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, 4 insertions, 0 deletions

diff --git a/perly.y b/perly.y
index 60eca783e1..55321fa41e 100644
--- a/perly.y
+++ b/perly.y
@@ -433,6 +433,10 @@ barestmt:	PLUGSTMT
 			}
 	|	FOR MY remember PERLY_PAREN_OPEN my_list_of_scalars PERLY_PAREN_CLOSE PERLY_PAREN_OPEN mexpr PERLY_PAREN_CLOSE mblock cont
 			{
+                          if ($my_list_of_scalars->op_type == OP_PADSV)
+                            /* degenerate case of 1 var: for my ($x) ....
+                               Flag it so it can be special-cased in newFOROP */
+                                $my_list_of_scalars->op_flags |= OPf_PARENS;
 			  $$ = block_end($remember, newFOROP(0, $my_list_of_scalars, $mexpr, $mblock, $cont));
 			  parser->copline = (line_t)$FOR;
 			}