for my ($x) ...: fix handling of degenerate 1-var

The new

    for my ($x,$y,...) (...) { ... }

syntax has a couple of problems in the degenerate case of a single
variable:

    for my ($x) (...) { ... }

First, the loop variable is marked as lexical, but not as a variable
to be introduced. So it behaves roughly as if written like:

    { my $x; for $x (...) { ... } }

I can't think of any user-visible runtime change in behaviour this bug
causes, so I haven't included a test for it.

Second, it was being incorrectly deparsed as

    for $x (...) { ... }

(i.e. without the 'my').

This commit fixes both of these issues.

The basic problem is that the parser, in the case of multiple vars,
passes a list subtree of PADSVs as the 'sv' argument of Perl_newFOROP,
but in the case of a single var, passes a single PADSV op instead.
This single PADSV doesn't have the LVINTRO flag set, so is
indistinguishable from plain

    my $x; for $x ....

This commit makes the parser set the OPf_PARENS flag on the lone PADSV
to signal to newFOROP() that it's a degenerate 1-var list, and
newFOROP() sets the OPf_PARENS flag on the ENTERITER op to signal to the
deparser that this is "for my (...)" syntax, even if it only has a
single var.

1 files changed, 6 insertions, 3 deletions

diff --git a/lib/B/Deparse.pm b/lib/B/Deparse.pm
index b50608ca86..bdf3b3961f 100644
--- a/lib/B/Deparse.pm
+++ b/lib/B/Deparse.pm
@@ -3978,10 +3978,13 @@ sub loop_common {
 	} else {
 	    $ary = $self->deparse($ary, 1);
 	}
-        my $iter_targ = $kid->first->first->targ;
-        if ($iter_targ) {
+
+        if ($enter->flags & OPf_PARENS) {
+            # for my ($x, $y, ...) ...
             # for my ($foo, $bar) () stores the count (less 1) in the targ of
-            # the ITER op.
+            # the ITER op. For the degenerate case of 1 var ($x), the
+            # TARG is zero, so it works anyway
+            my $iter_targ = $kid->first->first->targ;
             my @vars;
             my $targ = $enter->targ;
             while ($iter_targ-- >= 0) {