Re: [RFC perlmod] ffi glue: type detection: check actual SV flags instead of structural body type

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Tue, 10 Mar 2026 21:45:43 +0100, Thomas Lamprecht <t.lamprecht@proxmox.com> wrote:
> RSPL_type_flags and the RSPL_has_* helpers used a lookup table indexed
> by SvTYPE, which reflects the structural body layout (what slots are
> allocated) rather than which slots hold valid data. Since SV body types
> only upgrade and never downgrade, this caused misclassification [0].
> 
> For example, a string "65004" coerced to integer via int() still
> reported STRING|INTEGER|DOUBLE because SvTYPE remained SVt_PVNV. The
> deserializer then treated it as a string, and the SvPVutf8 call to
> read it set SVf_POK as a side effect, making the contamination
> permanent.
> 
> Replace the table with actual per-slot validity checks using
> SvIOKp/SvNOKp/SvPOKp. The private "p" variants are needed because
> SvOK (used in RSPL_is_defined) also considers private flags -- using
> only the public variants can leave defined values with no type flags.

Doing
    my $x = 3;
shows via Devel::Peek's Dump($x):
    FLAGS = (IOK,pIOK)

and after doing
    "stringify${x}"
or
    $x ~= /./

it shows
    FLAGS = (IOK,pIOK,pPOK)

indicating that *privately* it also has a string representation.

So IMO we could check public flags first, but then fall back to the old
code if they are empty for some reason?

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