<bytes> differs between struct and tuple only as a parameter

[ynadji]

This came up when trying to convert a struct to a tuple in Spicy to pass to Zeek. This same construct worked with uint64 but failed with a cryptic error when I tried the same thing with bytes. It's possible other types would meet the same fate. Code and error follow:

module Foo;

type Bar = struct {
  wutang: bytes &optional;
};

type BarTuple = tuple<
  wutang: optional<bytes>
>;

public function make_bar_tuple(bar: Bar): BarTuple {
  local nope: optional<bytes>;
  return (
    bar?.wutang ? optional(bar.wutang) : nope
  );
}

¡ spicy-build -o foo foo.spicy
[error] foo.spicy:14:5: types of alternatives do not match in ternary expression (optional<bytes> vs. optional<bytes>)
[error] spicyc: aborting after errors

However, if bar is instead declared locally, it compiles without issue:

module Foo;

type Bar = struct {
  wutang: bytes &optional;
};

type BarTuple = tuple<
  wutang: optional<bytes>
>;

public function make_bar_tuple(): BarTuple {
  local bar: Bar;
  local nope: optional<bytes>;
  return tuple(bar?.wutang ? optional(bar.wutang) : nope);
}

(Fixed code to actually return tuple instead instead of optional - Robin).

[bbannier]

The issue here is that while type comparison initially invokes sameExceptForConstness two different type nodes without typeID or cxxID were created so we forward to the node equality check Type::isEqual https://github.com/zeek/spicy/blob/d525ad3038724e8543a8387372bb29e21c4461f6/hilti/toolchain/include/ast/type.h#L368= which ultimately calls operator==(const Type&, const Type&) (which takes constness into account). The proper fix is probably to also add support for sameExceptForConstness on the node level.

[bbannier]

It looks like no quick fix is possible here. Instead of pushing sameExceptForConstness the proper fix is probably to instead move constness out of the type information, and then handle it explicitly where needed.

Unassigning myself for now.

[rsmmr]

(deleted my previous comment as it wasn't right.)