[Theming] setting version and parent in theme.xml vs composer.json

[Vinai]

According to the documentation at http://devdocs.magento.com/guides/v1.0/frontend-dev-guide/themes/theme-create.html#fedg_create_theme_how-to_declare the theme should be registered using a theme.xml file.
From the next paragraph it seems that the theme composer.json file is optional and only required when then theme should be distributed and installable via composer.

Not too long ago creating a theme with just a theme.xml worked.
In the current release Magento ver. 0.42.0-beta1 however both the theme.xml AND the composer.json files are required.
There is no indication that is the case however. If one of the two files is missing, the theme simply does not show up in the admin.

This happens because the title and media attributes are read from the theme.xml and the version and parent are read from the composer.json.

Here the excerpt from \Magento\Framework\Config\Theme::_extractData():

        if (!empty($configContent)) {
            $dom = new \DOMDocument();
            $dom->loadXML($configContent);
            // todo: validation of the document
            /** @var $themeNode \DOMElement */
            $themeNode = $dom->getElementsByTagName('theme')->item(0);
            $data['title'] = $themeNode->getElementsByTagName('title')->item(0)->nodeValue;
            /** @var $mediaNode \DOMElement */
            $mediaNode = $themeNode->getElementsByTagName('media')->item(0);
            $previewImage = $mediaNode ? $mediaNode->getElementsByTagName('preview_image')->item(0)->nodeValue : '';
            $data['media']['preview_image'] = $previewImage;
        }

        if (!empty($composerContent)) {
            $json = json_decode($composerContent);
            $package = new Package($json);
            $data['version'] = $package->get('version');
            $parents = (array)$package->get('require', '/.+\/theme-/');
            $parents = empty($parents) ? null : array_keys($parents);
            $data['parent'] = empty($parents) ? null : array_shift($parents);
        }

I would prefer to simply do a pull request, but I'm unsure about the intended behaviour. Is this a bug or is it the intended behavior?
The theme.xsd indeed only references the title and media types.

Probably the reasoning behind moving the version and the parent theme into the composer.json file was that otherwise both files might become inconsistent. That makes sense, but at least to me it is ugly to require a composer.json file, even if the theme should not be distributed.

I think the most developer friendly process would be to keep the composer.json optional.

Please allow setting the version and the parent via the theme.xml file.
Then merge the composer.json settings.
Should the version or parent be set to a different value in the files, throw an exception.

This would be easy to implement, too.

---

On a side note:
The validators logging a message

'Field can't be empty' in .../app/code/Magento/Core/Model/Theme.php:326

is not very helpful without even the name of the field that can't be empty....

[nyov]

+1
Hadn't even noticed yet, but I second that. Being required to have some 3rd party boilerplate code like a composer.json in a theme sure doesn't look like the elegant way.

Please allow setting the version and the parent via the theme.xml file.
Then merge the composer.json settings.

That seems a sound idea.

[alankent]

Early on the design constraint was runtime of a store should not read from composer.json files so use of Composer is available but optional. This code violates that constraint so is a defect. The reason was also so we could migrate easily to a new packaging system in the future.

However, it is clear Composer is now mandatory and central to Magento. For dev beta we are saying "use git clone to play with the code". In production (at GA) it will be "only ever use composer so you know the exact version of what you are running, never git clone mainline".

I am going to investigate internally, but welcome any thoughts on whether you think its better to retain the original design constraint and potentially have some duplicated information (like version number) in composer.json and theme.xml or its better to only have the data once (but have a built in dependence on Composer).

I might write a quite note blog on the Composer interaction/model to expand.

[Vinai]

In my experience from training developers and frontend developers I am sure they would appreciate not having to create a composer.json in a theme that is only used within their company.

As written in the original post I think having potential duplicate information is preferable, especially if consistency is validated by displaying an appropriate error message in the admin area if version or parent theme don't match.
Anybody who wants to distribute their theme can simply omit the values in the theme.xml file.

[nyov]

I have no strong feelings either way, though from an integration perspective having the software depending on the packaging support system to know it's own components looks a bit off.

It's probably okay in the core code; requiring theme designers to know about composer semantics might be a bit much, though.

[antonmakarenko]

This change was done by accident and we are working to fix it.

Theme parent should be declared in theme.xml. Any information relevant to how a theme works, should be in theme.xml.

The composer.json file in theme is intended for packaging/distribution purposes only.

[alankent]

https://alankent.wordpress.com/2014/12/19/magento-2-composer-and-dependence-on-it-quick-note/ has some detail on the principle in case interesting to people (basically supporting what Anton just said).

[shivkumarsingh7]

any one got solution for create/list new theme in magento backend?

[Vinai]

WIthin the current develop branch you need to specify the parent and the version in the composer.json file, and the title and (optionaly) the preview file in the theme.xml file.

[shivkumarsingh7]

Hi @Vinai

following one is my app/design/frontend/Magento/magento2/theme.xml

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/Config/etc/theme.xsd">
    <title>Magento 2</title>
    <version>0.1.0</version>
    <parent>Magento/blank</parent>
    <media>
        <preview_image>media/preview.jpg</preview_image>
    </media>
</theme>

and following app/design/frontend/Magento/magento2/composer.json

{
    "name": "magento/magento2",
    "description": "N/A",
    "require": {
        "php": "~5.4.11|~5.5.0",
        "magento/theme-frontend-blank": "0.42.0-beta3",
        "magento/framework": "0.42.0-beta3",
        "magento/magento-composer-installer": "*"
    },
    "type": "magento2-theme",
    "version": "0.42.0-beta3",
    "license": [
        "OSL-3.0",
        "AFL-3.0"
    ],
    "extra": {
        "map": [
            [
                "*",
                "Magento/magento2"
            ]
        ]
    }
}

whats wrong I am doing here please help me to create custom theme. composer.json is copy of luma theme with some customization.