Implementations of SdlSchemaPluginBase::getSchemaDefinition, SchemaExtensionPluginInterface::getBaseDefinition, and SchemaExtensionPluginInterface::getExtensionDefinition should now return ?GraphQL\Language\Source rather than ?string

The underlying GraphQL library provides GraphQL\Language\Source which can be used to preserve filename and location information for the underlying SDL. This aids in debugging issues in the schema.

Previously SdlSchemaPluginBase::getSchemaDefinition, SchemaExtensionPluginInterface::getBaseDefinition, SchemaExtensionPluginInterface::getExtensionDefinition, and SdlSchemaExtensionPluginBase::loadDefinitionFile were implemented to return strings, but they now return Source instances.

If you're only using the default implementations from the GraphQL module or used SdlSchemaExtensionPluginBase::loadDefinitionFile with alternative file selection logic then there should be no action needed.

If you've overwritten any of these methods then you must update them to wrap the string in GraphQL\Language\Source instead, optionally adding filename information if it's available.