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, 4 insertions, 2 deletions

diff --git a/op.h b/op.h
index 0758f9c910..ffa9a3f163 100644
--- a/op.h
+++ b/op.h
@@ -225,7 +225,7 @@ Deprecated.  Use C<GIMME_V> instead.
 #define OPpEARLY_CV		32	/* foo() called before sub foo was parsed */
   /* OP_?ELEM only */
 #define OPpLVAL_DEFER		16	/* Defer creation of array/hash elem */
-  /* OP_RV2?V, OP_GVSV, OP_ENTERITER only */
+  /* OP_RV2[SAH]V, OP_GVSV, OP_ENTERITER only */
 #define OPpOUR_INTRO		16	/* Variable was in an our() */
   /* OP_RV2[AGH]V, OP_PAD[AH]V, OP_[AH]ELEM, OP_[AH]SLICE OP_AV2ARYLEN,
      OP_R?KEYS, OP_SUBSTR, OP_POS, OP_VEC */
@@ -242,6 +242,7 @@ Deprecated.  Use C<GIMME_V> instead.
 #define OPpDONT_INIT_GV		4	/* Call gv_fetchpv with GV_NOINIT */
 /* (Therefore will return whatever is currently in the symbol table, not
    guaranteed to be a PVGV)  */
+#define OPpALLOW_FAKE		16	/* OK to return fake glob */
 
 /* Private for OP_ENTERITER and OP_ITER */
 #define OPpITER_REVERSED	4	/* for (reverse ...) */
@@ -308,7 +309,8 @@ Deprecated.  Use C<GIMME_V> instead.
 #define OPpOFFBYONE		128	/* Treat caller(1) as caller(2) */
 
 /* Private for OP_COREARGS */
-/* These must not conflict with OPpDONT_INIT_GV.  See pp.c:S_rv2gv. */
+/* These must not conflict with OPpDONT_INIT_GV or OPpALLOW_FAKE.
+   See pp.c:S_rv2gv. */
 #define OPpCOREARGS_DEREF1	1	/* Arg 1 is a handle constructor */
 #define OPpCOREARGS_DEREF2	2	/* Arg 2 is a handle constructor */
 #define OPpCOREARGS_SCALARMOD	64	/* \$ rather than \[$@%*] */