Alternative parser inside permutation parser synthesizes uninitialized optional<>

[edaskel@…]

In the process of developing a grammar I discovered a strange behavior where combining alternative and permutation parsers with attributeless parsers can result in invalid optional<> objects. For example, using "eps" as an example of an attributeless parser:

((int_ | eps) ^ eps)

is compatible with optional<int> and compiles successfully, but if you parse an input where the int is not present, an uninitialized optional<> is produced - it acts as though it stored an int, but the value is uninitialized (32766, 32765, or 32764, on my system).

The expression:

(-int_ ^ eps)

also displays this behavior.

I do have a workaround - using only the permutation parser works correctly.

[edaskel@…]

reduced testcase

[Nikita Kniazev <nok.raven@…>]

Fixed in ​https://github.com/boostorg/spirit/pull/319