Throw an exception if double rendering is attempted

Changes

@@ -1,5 +1,6 @@
 
-9.25  2022-04-19
+9.25  2022-04-25
+  - Improved Mojolicious::Renderer to throw an exception if rendering is attempted more than once.
 
 9.24  2022-04-18
   - Improved Mojo::Headers to output headers in a canonical order.

lib/Mojolicious/Renderer.pm

@@ -1,6 +1,7 @@
 package Mojolicious::Renderer;
 use Mojo::Base -base;
 
+use Carp qw(croak);
 use Mojo::Cache;
 use Mojo::DynamicMethods;
 use Mojo::File qw(curfile path);
@@ -123,6 +124,9 @@ sub render {
 sub respond {
   my ($self, $c, $output, $format, $status) = @_;
 
+  my $stash = $c->stash;
+  croak 'A response has already been rendered' if $stash->{'mojo.respond'}++ && $stash->{'mojo.respond'};
+
   # Gzip compression
   my $res = $c->res;
   if ($self->compress && length($output) >= $self->min_compress_size) {

t/mojolicious/renderer.t

@@ -145,6 +145,14 @@ ok !$c->res->headers->vary,             'no "Vary" value';
 ok !$c->res->headers->content_encoding, 'no "Content-Encoding" value';
 is $c->res->body, $output, 'same string';
 
+subtest 'Response has already been rendered' => sub {
+  my $c = $app->build_controller;
+  $c->render(text => 'First call');
+  is $c->render_to_string(text => 'Unrelated call'), 'Unrelated call', 'right result';
+  eval { $c->render(text => 'Second call') };
+  like $@, qr/A response has already been rendered/, 'right error';
+};
+
 # Missing method (AUTOLOAD)
 my $class = ref $first->myapp;
 eval { $first->myapp->missing };