swiftlang/swift

[SR-7301] Bad fixit suggested for protocol extension implementation for inherited objc protocol

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#49,849 opened on Mar 28, 2018

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Description
Previous ID SR-7301
Radar None
Original Reporter kdawgwilk (JIRA User)
Type Bug

Attachment: Download

Xcode 9.2

Swift 4

macOS 10.13.3
Votes 0
Component/s Compiler
Labels Bug, StarterBug
Assignee None
Priority Medium

md5: f483fe309b1876278257725a1dc2b1b5

relates to:

  • SR-3349 @objc methods cannot be contained in protocol extensions

Issue Description:

I have the following code that has a compiler error

@objc protocol IntroAnimationController: UIViewControllerAnimatedTransitioning {
    func frame(for view: UIView, fromView: UIView) -> CGRect
    func animations(fromView: UIView, toView: UIView) -> () -> Void
}

extension IntroAnimationController {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.20
    }
}

The error says:

![](Screen Shot 2018-03-28 at 3.47.33 PM.png)

and includes a fixit that that turns my code into this:

extension IntroAnimationController {
    @objc(transitionDuration:) func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.20
    }
}

And then gives me these two wonderful new errors:

![](Screen Shot 2018-03-28 at 3.46.32 PM.png)

None of the fixits are helpful and the error message does not give me any clue why I can't do this

Contributor guide

Research direction
Investigate the fix it generation logic in the Swift compiler for protocol extensions that inherit from @objc protocols. The issue involves a fixit that incorrectly suggests adding @objc(transitionDuration:) which leads to further errors. Look at how the compiler handles conformance to @objc protocols in extensions.
Tech stack
swift
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Swift
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80