In bison 3.2.3, given a parser definition that starts like this:
%require "3.0.2"
%defines
%define parser_class_name {RezParser}
%skeleton "lalr1.cc"
%locations;
%define api.token.constructor
%define api.value.type variant
%define parse.assert
%token<int> INTLIT;
//…
the following code crashes:
std::string filename = "foo";
yy::location loc(&filename, 0,0);
auto sym = RezParser::make_INTLIT(42, loc);
auto sym2 = std::move(sym);
Assertion failed: (yytypeid_), function as, file
/Users/wolfgang/Projects/Retro68-build/build-host/Rez/RezParser.generated.hh,
line 370.
The reason is that variant::destroy<int> gets called twice.
When basic_symbol<by_type>::move is used, variant::move is invoked, which
destroys the source, and by_type::move is invoked, which resets the source’s
type to empty.
When basic_symbol’s move constructor is used, variant::move is invoked as well,
but by_type’s constructor is used. Because by_type has no move constructor, it
never resets the source object’s type to empty, and so the variant will be
desrtroyed again when basic_symbol’s destructor is invoked.
Suggested fix: by_type needs a move constructor that acts like by_type::move.
I also suggest that the fact that yy:: parser_class_name::symbol_type is no
longer copy-constructible in bison 3.2 should be listed as a breaking change
from bison 3.0.
Cheers,
Wolfgang
