while (1) {
    $i = 0;
  again:
    my $x;
    goto again if $i++ < 100_000_000;
}
[download]

Dave.

That depends on how you define "memory leak".

At least under Wikipedias definition ("In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations1 in such a way that memory which is no longer needed is not released.") this still is a leak. Because the main scope is never exited (while the program is running) there is at least one scope that never releases its memory.

And then there are closures. See the following code that also exhibits the memory leak:

#!/usr/bin/perl

my $i;

top:

while (1) {
  again:
    my $x;
    $i = 0;
    goto again if $i++ < 100_000;
}

goto top;
[download]

Necessarily the hook variable has to be in the main scope (I assume), but the interesting thing is that the code seems to be minimal for the closure case, i.e. $i creates the closure, but $x is needed to create the leak.

UPDATE:Anon Monk found a silly mistake in my code, the inner goto is an endless loop. The conclusion is wrong, I tested closures with teh following code and memory stayed low.

sub closure {
        my $s;
        return sub { $s=5; my $i; }
    }

    my $f = closure();

while (1) {
    $f->();
}
[download]

there is at least one scope that never releases its memory.

In your original program, yes. It never releases memory, but that memory is still needed. That doesn't meet the definition of a leak.

Keep in mind that the run-time effect of

my $i;
[download]

is similar to

Hook::Scope::POST(sub { $i = undef });
[download]

It pushes an instruction on the stack to clear the scope on exit (which could happen, say, if an exception occurs).

That snippet exhibits an infinite loop, or two. The goto is always taken since $i++ < 100_000 will always be true...

Objects may have side effects when they are DESTROYed, so this must happen at some well-defined moment (scope exit). Gotos cannot create scopes as there is no way to determine the flow of the program.