Flatten vstrings modified in place
A substitution forces its target to a string upon successful substitu-
tion, even if the substitution did nothing:
$ ./perl -Ilib -le '$a = *f; $a =~ s/f/f/; print ref \$a'
SCALAR
Notice that $a is no longer a glob after s///.
But vstrings are different:
$ ./perl -Ilib -le '$a = v102; $a =~ s/f/f/; print ref \$a'
VSTRING
I fixed this in 5.16 (
1e6bda93) for those cases where the vstring ends
up with a value that doesn’t correspond to the actual string:
$ ./perl -Ilib -le '$a = v102; $a =~ s/f/o/; print ref \$a'
SCALAR
It works through vstring set-magic, that does the check and removes
the magic if it doesn’t match.
I did it that way because I couldn’t think of any other way to fix
bug #29070, and I didn’t realise at the time that I hadn’t fixed
all the bugs.
By making SvTHINKFIRST true on a vstring, we force it through
sv_force_normal before any in-place string operations. We can also
make sv_force_normal handle vstrings as well. This fixes all the lin-
gering-vstring-magic bugs in just two lines, making the vstring set-
magic (which is also slow) redundant. It also allows the special case
in sv_setsv_flags to be removed.
Or at least that was what I had hoped.
It turns out that pp_subst, twists and turns in tortuous ways, and
needs special treatment for things like this.
And do_trans functions wasn’t checking SvTHINKFIRST when arguably it
should have.
I tweaked sv_2pv{utf8,byte} to avoid copying magic variables that do
not need copying.