let an http-exception object that ->can("as_psgi") recieve the psgi $…

…env as its first argument

lib/Plack/Middleware/HTTPExceptions.pm

@@ -47,7 +47,7 @@ sub transform_error {
 
     my($code, $message);
     if (blessed $e && $e->can('as_psgi')) {
-        return $e->as_psgi;
+        return $e->as_psgi($env);
     }
     if (blessed $e && $e->can('code')) {
         $code = $e->code;
@@ -123,7 +123,8 @@ the status message of the error code, such as I<Service Unavailable> for
 C<503>.
 
 Finally, the exception object may implement C<as_psgi>, and the result
-of this will be returned directly as the PSGI response.
+of this will be returned directly as the PSGI response.  When calling
+the C<as_psgi> method, the PSGI C<$env> will be passed.
 
 If the code is in the 3xx range and the exception implements the 'location'
 method (HTTP::Exception::3xx does), the Location header will be set in the

t/Plack-Middleware/httpexceptions-as_psgi.t

@@ -0,0 +1,41 @@
+use strict;
+use warnings;
+use Plack::Test;
+use HTTP::Request::Common;
+use Plack::Middleware::HTTPExceptions;
+use Test::More;
+
+{
+  package MyApp::Exception::Tuple;
+
+  sub new {
+    my ($class, @args) = @_;
+    return bless +{res => \@args}, $class;
+  }
+
+  sub as_psgi {
+    my ($self, $env) = @_;
+    Test::More::ok $env && $env->{'psgi.version'}, 
+      'has $env and its a psgi $env';
+    return $self->{res};
+  }
+}
+
+ok my $psgi_app = sub {
+  my $env = shift;
+  die MyApp::Exception::Tuple->new(
+    404, ['content-type'=>'text/plain'], ['Not Found']);
+};
+
+ok $psgi_app = Plack::Middleware::HTTPExceptions->wrap($psgi_app);
+
+test_psgi $psgi_app, sub {
+    my $cb = shift;
+    my $res = $cb->(GET "/");
+    is $res->code, 404;
+    is $res->content, 'Not Found';
+};
+
+# need to list the expected test number because of the test case in the
+# exception class.
+done_testing(5);