lib/dumpvar.pl: replace 'while .. each' with 'for'

This eliminates the warning reported in GH #23663 when you use 'X' or 'V
main' in the Perl debugger.

Add tests for 'X' and 'V main' to demonstrate that when loading they no
longer warn about undefined behavior.  Update MANIFEST.

Fixes: GH #23663.

Author: jkeenan

MANIFEST

@@ -5451,6 +5451,7 @@ lib/perl5db/t/gh-17660					Tests for the Perl debugger
 lib/perl5db/t/gh-17661					Tests for the Perl debugger
 lib/perl5db/t/gh-17661b					Tests for the Perl debugger
 lib/perl5db/t/gh-21350					Tests for the Perl debugger
+lib/perl5db/t/gh-23663					Tests for the Perl debugger
 lib/perl5db/t/load-modules				Tests for the Perl debugger
 lib/perl5db/t/lsub-n					Test script used by perl5db.t
 lib/perl5db/t/lvalue-bug				Tests for the Perl debugger

lib/dumpvar.pl

@@ -482,7 +482,8 @@ sub main::dumpvar {
     local $TotalStrings = 0;
     local $Strings = 0;
     local $CompleteTotal = 0;
-    while (($key,$val) = each(%stab)) {
+    for my $key (keys %stab) {
+        my $val = $stab{$key};
         return if $DB::signal;
         next if @vars && !grep( matchvar($key, $_), @vars );
         if ($usageOnly) {

lib/perl5db.t

@@ -3662,6 +3662,46 @@ EOS
     $wrapper->contents_like(qr/print "2\\n"/, "break immediately after defining problem");
 }
 
+{
+    # gh #23663 (variant 1)
+    my $wrapper = DebugWrap->new(
+        {
+            cmds =>
+            [
+                'b 4',
+                'X',
+                'c',
+                'q',
+            ],
+            prog => '../lib/perl5db/t/gh-23663',
+        }
+    );
+
+    $wrapper->contents_unlike(
+        qr/Use of each\(\) on hash after insertion without resetting hash iterator results in undefined behavior/,
+        q/gh-23663: 'X' command does not warn about undefined behavior/,
+       );
+
+    # gh #23663 (variant 2)
+    $wrapper = DebugWrap->new(
+        {
+            cmds =>
+            [
+                'b 4',
+                'v main',
+                'c',
+                'q',
+            ],
+            prog => '../lib/perl5db/t/gh-23663',
+        }
+    );
+
+    $wrapper->contents_unlike(
+        qr/Use of each\(\) on hash after insertion without resetting hash iterator results in undefined behavior/,
+        q/gh-23663: 'V main' command does not warn about undefined behavior/,
+       );
+}
+
 done_testing();
 
 END {

lib/perl5db/t/gh-23663

@@ -0,0 +1,4 @@
+# Issue:        https://github.com/Perl/perl5/issues/23663
+# Pull Request: https://github.com/Perl/perl5/issues/23669
+
+my $foo = "bar";