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[SR-7348] Using symbols in protocol extensions doesn't always check where-clauses for allowable symbols. #49896

swift-ci opened this issue Apr 4, 2018 · 1 comment


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swift-ci commented Apr 4, 2018

Previous ID SR-7348
Radar None
Original Reporter CTMacUser (JIRA User)
Type Bug
Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug
Assignee None
Priority Medium

md5: 814da93b5b8c456ddd7f8b62a26aac10

Issue Description:

Start with:

public enum InvertedRange<Index: Comparable> {
    case beforeStart, afterEnd, all
    case prefix(upThrough: Index)
    case range(after: Index, upThrough: Index)
    case suffix(after: Index)

public protocol TransferableCollection: MutableCollection /*[[1]]*/ where /*[[2]]*/ Self.SubSequence: TransferableCollection {}

extension TransferableCollection /*[[3]]*/ {

    private func convertRange(_ range: InvertedRange<Index>) -> Range<Index>
    { /*...*/ }

    private func convertRange<R>(_ range: R) -> InvertedRange<Index> where R: RangeExpression, R.Bound == Index {
        let r = range.relative(to: self)
        switch (r.lowerBound, r.upperBound) {
        case (startIndex, endIndex): return .all
        case (startIndex, startIndex): return .beforeStart
        case (startIndex, let i): return .prefix(upThrough: index(before: i)) // ERROR HERE
        case (let i, endIndex): return .suffix(after: index(before: i)) // AND HERE
        case (endIndex, endIndex): return .afterEnd
        case (let s, let e): return .range(after: index(before: s), upThrough: index(before: e)) // AND HERE


Where there are three errors at the lines that call the base BidirectionalCollection method, index(before: ). The error is:

Argument labels '(before:)' do not match any available overloads 

This can be remedied by replacing comment-spot #3 with:

where Self: BidirectionalCollection 

But I should be able to do that in the primary definition. If I put comment-spot #3 back into a comment and replace comment-spot #2 with:

Self: BidirectionalCollection,

it should also correct the problem, but it doesn't. Worse, putting the declaration in comment-spot #3 again this time does not fix it!

However, if I turn comment-spots #2 and #3 back into comments, and replace comment-spot #1 with:

, BidirectionalCollection

Then the code in the extension block works. (Putting the where-clause back in comment-spot #3 doesn't change anything this time.)

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belkadan commented Apr 5, 2018

cc @huonw

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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