MigrationPluginManager::createInstances claims to throw a PluginException on invalid IDs, but does not

Testing to see what this breaks

So this seems to open up a whole can of worms before and after 📌 $migration_dependencies has inconsistent structure Fixed . Some of these tests just need an adjustment to expecting the exception instead of checking that createInstances returns an empty array. But more importantly, this shows migrations like the d6 block which has

migration_dependencies:
  required:
    - menu
    - d6_custom_block
    - d6_user_role

There is no 'menu' migration. There are d6_menu and d7_menu migrations. But the plugin manager pumps the migration_requirements through expandPluginIds before building the requirements array, and thus stripping out any non-existent migrations. So migrations requirements check that migrations that exist have run to completion, but never checks that the migrations listed in the requirements actually exist. If they don't exist, they are just skipped over...

Appears to have test failures.

Have not yet reviewed

Yeah, I'm still working through the ramifications of all this, trying to see if we can fix it, or if we are going to need to add in a BC layer.

Sigh.. it's never good when it's down to just the full upgrade tests failing.. mean something isn't being tested at the kernel level that should be..

My mistake, those aren't the primary full upgrade tests, those are the full upgrade tests for the forum module. Those failures come from not enabling the language module despite the language migration being required for some of the migrations being run. The test itself will need a few updates to pass with that module enabled, which I will try to work through.