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[SR-6803] Accept same-file extensions for automatic synthesis of Equatable/Hashable #49352

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NachoSoto opened this issue Jan 20, 2018 · 8 comments
Closed

[SR-6803] Accept same-file extensions for automatic synthesis of Equatable/Hashable #49352

NachoSoto opened this issue Jan 20, 2018 · 8 comments
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compiler The Swift compiler in itself improvement type checker Area → compiler: Semantic analysis

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@NachoSoto
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Previous ID SR-6803
Radar rdar://problem/39199726
Original Reporter @NachoSoto
Type Improvement
Status Resolved
Resolution Done
Environment

Swift version 4.1-dev (LLVM ef53654946, Clang f7df1e5a04, Swift 831b78c)

Additional Detail from JIRA
Votes 0
Component/s Compiler
Labels Improvement, TypeChecker
Assignee None
Priority Medium

md5: 7ee094bf8b76b4c699a3948b5de96775

relates to:

  • SR-4920 Compiler crash when extending type with Codable

Issue Description:

Conditional conformance doesn't work well with automatic synthesis of Equatable/Hashable because the only way to define conformance is in extensions, but automatic synthesis isn't allowed there.

Consider:

struct A<T> {
  let t: T
}

extension A: Equatable where T: Equatable {}

Expected result:

Code compiles, and Equatable is synthesized

Actual result:

error: repl.swift:5:1: error: type 'A<T>' does not conform to protocol 'Equatable'
extension A: Equatable where T: Equatable {}

See https://twitter.com/dgregor79/status/954524765003292672.
@belkadan
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@itaiferber, I know we had trouble doing this with Codable, but would your same work at least handle Equatable/Hashable? Maybe we can get that part in.

cc also @allevato

@itaiferber
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@belkadan The issue wasn't Codable-specific — we'd run into the same problems with Equatable/Hashable. The problem is that

struct Foo { ... }
extension Foo : Equatable {}

hits code paths in the compiler in a different order from

extension Foo : Equatable {}
struct Foo { ... }

IIRC, the second form compiles but the first does not. We should try to figure out a way around this if we can; let's continue via email. I'll be back in the office tomorrow.

@NachoSoto
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Are there plans to implement this for 4.1? I need to know whether I can count on these conditional conformances to be automatically synthesized.

@belkadan
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belkadan commented Feb 2, 2018

It's unlikely, sorry.

@NachoSoto
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So the 2 biggest features of Swift 4.1 won't actually work together 🙁

@huonw
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Mannequin

huonw mannequin commented Apr 5, 2018

@swift-ci create

@huonw
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Mannequin

huonw mannequin commented May 4, 2018

#16376

@huonw
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Mannequin

huonw mannequin commented May 7, 2018

90ba980

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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compiler The Swift compiler in itself improvement type checker Area → compiler: Semantic analysis
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3 participants
@itaiferber @NachoSoto @belkadan