use experimental :pack is ignored even if it is surely called

[titsuki]

The Problem

See:
https://travis-ci.org/titsuki/p6-MeCab/jobs/406780390
https://github.com/titsuki/p6-MeCab/blob/0.0.6/lib/MeCab/Lattice.pm6#L3
https://github.com/titsuki/p6-MeCab/blob/0.0.6/lib/MeCab/Lattice.pm6#L169

Even if I surely call use experimental :pack, it still warns to use use experimental :pack and abends when I call unpack.

Expected Behavior

It doesn't cause any warns.

Actual Behavior

It causes an error and abends.

Steps to Reproduce

See:
https://github.com/titsuki/p6-MeCab/blob/0.0.6/t/02-lattice.t

All of the methods that calls multi method feature-constraint(Int $begin-pos, Int $end-pos, Str $feature) can cause errors.

Environment

• Operating system: Ubuntu 14.04.5 LTS
• Compiler version (perl6 -v): Rakudo version 2018.06-234-gcb2ea9328 built on MoarVM version 2018.06-304-g4d22fb9e7

[lizmat]

This is probably a complication of the new frame walker logic that Jonathan implemented in Moar.

I have no current solution, but a possible workaround: could you try moving the use experimental :pack to the method in which you use the .unpack ? This would probably, longer term, also be more efficient as it would have to walk fewer frames to find out if it is ok to use .unpack.

There is also a P5pack module in the ecosystem that you might want to have a look at.

[titsuki]

@lizmat thanks for your advice! I'll try it later.