Only file JavaScript assets with preprocessing enabled can be optimized.

Problem/Motivation

An error is thrown, when a library is defined using "preprocess: false, but ommiting "minified":

example:
  version: 1
  remote: https://example.com
  license:
    name: Example
    url: https://example.com/license
    gpl-compatible: true
  js:
    js/script.js: { preprocess: false }

Error:

The website encountered an unexpected error. Please try again later.

Exception: Only file JavaScript assets with preprocessing enabled can be optimized. in Drupal\Core\Asset\JsOptimizer->optimize() (line 34 of core/lib/Drupal/Core/Asset/JsOptimizer.php).
Drupal\Core\Asset\JsCollectionOptimizerLazy->optimizeGroup() (Line: 183)
Drupal\system\Controller\AssetControllerBase->deliver()
call_user_func_array() (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 592)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext() (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 181)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 58)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 53)
Asm89\Stack\Cors->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 55)
Drupal\http_headers_cleaner\Middleware\HttpHeadersCleanerMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 704)
Drupal\Core\DrupalKernel->handle() (Line: 19)

This means, that the core forces the "minified" key for libraries not being preprocessed.

Further Information:
The problem seems to be
If the asset is not minified then it calls to optimize.
\Drupal\Core\Asset\JsCollectionOptimizer::optimize

                // Optimize this JS file, but only if it's not yet minified.
                if (isset($js_asset['minified']) && $js_asset['minified']) {
                  $data .= file_get_contents($js_asset['data']);
                }
                else {
                  $data .= $this->optimizer->optimize($js_asset);
                }

But if the preprocess is set to false, it throws an error, so the optimizers force the asset to be minified, and it gives a 500 Error when tries to load the asset.

\Drupal\Core\Asset\JsOptimizer::optimize

    if (!$js_asset['preprocess']) {
      throw new \Exception('Only file JavaScript assets with preprocessing enabled can be optimized.');
    }

Example from google_tag.libraries.yml

gtag:
  js:
    js/gtag.js: { preprocess: false }
  drupalSettings:
    gtag:
      tagId: null
      otherIds: []
      events: []
  dependencies:
    - core/drupalSettings

Steps to reproduce

• Install and configure the Google Tag Module
• Visit different pages to Trigger Google Tag
• Look at the recent log messages and see the error

Proposed resolution

Check if the js asset group should be optimized at all, before optimizing it.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet