perl5db.pl: handling of undefined watch_expressions in _DB__handle_watch_expressions()

[hexcoder-]

(This is just an observation, not necessarily a bug.)

perl5db.pl as of commit c60ffc1

Module: perl5db.pl

Description

Reviewing the code for _DB__handle_watch_expressions()

perl5/lib/perl5db.pl

Line 2483 in 8cacb84

sub _DB__handle_watch_expressions

I found that using join here

perl5/lib/perl5db.pl

Line 2494 in 8cacb84

my ($val) = join( "', '", DB::eval(@_) );

makes $val always defined, since join always returns a (possibly empty) defined string.

Then in the following line

perl5/lib/perl5db.pl

Line 2495 in 8cacb84

$val = ( ( defined $val ) ? "'$val'" : 'undef' );

the false branch is never applied.

So maybe watchpoint expressions with result "undefined" are not reported correctly.

======================
My main motivation for looking here, was the behavior of watchpoints with regard to package scope changes.

In my application I had
my %hash;
along with some imported modules.

When my hash was populated completely (and should be constant afterwards), I wanted to see where and when $hash{'myEntry'} changed unexpectedly. But using a watchpoint w $hash{'myEntry'} in the debugger led to a lot of unwanted breaks: each time the package/module scope changed the visibility of %hash changed also, of course.

How these visibility changes can be ignored in watchpoint breaks, I do not not know yet (should this be another bug report?).

[tonycoz]

The visibility thing sound like a separate problem.

So maybe watchpoint expressions with result "undefined" are not reported correctly.

That looks like a regression introduced with the debugger refactor around 2012.

This changed the code from:

	my ($val) = &eval;	# Fix context (&eval is doing array)?
	$val = ( (defined $val) ? "'$val'" : 'undef' );

to what it is now:

            my ($val) = join( "', '", DB::eval(@_) );
            $val = ( ( defined $val ) ? "'$val'" : 'undef' );

I expect the fix is something like:

            my $val = join( ", ", map { defined ? "'$_'" : "undef" } DB::eval(@_) );