Hints hash should not store references

[atoomic]

This was discussed already on RT:

• https://rt.cpan.org/Ticket/Display.html?id=128044
• https://rt.cpan.org/Ticket/Display.html?id=128053

But I think it worth giving this some visibility there. It's a bad idea to store references in the Hash Hint a.k.a. %^H

A quick grep show that both the .pm and .xs code need some fixup

Changes:32:          - rewrite pragma implementation and the way %^H is used
Parameters.xs:2172:            croak("%s: internal error: $^H{'%s'} not a hashref: %"SVf, MY_PKG, HINTK_CONFIG, SVfARG(sv));
Parameters.xs:2182:            croak("%s: internal error: $^H{'%s'}{'%.*s'} not a hashref: %"SVf, MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, SVfARG(sv));
Parameters.xs:2205:        croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'} not set", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_ ## NAME); \
Parameters.xs:2218:            croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'} not a coderef: %"SVf, MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_REIFY, SVfARG(sv));
Parameters.xs:2234:                    croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: expected '$', found '%.*s'", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (int)(sv_p_end - p), p);
Parameters.xs:2238:                    croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: expected idfirst, found '%.*s'", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (int)(sv_p_end - p), p);
Parameters.xs:2246:                    croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: can't use global $_ as a parameter", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT);
Parameters.xs:2252:                            croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: %"SVf" can't appear twice", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, SVfARG((*ppspec)->shift.data[i].name));
Parameters.xs:2269:                            croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'} not an arrayref: %"SVf, MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIF2, SVfARG(sv));
Parameters.xs:2274:                        croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: tix [%ld] out of range [%ld]", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (long)tix, (long)(av_len(shift_types) + 1));
Parameters.xs:2278:                        croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: tix [%ld] doesn't exist", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (long)tix);
Parameters.xs:2282:                        croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: tix [%ld] is not an object (%"SVf")", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (long)tix, SVfARG(type));
Parameters.xs:2289:                        croak("%s: internal error: $^H{'%s'}{'%.*s'}{'%s'}: expected ' ', found '%.*s'", MY_PKG, HINTK_CONFIG, (int)kw_len, kw_ptr, HINTSK_SHIFT, (int)(sv_p_end - p), p);
lib/Function/Parameters.pm:351:    my %config = %{$^H{+HINTK_CONFIG} // {}};
lib/Function/Parameters.pm:378:    $^H{+HINTK_CONFIG} = \%config;
lib/Function/Parameters.pm:385:        delete $^H{+HINTK_CONFIG};
lib/Function/Parameters.pm:389:    my %config = %{$^H{+HINTK_CONFIG}};
lib/Function/Parameters.pm:391:    $^H{+HINTK_CONFIG} = \%config;

It appears that this is the only CPAN module to store HINTK_CONFIG there so this should be safe, to move it to a better location.

https://grep.metacpan.org/search?size=20&q=HINTK_CONFIG&qd=&qft=

Maybe a GV in Function::Parameters itself?