Devel-PPPort: add SvVSTRING()

vstrings were originally added in perl-5.8.0-82-g92f0c26562,
SvVSTRING_mg() was originally added in perl-5.8.0-8018-gb0a11fe104 so
technically in the same release.

I expect there were some uses of intermediate versions 19 years ago,
but I don't think we need to worry about it now.

Author: tonycoz

dist/Devel-PPPort/parts/embed.fnc

@@ -1960,6 +1960,9 @@ Apd	|void	|sv_vcatpvfn_flags|NN SV *const sv|NN const char *const pat|const STRL
 Apd	|void	|sv_vsetpvfn	|NN SV *const sv|NN const char *const pat|const STRLEN patlen \
 				|NULLOK va_list *const args|NULLOK SV **const svargs \
 				|const Size_t sv_count|NULLOK bool *const maybe_tainted
+Adp	|const char *|sv_vstring_get					\
+				|NN SV * const sv			\
+				|NULLOK STRLEN *lenp
 CpR	|NV	|str_to_version	|NN SV *sv
 Ap	|void	|regdump	|NN const regexp* r
 CiTop	|struct regexp *|ReANY	|NN const REGEXP * const re

dist/Devel-PPPort/parts/inc/magic

@@ -23,6 +23,9 @@ SvUV_nomg
 SvNV_nomg
 SvTRUE_nomg
 
+sv_vstring_get
+SvVSTRING
+
 =implementation
 
 #undef  SvGETMAGIC
@@ -254,10 +257,36 @@ sv_unmagicext(pTHX_ SV *const sv, const int type, const MGVTBL *vtbl)
 #endif
 #endif
 
+__UNDEFINED__ SvVSTRING(sv, len)  (sv_vstring_get(sv, &(len)))
+__UNDEFINED__ SvVOK(sv) (FALSE)
+
+#if !defined(sv_vstring_get)
+
+#if { NEED sv_vstring_get }
+
+const char *
+sv_vstring_get(pTHX_ SV *sv, STRLEN *lenp)
+{
+#ifdef SvVSTRING_mg
+    MAGIC *mg = SvVSTRING_mg(sv);
+    if (!mg) return NULL;
+
+    if (lenp) *lenp = mg->mg_len;
+    return mg->mg_ptr;
+#else
+    return NULL;
+#endif
+}
+
+#endif
+
+#endif
+
 =xsinit
 
 #define NEED_mg_findext
 #define NEED_sv_unmagicext
+#define NEED_sv_vstring_get
 
 #ifndef STATIC
 #define STATIC static
@@ -580,7 +609,26 @@ magic_SvPV_nomg_nolen(sv)
 
 #endif
 
-=tests plan => 63
+int
+SvVOK(sv)
+    SV *sv
+
+SV *
+SvVSTRING(sv)
+    SV *sv
+    CODE:
+    {
+        const char *vstr_pv;
+        STRLEN vstr_len;
+        if((vstr_pv = SvVSTRING(sv, vstr_len)))
+            RETVAL = newSVpvn(vstr_pv, vstr_len);
+        else
+            RETVAL = &PL_sv_undef;
+    }
+    OUTPUT:
+        RETVAL
+
+=tests plan => 64
 
 # Find proper magic
 ok(my $obj1 = Devel::PPPort->new_with_mg());
@@ -725,6 +773,18 @@ if (ivers($]) >= ivers("5.6")) {
 is tied($big)->{fetch}, 1;
 is tied($big)->{store}, 0;
 
+SKIP:
+{
+    my $vstr = eval "v1.23.456";
+
+    if (!Devel::PPPort::SvVOK($vstr)) {
+        skip "No vstring magic", 1;
+        last SKIP; # testutil skip() doesn't "last SKIP"
+    }
+
+    is Devel::PPPort::SvVSTRING($vstr), "v1.23.456", 'SvVSTRING()';
+}
+
 package TieScalarCounter;
 
 sub TIESCALAR {