[Form] DependencyInjectionExtension Type extension exception

[7ochem]

Symfony version(s) affected: 4.2.0 and above (currently up until 5.1)

Description
The getTypeExtensions($name) method of \Symfony\Component\Form\Extension\DependencyInjection\DependencyInjectionExtension throws a strange exception message:

The extended type specified for the service "0" does not match the actual extended type. Expected "Vendor\Bundle\AcmeBundle\Form\FooType", given "Vendor\Bundle\AcmeBundle\Form\BarType".

See the hightlighted code lines of the getTypeExtensions() method in the additional context below, the $serviceId variable contains the integer key of the items of the $this->typeExtensionServices[$name] iterable. Apparently, this has been set to an actual service ID by a service ID guesser before Symfony went full FQCN and now it just remains a numeric key. But the thrown exception message has not been adjusted to the new situation. This results is a very unclear error.

How to reproduce
Have a Type extension's getExtendedType(s) return invalid type(s)

Possible Solution
Clarify the exception message with useful data. Also the key in the loop is therefore probably no longer needed.

Additional context

symfony/src/Symfony/Component/Form/Extension/DependencyInjection/DependencyInjectionExtension.php

Lines 64 to 78 in 4170346

	if (isset($this->typeExtensionServices[$name])) {
	foreach ($this->typeExtensionServices[$name] as $serviceId => $extension) {
	$extensions[] = $extension;
	$extendedTypes = [];
	foreach ($extension::getExtendedTypes() as $extendedType) {
	$extendedTypes[] = $extendedType;
	}
	// validate the result of getExtendedTypes() to ensure it is consistent with the service definition
	if (!\in_array($name, $extendedTypes, true)) {
	throw new InvalidArgumentException(sprintf('The extended type specified for the service "%s" does not match the actual extended type. Expected "%s", given "%s".', $serviceId, $name, implode(', ', $extendedTypes)));
	}
	}
	}

[xabbuh]

I think #36613 will provide a more helpful message.