Invalid service backend alias when a driver returns null for driver or databaseType

Why would those method return null? I see it’s technically possible, but wouldn’t return type hinting or annotations do a better job in narrowing the type?

type hinting? yes. But we would need to wait for 12.x then?

it’s technically possible, quite improbable, that's why I marked this as minor.

Well, not if we had 📌 Introduce a @return-type-will-be-added annotation to indicate return type addition in next major; enforce with a PHPStan rule Active … we would be able to typehint the classes extending Connection.

@mondrake ghost of drupal past explained another way to reproduce the bug, more realistic, which is not influenced by what connection holds. Added another unit test for covering that.

So even if what you suggest would work in that case (and I hope we can start doing that all over core), wouldn't work on this one.

1) Drupal\Tests\Core\DependencyInjection\Compiler\BackendCompilerPassTest::testProcess
Expectation failed for method name is "hasDefinition" when invoked 1 time
Parameter 0 for invocation Symfony\Component\DependencyInjection\ContainerBuilder::hasDefinition('.fakeService'): bool does not match expected value.
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'a_valid_default_backend.fakeService'
+'.fakeService'
/builds/issue/drupal-3518917/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php:67
/builds/issue/drupal-3518917/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php:101
FAILURES!

Shows the test coverage

Summary appears to match the MR and don't see any open questions.

Committed/pushed to 11.x and cherry-picked to 11.2.x, thanks!

catch → closed merge request !11810