From a333aabbd8178d79e5fb3838e7e22e4de3c7127f Mon Sep 17 00:00:00 2001
From: James E Keenan <jkeenan@cpan.org>
Date: Thu, 10 Oct 2019 18:49:20 -0400
Subject: [PATCH] Do not use 'exists' on arrays; use 'defined' instead

pod/perlfunc.pod advises us:

       WARNING: Calling "exists" on array values is strongly
       discouraged. The notion of deleting or checking the existence of
       Perl array elements is not conceptually coherent, and can lead
       to surprising behavior.

While trying to extend the test coverage of Dumpvalue.pm, two instances
of 'exists ARRAYREF' were noted.  In the second of these two instances,
using 'exists ARRAYREF' resulted in the 'if' condition of an if/else
block always returning true, thereby making the corresponding 'else'
condition unreachable -- a situation which was confirmed by coverage
analysis.

We should only use best practices in modules maintained by Perl 5
Porters; this patch implements that.  When we do so, a different (but
actually better) error message appears in the second instance; so tests
are updated as well.
---
 dist/Dumpvalue/lib/Dumpvalue.pm        | 6 +++---
 dist/Dumpvalue/t/rt-134441-dumpvalue.t | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/dist/Dumpvalue/lib/Dumpvalue.pm b/dist/Dumpvalue/lib/Dumpvalue.pm
index 3faf829538..cc14cc4701 100644
--- a/dist/Dumpvalue/lib/Dumpvalue.pm
+++ b/dist/Dumpvalue/lib/Dumpvalue.pm
@@ -1,7 +1,7 @@
 use 5.006_001;			# for (defined ref) and $#$v and our
 package Dumpvalue;
 use strict;
-our $VERSION = '1.19';
+our $VERSION = '1.21';
 our(%address, $stab, @stab, %stab, %subs);
 
 sub ASCII { return ord('A') == 65; }
@@ -254,7 +254,7 @@ sub unwrap {
       if ($#$v >= 0) {
 	$short = $sp . "0..$#{$v}  " .
 	  join(" ", 
-	       map {exists $v->[$_] ? $self->stringify($v->[$_]) : "empty"} (0..$tArrayDepth)
+	       map {defined $v->[$_] ? $self->stringify($v->[$_]) : "empty"} (0..$tArrayDepth)
 	      ) . "$shortmore";
       } else {
 	$short = $sp . "empty array";
@@ -264,7 +264,7 @@ sub unwrap {
     for my $num (0 .. $tArrayDepth) {
       return if $DB::signal and $self->{stopDbSignal};
       print "$sp$num  ";
-      if (exists $v->[$num]) {
+      if (defined $v->[$num]) {
         $self->DumpElem($v->[$num], $s);
       } else {
 	print "empty slot\n";
diff --git a/dist/Dumpvalue/t/rt-134441-dumpvalue.t b/dist/Dumpvalue/t/rt-134441-dumpvalue.t
index cc9f270f5a..324845d48d 100644
--- a/dist/Dumpvalue/t/rt-134441-dumpvalue.t
+++ b/dist/Dumpvalue/t/rt-134441-dumpvalue.t
@@ -39,11 +39,11 @@ is( $y, $x,
 @foobar = (undef, 'bar');
 $d->dumpValue([@foobar]);
 $x = $out->read;
-is( $x, "0  undef\n1  'bar'\n",
+is( $x, "0  empty slot\n1  'bar'\n",
     'dumpValue worked on array ref, first element undefined' );
 $d->dumpValues(@foobar);
 $y = $out->read;
-is( $y, "0  undef\n1  'bar'\n",
+is( $y, "0  empty slot\n1  'bar'\n",
     'dumpValues worked on array, first element undefined' );
 is( $y, $x,
     "dumpValues called on array returns same as dumpValue on array ref, first element undefined");
@@ -51,11 +51,11 @@ is( $y, $x,
 @foobar = ('bar', undef);
 $d->dumpValue([@foobar]);
 $x = $out->read;
-is( $x, "0  'bar'\n1  undef\n",
+is( $x, "0  'bar'\n1  empty slot\n",
     'dumpValue worked on array ref, last element undefined' );
 $d->dumpValues(@foobar);
 $y = $out->read;
-is( $y, "0  'bar'\n1  undef\n",
+is( $y, "0  'bar'\n1  empty slot\n",
     'dumpValues worked on array, last element undefined' );
 is( $y, $x,
     "dumpValues called on array returns same as dumpValue on array ref, last element undefined");
-- 
2.17.1