Storing StackTrace object in $env causes a circular reference.

The "real" fix for this would be to have an option or method to walk
over StackTrace frame and weaken() all args and lexicals (in case of
WithLexicals) so that the trace object can be safely stored in $env,
but for now, storing text version of the trace and HTML version would
be enough.

lib/Plack/Middleware/StackTrace.pm

@@ -28,10 +28,12 @@ sub call {
 
     if ($trace && ($caught || ($self->force && ref $res eq 'ARRAY' && $res->[0] == 500)) ) {
         my $text = trace_as_string($trace);
-        $env->{'plack.stacktrace'} = $trace;
+        my $html = $trace->as_html;
+        $env->{'plack.stacktrace.text'} = $text;
+        $env->{'plack.stacktrace.html'} = $html;
         $env->{'psgi.errors'}->print($text) unless $self->no_print_errors;
         if (($env->{HTTP_ACCEPT} || '*/*') =~ /html/) {
-            $res = [500, ['Content-Type' => 'text/html; charset=utf-8'], [ utf8_safe($trace->as_html) ]];
+            $res = [500, ['Content-Type' => 'text/html; charset=utf-8'], [ utf8_safe($html) ]];
         } else {
             $res = [500, ['Content-Type' => 'text/plain; charset=utf-8'], [ utf8_safe($text) ]];
         }
@@ -91,11 +93,10 @@ Plack::Middleware::StackTrace - Displays stack trace when your app dies
 =head1 DESCRIPTION
 
 This middleware catches exceptions (run-time errors) happening in your
-application and displays nice stack trace screen. The stack trace
-(L<Devel::StackTrace> or L<Devel::StackTrace::WithLexicals> object,
-depending on which library you have installed) is also stored in the
-environment under the key C<plack.stacktrace> so that middleware
-futher up the stack can reference it.
+application and displays nice stack trace screen. The stack trace is
+also stored in the environment as a plaintext and HTML under the key
+C<plack.stacktrace.text> and C<plack.stacktrace.html> respectively, so
+that middleware futher up the stack can reference it.
 
 This middleware is enabled by default when you run L<plackup> in the
 default I<development> mode.

t/Plack-Middleware/stacktrace.t

@@ -9,7 +9,7 @@ my $traceapp = Plack::Middleware::StackTrace->wrap(sub { die "orz" }, no_print_e
 my $app = sub {
     my $env = shift;
     my $ret = $traceapp->($env);
-    like $env->{'plack.stacktrace'}->as_string, qr/orz/;
+    like $env->{'plack.stacktrace.text'}, qr/orz/;
     return $ret;
 };