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[SR-4318] Useless diagnostic with type not conforming to Equatable #46901

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NachoSoto opened this issue Mar 22, 2017 · 9 comments
Closed

[SR-4318] Useless diagnostic with type not conforming to Equatable #46901

NachoSoto opened this issue Mar 22, 2017 · 9 comments
Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis

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@NachoSoto
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Previous ID SR-4318
Radar None
Original Reporter @NachoSoto
Type Bug
Status Resolved
Resolution Done

Attachment: Download

Environment

  • Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1)

  • Swift version 3.1 (swiftlang-802.0.48 clang-802.0.48)

  • Swift version 4.0 (swiftlang-900.0.59 clang-900.0.34.2)

  • Swift version 4.1 (swiftlang-902.0.34 clang-902.0.30)

Additional Detail from JIRA
Votes 1
Component/s Compiler
Labels Bug, DiagnosticsQoI, TypeChecker
Assignee None
Priority Medium

md5: 4231b4a94173b29ece8dca6219bf66e9

Issue Description:

protocol P {}
struct S: P {
    static func == (lhs: S, rhs: S) -> Bool { return true } 
}
func f<T: P>(_ a: T, _ b: (T, T) -> Bool) {}

func g<T: P>(_ a: T) {
    f(a, ==)
}

g(S())

Error:

error: repl.swift:8:10: error: ambiguous reference to member '=='
    f(a, ==)
         ^~

repl.swift:3:17: note: found this candidate
    static func == (lhs: S, rhs: S) -> Bool { return true }
                ^

In my project (with a not-reduced version of this) I actually get, quite literally, a lot of ambiguous references... (see screenshot)
@belkadan
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There's no direct connection between == and Equatable, which makes it hard to do better here in a completely generic way. But this may be a common enough case to be worth special-casing.

@belkadan
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I guess there is a connection if one of the candidates we find is in a protocol. Then we can suggest conforming to that protocol.

Swift.Equatable:149:24: note: found this candidate
    public static func ==(lhs: Self, rhs: Self) -> Bool
                       ^

But that wouldn't help for something like !=.

@jckarter
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jckarter commented Apr 4, 2017

There'd at least hopefully be fewer != overloads in the wild (and even fewer once conditional conformances work).

@jckarter
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jckarter commented Apr 4, 2017

The "connection if one of the candidates is in a protocol" sounds a lot like Doug's vague plan to optimize operator resolution by folding together candidates that look like a protocol conformance. I think the way we present this error is also pretty atrocious—I know it's all crammed in one note to work around Xcode's lack of good cross-file note support, but that's something that Xcode ought to fix. It'd still be somewhat more manageable to have one note per candidate.

@NachoSoto
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FYI Swift 3.1 produces the same result.

@NachoSoto
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I just filed SR-4795 with a similar problem.

@NachoSoto
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Still an issue in Swift 4.0

@NachoSoto
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Still an issue in Swift 4.1

@slavapestov
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#18831 (comment)

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
This issue was closed.
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Labels
bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. compiler The Swift compiler in itself diagnostics QoI Bug: Diagnostics Quality of Implementation type checker Area → compiler: Semantic analysis
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4 participants
@slavapestov @jckarter @NachoSoto @belkadan