Warn people if neither core nor the module were installed with composer, so the dependencies are not available

Not sure that's right place to throw exception, and log it... because exception will be logged anyway

Meantime better to add hook_requirements to do this check

+++ b/src/Plugin/DMU/Indexer/Functions.php
@@ -49,6 +49,11 @@ class Functions extends IndexerBase implements IndexerExecutionInterface, Indexe
+    if (!class_exists('Pharborist\Parser')) {

I bet it will not work because class_exists will not call autoloader

If I understand this right, this will happen to someone who (a) does not install their Drupal 8 site with composer (b) did not install their drupalmoduleupgrader with composer either, but (d) drush dl-ed the module or had a git checkout of it.

I think its a fine improvement for that case.

Huh, I pulled the trigger too fast. Let's discuss.

composer 1.6.3 is what I'm running and Drupal 8.8.x core does not allow me to do a composer up from the drupal core folder
however I can do a composer up from the drupalmoduleupgrader

Drupal 8.7.x did not have this problem with composer version 1.6.3 (default version provided with Ubuntu 18.04 LTS)

I don't know how would composer figure out what to do if the directory you are running it is not managed by composer. What does composer update mean then? How did it work with 8.7.x with a non-composer Drupal core setup?

It's pretty agressive when we're forced to use the bleeding edge ALL the time, maybe they will fix this before 8.8.x is released.
(it's still in dev)
a lot of people will have the same issue I have when 8.8.0 is released unless the core maintainers fix this.

What should be fixed in core? To be able to run composer update from a non-composer managed directory? If you git checkout a Drupal module into your repo how would composer know it is there and it needs to manage it? It did not even install it in the first place.

The previous version of the readme suggested using https://www.drupal.org/project/composer_manager to merge core composer with module composer data so its managed within the high level composer file, but as you can see on that project it is deprecated since Drupal 8.1 (3.5 years ago) because core provides the necessary pieces to require modules as composer dependencies.

I don't contest that this improves the situation if composer was not yet used with the module. Let's get this in and then see what people say with the new release.

#3075785: Update composer/composer to ^1.9.1 has some background info, if you are installing Drupal core with composer then 1.9.0 is not required, just if you are developing core, which is the case if you use a git checkout rather than installing Drupal with composer.