Backend CSS and JS don't get added when widget isn't loaded

[gmpf]

system/modules/multicolumnwizard/html/js/multicolumnwizard_be(_src).js
and
system/modules/multicolumnwizard/html/css/multicolumnwizard(_src).css
are intended to be loaded in the backend no matter whether a MultiColumnWizard widget is loaded or not, for example in case the field is initially hidden because it is part of a subpalette.

However, this doesn't happen because the addition of CSS and JS was rendered ineffectual by #213.

The asset paths are added to $GLOBALS['TL_CSS'] and $GLOBALS['TL_JAVASCRIPT'] in a parseTemplate hook:

MultiColumnWizard/system/modules/multicolumnwizard/MultiColumnWizardHelper.php

Lines 31 to 47 in 786f252

	public function addScriptsAndStyles(&$objTemplate)
	{
	//do not allow version information to be leaked in the backend login and install tool (#184)
	if ($objTemplate->getName() != 'be_login' && $objTemplate->getName() != 'be_install') {
	$GLOBALS['TL_JAVASCRIPT']['mcw'] = $GLOBALS['TL_CONFIG']['debugMode']
	? 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be_src.js'
	: 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be.js';
	$GLOBALS['TL_CSS']['mcw'] = $GLOBALS['TL_CONFIG']['debugMode']
	? 'system/modules/multicolumnwizard/html/css/multicolumnwizard_src.css'
	: 'system/modules/multicolumnwizard/html/css/multicolumnwizard.css';
	$objTemplate->ua .= ' version_' . str_replace('.', '-', VERSION) . '-' . str_replace(
	'.',
	'-',
	BUILD
	);
	}
	}

However, that hook is called from Template::parseTemplate after the head tags have already been rendered and added to the template in BackendTemplate::output:
https://github.com/contao/core/blob/d883f04807500b5f5c65bf9dd927c38e60812e42/system/modules/core/classes/BackendTemplate.php#L61-L92
Adding anything to those asset arrays in parseTemplate therefore has no effect.

I'm not sure about which way to go in solving this. I can see two approaches at the moment:

1. The addition of CSS and JS gets moved back to config.php and we detect the install/login pages differently. Something like this (untested):

// config.php
// …
$version = VERSION.'.'.BUILD;
$addBackendAssets = false;
if (version_compare($version, '4.0', '>='))
{
    $route = System::getContainer()->get('request_stack')->getCurrentRequest()->get('_route');
    if ($route !== 'contao_install' && $route !== 'contao_backend_login')
    {
        $addBackendAssets = true;
    }
}
elseif (TL_SCRIPT !== 'contao/install.php' && TL_SCRIPT !== 'contao/index.php')
{
    $addBackendAssets = true;
}

if (TL_MODE == 'BE' && $addBackendAssets)
{
    $GLOBALS['TL_JAVASCRIPT']['mcw'] = $GLOBALS['TL_CONFIG']['debugMode']
        ? 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be_src.js'
        : 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be.js';
    $GLOBALS['TL_CSS']['mcw']        = $GLOBALS['TL_CONFIG']['debugMode']
        ? 'system/modules/multicolumnwizard/html/css/multicolumnwizard_src.css'
        : 'system/modules/multicolumnwizard/html/css/multicolumnwizard.css';
}

Disadvantages: That's quite a few lines of logic for a config.php. Also, we'd be using deprecated constants (VERSION, BUILD), but then again, so does the rest of MCW. ;)

2. Essentially duplicate some of BackendTemplate::output to render the head tags and add them to the template after the fact:

// MultiColumnWizardHelper
// …
public function addScriptsAndStyles(&$objTemplate)
{
// …
        $js  = $GLOBALS['TL_CONFIG']['debugMode']
            ? 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be_src.js'
            : 'system/modules/multicolumnwizard/html/js/multicolumnwizard_be.js';
        $css = $GLOBALS['TL_CONFIG']['debugMode']
            ? 'system/modules/multicolumnwizard/html/css/multicolumnwizard_src.css'
            : 'system/modules/multicolumnwizard/html/css/multicolumnwizard.css';
        $objTemplate->javascripts .= \Template::generateScriptTag($js);
        $objTemplate->stylesheets .= \Template::generateStyleTag($css);
// …
}

Disadvantages: Duplication of core code. Also, I think we end up with those tags appearing twice if the widget is loaded as well.

[gmpf]

How to reproduce:

Add this to system/config/dcaconfig.php or app/Resources/contao/dca/tl_page.php:

$GLOBALS['TL_DCA']['tl_page']['subpalettes']['protected'] = 'groups,mcwIssue';

$GLOBALS['TL_DCA']['tl_page']['fields']['mcwIssue'] = [
 	'label'     => ['Test MCW issue',''],
	'inputType' => 'multiColumnWizard',
	'eval'      => [
		'columnFields' => [
			'col1'      => [
				'label'            => 'Foo or bar?',
				'inputType'        => 'select',
				'options'          => ['foo', 'bar']
			],
			'col2' => [
				'label'            => 'Baz or boing?',
				'inputType'        => 'select',
				'options'          => ['baz', 'boing']
			]
		]
	]
];

Edit any regular, non-protected page. If you look at the page source, you can see that the MultiColumnWizard CSS and JS aren't there.

Toggle the protected subpalette by selecting "Protect page" (de: "Seite schützen").

It looks like this in Contao 4.4:

Contao 3.5:

When the subpalette-triggering field is already saved as active, the MCW widget is generated and the CSS is loaded:

Contao 4.4 with CSS loaded:

Contao 3.5:

(The selects look kind of wrong as well, but that's a different issue.)