Stop tell($glob_copy) from clearing PL_last_in_gv
This bug is a side effect of rv2gv’s starting to return an incoercible
mortal copy of a coercible glob in 5.14:
$ perl5.12.4 -le 'open FH, "t/test.pl"; $fh=*FH; tell $fh; print tell'
0
$ perl5.14.0 -le 'open FH, "t/test.pl"; $fh=*FH; tell $fh; print tell'
-1
In the first case, tell without arguments is returning the position of
the filehandle.
In the second case, tell with an explicit argument that happens to
be a coercible glob (tell has an implicit rv2gv, so tell $fh is actu-
ally tell *$fh) sets PL_last_in_gv to a mortal copy thereof, which is
freed at the end of the statement, setting PL_last_in_gv to null. So
there is no ‘last used’ handle by the time we get to the tell without
arguments.
This commit adds a new rv2gv flag that tells it not to copy the glob.
By doing it unconditionally on the kidop, this allows tell(*$fh) to
work the same way.
Let’s hope nobody does tell(*{*$fh}), which will unset PL_last_in_gv
because the inner * returns a mortal copy.
This whole area is really icky. PL_last_in_gv should be refcounted,
but that would cause handles to leak out of scope, breaking programs
that rely on the auto-closing ‘feature’.