[SR-15176] Fixit for override func that should be override var

[CodaFi]

Previous ID	SR-15176
Radar	rdar://28337871
Original Reporter	@CodaFi
Type	Improvement

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Improvement, DiagnosticsQoI, StarterBug
Assignee	jiaren wang (JIRA)
Priority	Medium

md5: b17661d61829d04b65f822d78b07388a

Issue Description:

Consider

class C {
  var canBecomeFirstResponder: Bool

  init() {}
}

class D: C {
    override func canBecomeFirstResponder() -> Bool {
    }
}

We should add a special case to diagnoseGeneralOverrideFailure that tries to see if it can correct no-args FuncDecls to VarDecls and vice-versa.

[swift-ci]

Comment by jiaren wang (JIRA)

I would like give a shot on this. Could I get some hint?

[LucianoPAlmeida]

If I understand it correctly, the idea it here https://github.com/apple/swift/blob/a3c7d6c13984d884ccce80df88b950f0723a3af0/lib/Sema/TypeCheckDeclOverride.cpp#L540 somehow try to detect cases where you have a property trying to override a no-args function on base class or vice versa and try to provide a fix-it to provide a fix it for making one into another. For example, the fix-it offered will make the func in the example be

class D: C {
   - override func canBecomeFirstResponder() -> Bool {
   - }
   + override var canBecomeFirstResponder: Bool {
   + }
}

Since the override attempt have the same name and the same is a no-args function that produce the same result as the base class property (Bool).

[danielfalbo]

Swift Mentorship program mentee here, trying to contribute for the first time. Will dive deeper and work on this 😁

[RAJAGOPALAN-GANGADHARAN]

Hello @AnthonyLatsis - is this issue still open, can I give it a shot? Thanks!

[AnthonyLatsis]

You’re welcome to! Make sure it still reproduces though. Want we to assign you?

[danielfalbo]

I got busier and did not complete it yet, but I did make progress on this and was planning on opening the PR soon.

https://github.com/danielfalbo/swift/tree/fixit-override-func-that-should-be-override-var

[danielfalbo]

Update: I don’t think I’ll keep working on this anytime soon, I’m unassigning myself

[Rajveer100]

Let's try this!

[Rajveer100]

Hey @LucianoPAlmeida @AnthonyLatsis , I managed to find the error call site:
File --> /lib/Sema/TypeCheckDeclPrimary.cpp

(Case 1: When the method is overridden instead of the property)

FD->diagnose(diag::method_does_not_override, isClassContext)
                .highlight(OA->getLocation());

(Case 2: When the property is overridden instead of the method)

VD->diagnose(diag::property_does_not_override, isClassContext)
                .highlight(OA->getLocation());

So I think fixing the actual issue remains. I will try to do it!

[Rajveer100]

@AnthonyLatsis I have a little off-topic issue, I have come across this earlier too, what I did was to delete my workspace and again create it, but is there any other solution to this?

<unknown>:0: error: compiled module was created by an older version of the compiler; rebuild 'Swift' and try again:

[Rajveer100]

PS: Rebuilding fixed the problem!

[AnthonyLatsis]

is there any other solution to this?

This means the binary module format version associated with the just-built compiler is different than the one that was used to serialize the Standard Library (the Swift module). Most likely, you pulled in the latest changes and rebuilt just the compiler (swift-frontend) rather than everything, including the Standard Library. Re-creating the workspace is almost never the answer, because the workspace or the generated Xcode projects are not responsible for building anything — the Ninja build is.

[Rajveer100]

Yes, also one more thing, I am suddenly encountering problems with syntax colouring and type hints not working properly in Xcode files while I am making changes, I tried clearing ~/Library/Developer/Xcode/DerivedData folder too, which could potentially re-index the files, but this isn't still working...

(Some of the text is white, while some of them green, and some are showing few function type hints, not all)

[AnthonyLatsis]

I have always seen these functional issues come up randomly when navigating the code base in Xcode. They usually get worse the older and more outdated the generated project becomes. Re-generating the projects after every checkout is probably the right answer, but I wouldn’t know for certain: I am too lazy to always keep the generated projects in sync, and tend to fall back to searching or spawning tabs whenever these issues show up.

[Rajveer100]

Also, are there any docs related to these specific types of files, meaning, learning about the Types, Decl, etc, to grab the pointers for exactly what I am looking for, or do I have to manually learn and figure out?

[Rajveer100]

Like in this issue, I will have to find a match for the function parameter and its declaration in the parent class, to correctly identify whether this override can be fixed...same goes for the property...

[LucianoPAlmeida]

Like in this issue, I will have to find a match for the function parameter and its declaration in the parent class, to correctly identify whether this override can be fixed...same goes for the property...

There is a little bit of info here

[Rajveer100]

Hey thanks a lot @LucianoPAlmeida! Looks like Swift Forums is a good place for asking such doubts!

[LucianoPAlmeida]

There is a compiler category on the forums where you can ask more general questions about development in the compiler.
But if those are related to the issue is fine to keep the discussion here or on PRs =]

[Rajveer100]

Cool!

[AnthonyLatsis]

actually when I was looking for type hint

What do you mean by "type hint"? Code completion hints?

Also, are there any docs related to these specific types of files, meaning, learning about the Types, Decl, etc, to grab the pointers for exactly what I am looking for, or do I have to manually learn and figure out?

I do not know of any detailed write-ups on the AST design or the parts of semantic analysis that do not involve subtle and complex algorithms among our docs. This is where the inline documentation and comments come in handy. But we do have a list of external resources, many of which I found very helpful back in the day, with many more yet to read. Check out the article by Slava Pestov about how things are represented in the compiler.

[Rajveer100]

Thanks! @AnthonyLatsis
I will go through the external resources!

Why was this issue closed and re opened?

[Rajveer100]

I have added the notes in the diagnostic file, I hope the changes are relatively fine:
Commits

[AnthonyLatsis]

Have you tested them? Please open a pull request if you want your changes to be reviewed.

[Rajveer100]

Coming soon!

[Rajveer100]

I have one question, regarding the super class inherit, should we consider the case for only one base class or can it be multiple classes, like, for example, class D could inherit from two classes B and C, where the function | property could be from either of them...Maybe an idea would be to limit the number of inherited types to be 2 or 3 considering optimisation?

[Rajveer100]

I finally managed to do it! I just need to provide a fixit now!

Here is the output:

error: method does not override any method from its superclass
    override func canBecomeFirstResponder() -> Bool {
    ~~~~~~~~      ^
note: did you mean to override the property 'canBecomeFirstResponder'?
    override func canBecomeFirstResponder() -> Bool {
                  ^

[AnthonyLatsis]

I have one question, regarding the super class inherit, should we consider the case for only one base class or can it be multiple classes

Swift does not have multiple inheritance.

[Rajveer100]

Oops! My bad! I misinterpreted it with C++ as it has the 'virtual' keyword to handle the diamond problem.

[wesleykebrown]

Hi @CodaFi. I'm working in a full-stack development cohort with a requirement for an open source contribution. I would love to try this one as my first one as I have an interest in learning Swift.

[AnthonyLatsis]

@wesleykebrown Assigned you.