[Dancer2 0.200003] Weird behaviour with Plugin Inclusion

[pierre-vigier]

Hi,

i got an app that was working on Dancer 0.166001 and is breaking with 0.200003 .
Here is a trimmed down version of the problem. Once including Dancer2::Plugin::Database , i get a Can't locate object method "dsl" via package "DemoApp" error message

• bin/app.psgi

#!/usr/bin/env perl
use strict;
use warnings;
use lib 'lib';
use DemoApp;

return DemoApp->to_app;

*lib/DemoApp.pm

package DemoApp;
use DemoApp::Extension;
use Dancer2;

get '/' => sub { return 'root' };

true;

*lib/DemoApp/Extension.pm

package DemoApp::Extension;
use Dancer2 appname => 'DemoApp';
use Dancer2::Plugin::Database;

get '/extension' => sub { 'extension'; };

That code runs on Dancer2 0.166001, but not on 0.200003.

Fix is pretty simple, in my code, if i reverse in lib/DemoApp.pm the inclusion of Dancer2 and DemoApp::Extension, it is then working as expected:

package DemoApp;
use Dancer2;
use DemoApp::Extension;

instead of

package DemoApp;
use DemoApp::Extension;
use Dancer2;

It might be worth a hint in documentation for people upgrading from a version below 0.200001 to 0.200001 and above.

The code is working properly in 0.200001 and above if in my case the DemoApp::Extension package do not include plugin Dancer2::Plugin::Database .
I can't tell if it's a bug of Dancer2 or of my code, but it's a breaking change. That's happening with other plugin as well, like Dancer2::Plugin::Email.

[xsawyerx]

What version of the plugins are you using?

[pierre-vigier]

Should be the last ones,
Dancer2::Plugin::Database => 2.16
Dancer2::Plugin::Email => 0.003

> perl -I local/lib/perl5 -MDancer2::Plugin::Database -E 'say $Dancer2::Plugin::Database::VERSION;'
2.16
>perl -I local/lib/perl5 -MDancer2::Plugin::Email -E 'say $Dancer2::Plugin::Email::VERSION;'
0.0003

[xsawyerx]

Preliminary debugging shows that the problem is due to the order here:

• You load DemoApp
• This first loads another class: DemoApp::Extension.
• It registers an app called DemoApp.
• It then loads a plugin which will try to use the dsl keyword in DemoApp namespace.

Because DemoApp itself hasn't run use Dancer2 yet, it will not have that DSL keyword (or any other DSL keywords) available yet. They will only get used when you call use Dancer2 inside that class.

You're basically calling a plugin that tries to use keywords for a class that did not import them yet.

[xsawyerx]

This might work if we shift the call for keywords on the calling class rather than on the app's name as class, but I'm not sure if we can reach it. caller is probably not reliable once you have plugins within plugins. We can use the old trick of trying to find dsl in it. I'm not sure that's correct design though. (Do we allow someone to define "dsl" somewhere in the hierarchy without it being a Dancer2 app?)

[pierre-vigier]

I understood the issue, and i already fixed it in my code.
My only concern being that it worked before, i guess an hint in the documentation could be enough, as it makes perfect sense. That's why i am thinking it should probably not considered as a bug. Maybe, if possible, an hint would be enough

[xsawyerx]

I'm trying to see whether we can really fix it, as in you wouldn't need to change any order. :)

[xsawyerx]

The following patch in Dancer2::Plugin will sort this out, no matter what your order is:

-                foreach my $keyword ( keys %{$_[0]->app->name->dsl->dsl_keywords} ) {
+                my $app_dsl_cb;
+                ## no critic qw(ControlStructures::ProhibitCStyleForLoops)
+                for ( my $i = 0; my $caller = caller($i); $i++ ) {
+                    $app_dsl_cb = $caller->can('dsl')
+                        and last;
+                }
+
+                $app_dsl_cb
+                    or croak('Could not find Dancer2 app');
+
+                foreach my $keyword ( keys %{ $app_dsl_cb->()->dsl_keywords} ) {

I'll prepare a pull request for this.

[pierre-vigier]

Nice!

[xsawyerx]

Thank you for raising this issue. :)

[xsawyerx]

Pull request created. :)

[xsawyerx]

Merged and will be released soon. Thanks for reporting the issue.

[pierre-vigier]

Thanks for the fix