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[SR-11725] No fixit to add stubs when conforming to Sequence or Collection #54134

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NevinBR opened this issue Nov 6, 2019 · 3 comments
Open

[SR-11725] No fixit to add stubs when conforming to Sequence or Collection #54134

NevinBR opened this issue Nov 6, 2019 · 3 comments
Labels
associated type inference bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself conformances Feature → protocol: protocol conformances diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@NevinBR
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NevinBR commented Nov 6, 2019

Previous ID SR-11725
Radar rdar://problem/56966686
Original Reporter @NevinBR
Type Bug
Environment

Swift 5.1.2
Xcode 11.2
MacOS 10.14.6

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Bug, AssociatedTypeInference, DiagnosticsQoI, ProtocolConformance, TypeChecker
Assignee None
Priority Medium

md5: 030b94e281d5eec3d58ed988895cfc10

Issue Description:

When conforming a type to Sequence or Collection, there is a “does not conform” error as expected, but no fixit to add stubs:

struct Foo: Collection {}
// Error: Type 'Foo' does not conform to protocol 'Collection'
// No fixit is offered
@beccadax
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beccadax commented Nov 7, 2019

@swift-ci create

@theblixguy
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It seems like associated type inference is preventing fix-its from being generated:

/Users/suyashsrijan/Documents/swift-src/swift/stdlib/public/core/Collection.swift:349:18: note: unable to infer associated type 'Index' for protocol 'Collection'
  associatedtype Index: Comparable
                 ^
/Users/suyashsrijan/Documents/swift-src/swift/stdlib/public/core/Range.swift:894:10: note: candidate can not infer 'Index' = '(UnboundedRange_) -> ()' because '(UnboundedRange_) -> ()' is not a nominal type and so can't conform to 'Comparable'
  public subscript(x: UnboundedRange) -> SubSequence {

If you specify the type for Index, then the fix-its are offered:

struct Foo: Collection {
  typealias Index = SomeType // <-- Add this
}

@NevinBR
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NevinBR commented Feb 5, 2020

If you specify the type for Index, then the fix-its are offered:

struct Foo: Collection {
  typealias Index = SomeType // <-- Add this
}

That is what I expect the fix-it to offer.

My memory of previous versions of Swift is that there used to be a fix-it to add exactly that.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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associated type inference bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself conformances Feature → protocol: protocol conformances diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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@beccadax @theblixguy @NevinBR