[SR-6417] Check if super is called when required.

[swift-ci]

Previous ID	SR-6417
Radar	rdar://problem/17408107
Original Reporter	WWessels (JIRA User)
Type	Improvement

Additional Detail from JIRA

Votes	5
Component/s	Compiler
Labels	Improvement, LanguageFeatureRequest, StarterProposal
Assignee	mb (JIRA)
Priority	Medium

md5: 8ca04a71f5feba734a5bda3679466acc

Issue Description:

When creating a subclass of NSObject, you get an error when you 'forget' to call super in the init() function.

When creating a subclass of UIViewController, and you forget to call super in viewDidLoad, viewWillAppear, etc, you will not get an error or warning.

When creating a subclass of UIView, and you forget to call super in your implementation of awakeFromNib, you will not get an error or warning.

When creating a subclass of UITableViewCell or UICollectionViewCell, and you forget to call super in your implementation of prepareForReuse, you will not get an error or warning.

And there are probably more places where it is required, but not guarded that you call super.

As a freelancer, I produce and see lots of code and this is one of the issues that I often see (and fix). Forgetting to call super in these functions results in unexpected behaviour, even crashes and it can be pretty hard to find the problem.

It would be very helpful if one could declare that an overriding function has to call super. For instance with an attribute in the same manner as @discardableResult:

@callToSuperRequired
func viewDidLoad() {

}

This attribute should be valid for all subclasses that override this function, even subclasses of subclasses.

And then Apple should use this in their declaration of the aforementioned functions.

[belkadan]

We actually have this in Objective-C as the objc_requires_super attribute. Implementing this in Swift means:

• coming up with a name for it

• proposing it on swift-evolution (it's probably come up before? can't remember)

• adding the new attribute - easy

• adding some checking for it (syntactic? path-sensitive?) - a bit harder

• making sure it gets imported from Objective-C - easy again, we do the same for other attributes