What does the "exclude" Tag in Magento 2's view.xml file do

Question

The Magento 2 "blank" theme includes the following tag hierarchy.

<exclude>
    <item type="file">Lib::jquery/jquery-ui-1.9.2.js</item>
    <item type="file">Lib::jquery/jquery.ba-hashchange.min.js</item>
    <item type="file">Lib::jquery/jquery.details.js</item>
    <item type="file">Lib::jquery/jquery.details.min.js</item>
    <item type="file">Lib::jquery/jquery.hoverIntent.js</item>
    <item type="file">Lib::jquery/jquery.min.js</item>
    <item type="file">Lib::mage/captcha.js</item>
    <item type="file">Lib::mage/dropdown_old.js</item>
    <item type="file">Lib::mage/list.js</item>
    <item type="file">Lib::mage/loader_old.js</item>
    <item type="file">Lib::mage/webapi.js</item>
    <item type="file">Lib::moment.js</item>
    <item type="file">Lib::requirejs/require.js</item>
    <item type="file">Lib::date-format-normalizer.js</item>
    <item type="file">Lib::legacy-build.min.js</item>
    <item type="directory">Lib::modernizr</item>
    <item type="directory">Lib::tiny_mce</item>
    <item type="directory">Lib::varien</item>
    <item type="directory">Lib::jquery/editableMultiselect</item>
    <item type="directory">Lib::jquery/jstree</item>
    <item type="directory">Lib::jquery/fileUploader</item>
    <item type="directory">Lib::css</item>
    <item type="directory">Lib::lib</item>
    <item type="directory">Lib::extjs</item>
    <item type="directory">Lib::prototype</item>
    <item type="directory">Lib::scriptaculous</item>
    <item type="directory">Lib::mage/requirejs</item>
    <item type="directory">Lib::mage/adminhtml</item>
    <item type="directory">Lib::mage/backend</item>
    <item type="directory">Magento_Swagger::swagger-ui</item>
</exclude>

What is this here for. i.e. what's being excluded from what? Where and when does Magento 2 system code access this information?

Answer 1

Magento 2 supported bundling of js/html files. <exclude> node define list of resources that should not be bundled. see \Magento\Framework\View\Asset\Bundle\Manager for details

Answer 2

This configuration is accessed when you execute the command

bin/magento setup:static-content:deploy

In the function \Magento\Deploy\Model\Deployer::deployFile, the following two calls are of interest:

$this->assetPublisher->publish($asset);
$this->bundleManager->addAsset($asset);

The first call will add the asset file to the filesystem. I'm not sure what the second call does exactly. That's where I'm getting lost.

However, if you follow this second call, you will find some validation functions, which eventually lead to

// \Magento\Framework\Config\View

/**
 * Get excluded file list
 *
 * @return array
 */
public function getExcludedFiles()
{
    $items = $this->getItems();
    return isset($items['file']) ? $items['file'] : [];
}

/**
 * Get excluded directory list
 *
 * @return array
 */
public function getExcludedDir()
{
    $items = $this->getItems();
    return isset($items['directory']) ? $items['directory'] : [];
}

/**
 * Get a list of excludes
 *
 * @return array
 */
protected function getItems()
{
    $this->initData();
    return isset($this->data['exclude']) ? $this->data['exclude'] : [];
}

But, there are a few issues here.

First, the function \Magento\Framework\Config\View::getItems always seems to return an empty array.

Second, the function \Magento\Framework\View\Asset\Bundle\Manager::isExcludedFile will always return false

/**
 * Check if asset file is excluded
 *
 * @param string $filePath
 * @param LocalInterface $asset
 * @return bool
 */
protected function isExcludedFile($filePath, $asset)
{
    /** @var $asset LocalInterface */
    $filePathInfo = $this->splitPath($filePath);
    if ($filePathInfo && $this->compareModules($filePathInfo, $asset)) {
        return $asset->getSourceFile() == $filePathInfo['excludedPath'];
    }
    return false;
}

Because $asset->getSourceFile() is the absolute path to the asset file, while $filePathInfo['excludedPath'] is a relative path.

So, as far as I can see the the <exclude> configuration will not work anyway. But if it would work the asset would be excluded from the \Magento\Framework\View\Asset\Bundle.