Flaky error handling with MaskErrors

[Speedy1991]

The ValidationCache is writing any errors in the execution_context.errors

    def on_validate(self) -> Iterator[None]:
        execution_context = self.execution_context

        errors = self.cached_validate_document(
            execution_context.schema._schema,
            execution_context.graphql_document,
            execution_context.validation_rules,
        )
        execution_context.errors = errors
        yield

But MaskErrors is checking for self.execution_context.result.errors

    def on_operation(self) -> Iterator[None]:
        yield
        result = self.execution_context.result
        if result and result.errors:

Maybe this bug is in other extensions too?

[Speedy1991]

It would be also nice to have a helper function on SchemaExtension to easily add errors. I saw the ValidatioRule has an report_error, something simmelar would be also nice in SchemaExtension.

My current workaround is a helper function:

def _inject_exception(execution_context: ExecutionContext, error: Exception):
    if not execution_context.result:
        execution_context.result = ExecutionResult()
    if execution_context.result.errors is None:
        execution_context.result.errors = list()
    execution_context.result.errors.append(GraphQLError(str(error), original_error=error))