Bison C++ mid-rule value lost with variants

[Piotr Marcińczyk]

I supposedly found a bug in lalr1.cc skeleton with variant semantic type.
When using mid-rule action { $<type>$ = value; } to return a value that
will be used in further semantic actions, it appears that the value on
stack becomes zero. Tested with Bison version 3.0.4.

Link to a minimal working example:
https://pastebin.com/bwsTSWNU

Link to StackOverflow question about it:
https://stackoverflow.com/q/44811550/1538920

​Best regards,

Piotr Marcińczyk