Add a configuration exporter

Adding the CMI 2.0 issue tag.

If you are going to use a StorageComparer for this consider reviewing the following issue:
#2993271: Remove unused ConfigManager dependency in StorageComparer

Oh! I didn't mean to un-assign you! But there was nothing I could do.

1. +++ b/core/lib/Drupal/Core/Config/ArchiveStorage.php
   @@ -0,0 +1,258 @@
   +  public function delete($name) {
   

   yea this is not great. But unfortunately with the ArchiveTar there is not much we can do.
   Maybe we can postpone the ArchiveStorage and implement the exporter without it.

2. +++ b/core/lib/Drupal/Core/Config/ConfigExporter.php
   @@ -0,0 +1,84 @@
   +  public function export() {
   

   this whole code would be in the first instance just StorageCopier::copyConfig() #3016429: Add a config storage copy utility trait and fix ConfigManager::createSnapshot, but it is where the transformer api will be called.

3. +++ b/core/modules/config/src/Controller/ConfigController.php
   @@ -19,18 +20,18 @@
   -   * The target storage.
   +   * The active storage.
   ...
   -  protected $targetStorage;
   +  protected $activeStorage;
   ...
   -   * The source storage.
   +   * The synchronization storage.
   ...
   -  protected $sourceStorage;
   +  protected $syncStorage;
   

   I approve of this very much!

4. +++ b/core/modules/config/src/Controller/ConfigController.php
   @@ -90,16 +102,18 @@ public function __construct(StorageInterface $target_storage, StorageInterface $
      public function downloadExport() {
        file_unmanaged_delete(file_directory_temp() . '/config.tar.gz');
   ...
   -    $archiver = new ArchiveTar(file_directory_temp() . '/config.tar.gz', 'gz');
   +    $archive = new ArchiveTar(file_directory_temp() . '/config.tar.gz', 'gz');
   +    $target = new ArchiveStorage($this->fileSystem, $archive);
        // Get raw configuration data without overrides.
        foreach ($this->configManager->getConfigFactory()->listAll() as $name) {
   -      $archiver->addString("$name.yml", Yaml::encode($this->configManager->getConfigFactory()->get($name)->getRawData()));
   +      $target->write($name, $this->configManager->getConfigFactory()->get($name)->getRawData());
        }
        // Get all override data from the remaining collections.
   -    foreach ($this->targetStorage->getAllCollectionNames() as $collection) {
   -      $collection_storage = $this->targetStorage->createCollection($collection);
   -      foreach ($collection_storage->listAll() as $name) {
   -        $archiver->addString(str_replace('.', '/', $collection) . "/$name.yml", Yaml::encode($collection_storage->read($name)));
   +    foreach ($this->activeStorage->getAllCollectionNames() as $collection) {
   +      $collection_source = $this->activeStorage->createCollection($collection);
   +      $collection_target = $target->createCollection($collection);
   +      foreach ($collection_source->listAll() as $name) {
   +        $collection_target->write($name, $collection_source->read($name));
          }
        }
   

   This is where I think we could improve things already even without the archive storage but by using the active storage instead of the config manager. This would allow us to simply call the transformer first.

   so the code here would be:

     /**
      * Downloads a tarball of the site configuration.
      */
     public function downloadExport() {
       file_unmanaged_delete(file_directory_temp() . '/config.tar.gz');
   
       $archiver = new ArchiveTar(file_directory_temp() . '/config.tar.gz', 'gz');
       
       $storage = $this->activeStorage;
       
       // Get raw configuration data without overrides.
       foreach ($storage->listAll() as $name) {
         $archiver->addString("$name.yml", Yaml::encode($storage->read($name)));
       }
       // Get all override data from the remaining collections.
       foreach ($storage->getAllCollectionNames() as $collection) {
         $collection_storage = $storage->createCollection($collection);
         foreach ($collection_storage->listAll() as $name) {
           $archiver->addString(str_replace('.', '/', $collection) . "/$name.yml", Yaml::encode($collection_storage->read($name)));
         }
       }
   
       $request = new Request(['file' => 'config.tar.gz']);
       return $this->fileDownloadController->download($request, 'temporary');
     }
   

   This way we could replace $storage = $this->activeStorage; with $storage = $this->storageTransformer->transformExport('config.storage.sync'); (or 'config.storage.tarball' etc..)

Rerolled the patch in #8 and removed the ArchiveStorage and ArchiveStorageTest files as per point 4 in #9.
Also, I tried

  \Drupal::service('config.exporter')->export();

executing in devel and the configuration was exported successfully.

As @bircher mentioned in point #4 that replace ,

+++ b/core/lib/Drupal/Core/Config/ConfigExporter.php
@@ -0,0 +1,84 @@
+  public function export() {

this whole code would be replaced with static method replaceStorageContents of StorageCopyTrait.

As this export() function is exporting all configuration and then put it in an archive, but what if any contrib modules wishing to export only some set of configuration for example (system.site and user.settings). In that case we can receive set of configuration which needs to be export in export() function as argument as shown in patch.

So now we can export all configuration as well as particular set of configuration or single configuration and then put it in an archive.

I think we can close this as a duplicate of #3036193: Add ExportStorage to allow config export in third party tools

While it is not strictly the same, the exporter here would be quite trivial:

namespace Drupal\Core\Config;

class ConfigExporter {
  use StorageCopyTrait;

  protected $export;
  protected $sync;

  public function __construct(StorageInterface $export, StorageInterface $sync) {
    $this->export = $export;
    $this->sync = $sync;
  }

  public function export() {
    self::replaceStorageContents($this->export, $this->sync);
  }
}

with the service definition:

  config.exporter:
    class: Drupal\Core\Config\ConfigExporter
    arguments: ['@config.storage.export', '@config.storage.sync']

See the change notice https://www.drupal.org/node/3037022

I am not sure what a service would be used for other than just calling it from a cli command or maybe in the future from a button in the UI, but then I think we can do that there. #14 suggests that more features would be expected so I think we should open a new issue and scope out the requirements first. The requirements we had planned in this issue have been met.