included from a line 2:
included from b line 5:
error in err:
Bareword "z" not allowed while "strict subs" in use at err line 25.

##</code><code>##

included from a:
included from b:
included from err:
Bareword "z" not allowed while "strict subs" in use at err line 25.

##</code><code>##

package L;

sub include {
    my $f = shift;
    my $r = do $f;
    unless (defined $r) {
        die "included from $f:\n$@" if $@;
    }
}

1;

##</code><code>##

use L;
...
L::include "a";
...
L::include "b";

##</code><code>##

error loading 'ERR': Bareword "z" not allowed while "strict subs" in use at ERR line 5.
stack trace:
   L::include called at D line 1
   L::include called at C line 1
   L::include called at B line 11
   L::bar called at B line 7
   L::foo called at B line 14
   L::include called at A line 2

##</code><code>##

package L;
use warnings;
use strict;
use File::Slurp;

sub include {
    my ($f) = @_;

    eval {
        my $e = eval qq(#line 1 "$f"\n) . read_file $f;
        die $@ if $@;
    };

    if ($@) {
        die $@
            if ref($@) ne '' or $@ =~ /stack trace:/s;

        my $max_depth = 30;
        my $err       = "error loading '$f': $@stack trace:\n";
        my $e         = -1;
        my @stack;
        my $i;
        for ($i = 0 ; $i < $max_depth ; ++$i) {
            my ($package, $filename, $line, $subroutine) = caller($i);
            last unless $package;

            # removing two evals below every include
            splice(@stack, -2, 2)
                if @stack > 2 and $subroutine eq "L::include";

            push(@stack, "   $subroutine called at $filename line $line");
        }
        $err .= join("\n", @stack, "");
        $err .= "...\n"
            if $i == $max_depth;
        die $err;
    }
}

1;