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[SR-7235] "nearly matches optional requirement" warning for correct function signature from protocol UICollectionViewDelegate #49783

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nevil opened this issue Mar 19, 2018 · 3 comments
Closed

[SR-7235] "nearly matches optional requirement" warning for correct function signature from protocol UICollectionViewDelegate #49783

nevil opened this issue Mar 19, 2018 · 3 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 4.2

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@nevil
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nevil commented Mar 19, 2018

Previous ID SR-7235
Radar rdar://problem/38641997
Original Reporter @nevil
Type Bug
Status Closed
Resolution Invalid
Environment

swift-DEVELOPMENT-SNAPSHOT-2018-03-17-a.xctoolchain
iOS SDK from Xcode 9.2:
Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, 4.2Regression
Assignee None
Priority Medium

md5: 422f3bbc92fab223281f16c055b6d033

relates to:

  • SR-7229 Unexpected ambiguity error

Issue Description:

The below code generates an unexpected warning as the function has a correct signature from UICollectionViewDelegate:

bug.swift:12:10: warning: instance method 'collectionView(_:cellForItemAt:)' nearly matches optional requirement 'collectionView(_:canFocusItemAt:)' of protocol 'UICollectionViewDelegate'
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

//

import UIKit

class ACollectionViewDelegate: NSObject, UICollectionViewDelegate {
    var collectionView: UICollectionView! { return UICollectionView() }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 0
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        return UICollectionViewCell()
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    }
}

Full invocation and output:

Apple Swift version 4.2-dev (LLVM cef3fe6d75, Clang bdc970d89c, Swift 931d06d1cc)
Target: arm64-apple-ios10.0
/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2018-03-17-a.xctoolchain/usr/bin/swift -frontend -c -primary-file SR-7235.swift -target arm64-apple-ios10.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -color-diagnostics -module-name main -o SR-7235.o
SR-7235.swift:12:10: warning: instance method 'collectionView(_:cellForItemAt:)' nearly matches optional requirement 'collectionView(_:canFocusItemAt:)' of protocol 'UICollectionViewDelegate'
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
SR-7235.swift:12:10: note: candidate has non-matching type '(UICollectionView, IndexPath) -> UICollectionViewCell'
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
SR-7235.swift:12:10: note: move 'collectionView(_:cellForItemAt:)' to an extension to silence this warning
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
SR-7235.swift:12:10: note: make 'collectionView(_:cellForItemAt:)' private to silence this warning
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
    private
UIKit.UICollectionViewDelegate:63:26: note: requirement 'collectionView(_:canFocusItemAt:)' declared here
    optional public func collectionView(_ collectionView: UICollectionView, canFocusItemAt indexPath: IndexPath) -> Bool
                         ^
@belkadan
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@swift-ci create

@nevil
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nevil commented Oct 29, 2019

Still occurring:

Apple Swift version 5.1 (swiftlang-1100.0.270.13 clang-1100.0.33.7)
Target: arm64-apple-ios10.0
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift -frontend -c -primary-file SR-7235.swift -target arm64-apple-ios10.0 -Xllvm -aarch64-use-tbi -enable-objc-interop -sdk /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -color-diagnostics -module-name main -o SR-7235.o
SR-7235.swift:12:10: warning: instance method 'collectionView(_:cellForItemAt:)' nearly matches optional requirement 'collectionView(_:canFocusItemAt:)' of protocol 'UICollectionViewDelegate'
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
SR-7235.swift:12:10: note: move 'collectionView(_:cellForItemAt:)' to an extension to silence this warning
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
SR-7235.swift:12:10: note: make 'collectionView(_:cellForItemAt:)' private to silence this warning
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
         ^
    private
UIKit.UICollectionViewDelegate:66:19: note: requirement 'collectionView(_:canFocusItemAt:)' declared here
    optional func collectionView(_ collectionView: UICollectionView, canFocusItemAt indexPath: IndexPath) -> Bool
                  ^

@nevil
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nevil commented Oct 29, 2019

Revisiting this I realized that this is my issue.
cellForItemAt delegate is from UICollectionViewDataSource, not UICollectionViewDelegate.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself regression swift 4.2
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@nevil @belkadan @AnthonyLatsis