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’.

1 files changed, 10 insertions, 1 deletions

diff --git a/t/io/tell.t b/t/io/tell.t
index 8e4f14e55d..5fe65b3a0f 100644
--- a/t/io/tell.t
+++ b/t/io/tell.t
@@ -6,7 +6,7 @@ BEGIN {
     require './test.pl';
 }
 
-print "1..28\n";
+print "1..31\n";
 
 $TST = 'TST';
 
@@ -160,3 +160,12 @@ if (tell($tst) == 6)
 { print "ok 28$todo\n"; } else { print "not ok 28$todo\n"; }
 close $tst;
 
+open FH, "test.pl";
+$fh = *FH; # coercible glob
+$not = "not " x! (tell $fh == 0);
+print "${not}ok 29 - tell on coercible glob\n";
+$not = "not " x! (tell == 0);
+print "${not}ok 30 - argless tell after tell \$coercible\n";
+tell *$fh;
+$not = "not " x! (tell == 0);
+print "${not}ok 31 - argless tell after tell *\$coercible\n";